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Effects of iodine deficiency on mental and psychomotor abilities.

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AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 53:55-67 (1980)
Effects of Iodine Deficiency on Mental and Psychomotor
Abi I ities
NICO BLEICHRODT,’ PETER J.D. DRENTH,’ AND ANDRIES QUERIDO*
Department of Industrial and Organizational Psychology and Test
Deuelopment, Free Uniuersity, Amsterdam, The Netherlands
KEY WORDS
Iodine deficiency, Goitre, Cretinism,
Mental and psychomotor abilities, Indonesia
ABSTRACT
Severe iodine deficiency may lead to endemic cretinism, which is
characterized by a number of abnormalities, such as mental retardation, neurological abnormalities and hearing disorders. These abnormalities may occur in various combinations, but impaired mental development is always a component.
The present study was attempted to determine whether there is also evidence of
mental retardation, perhaps to a lesser degree, in that part of the population that
manifest no symptoms of cretinism, the non-cretins, in an iodine-deficient area.
Results of an extensive test battery have been collected in two village populations: one village in an area with severe iodine deficiency and a control village in
a non-iodine-deficientarea, Both villages were situated in Central Java, Indonesia.
In the selected villages the total population between the ages of 6 and 20 years
participated in this study.
No evidence of significant mental retardation has been detected in the non-cretin
group in the severely iodine-deficient area. Significant differences between the
two populations, however, have been found with regard to a number of perceptual
and neuro-motor abilities.
Endemic goitre is very widely spread in
many parts of the world, particularly in developing countries. Kelly and Snedden (’60) estimate the total number of people suffering from
goitre at 200 million. It is generally assumed
that iodine deficiency is the major cause of endemic goitre. As a consequence of insufficient
iodine intake, the thyroid gland enlarges as a
sort of “compensation mechanism,” whereby
the surface is enlarged and the available iodine
is more efficiently taken up by the gland (Stanbury, ’54).A person is said to be suffering from
goitre when the lateral lobes of the thyroid
gland are larger than the distal phalanx of the
thumb of the person being examined. The size
of goitre can vary widely. Most investigators
have used the classification first proposed in
1960 by Perez et al., (WHO Monograph 44)and
slightly modified by the Scientific Group of the
Pan American Health Organization (Caracas,
1963, and Sao Paulo, 1973). The four categories
run from grade Ob (thyroid enlarged 2-4 x
normal size, detectable only by palpation and
not visible even when the neck is fully extended) through grade I to 111.The grade I11 is a
0092-948318015301-0055502.60 (c? 1980 ALAN R. LISS. INC.
very large goitre which can be recognized a t a
considerable distance. Goitre is considered to
be endemic when more than 5% of a n adolescent or pre-adolescent group have grade I
goitre, or when more than 3WG are classified in
any of the four grades just mentioned (Stanbury et al., ’74).
In severe iodine deficiency the prevalence of
goitre is accompanied by endemic cretinism.
Endemic cretinism is “the collective term for a
number of developmental abnormalities, which
geographically coincide with severe endemic
goitre and are caused by lesions acquired before
or shortly after birth. More precisely, it may be
defined as the excess of these abnormalities,
which is found in a goitrous population, as compared with a similar population without goitre,
and, in due time, is abolished by adequate
‘Senior Researcher and Professor at the Faculty of Psychology, Free
University of Amsterdam respectively; address. De Boelelaan 1081,
Amsterdam, The Netherlands.
2P~ofessor
of Medicine, University of Leiden; address: Rijnsburgerweg 10, Leiden, The Netherlands.
Received July 15, 1978; accepted January 28, 1980
55
56
N. BLEICHRODT, P.J.D. DRENTH, AND A. QUERIDO
goitre prophylaxis” (Choufoer e t al., ’65;
Querido, ’69).In some areas the percentage of
the population that is retarded as a result of
iodine deficiency can amount to more than 10%
(Querido et al., ’78).
Clinically, an endemic cretin can best be described as “a subject, born in an area of endemic
goitre, with irreversible damage to the central
nervous system, resulting in mental retardation andlor perceptive deafness and/or neuromotor disorders, which may be accompanied by
stunted growth and clinical hypothyroidism”
(Goslings et al., ’77). The neurological abnormalities and the bilateral hearing loss almost
certainly develop during the first 3-4 months of
the pre-natal period. Mental retardation ensuing from hypothyroidism can develop both during the pregnancy and in the first 3 years after
birth.
Mental retardation is the most significant
abnormality in endemic cretinism. The choice
of the instrument or procedure to determine the
mental level of people in an iodine-deficient
area is of great importance. Since cretinism
nowadays appears mainly in less developed
non-Western cultures for which no specific intelligence tests have been developed o r
adapted, and since, in addition, many cretins
are deaf and deaf-mute, which means an extra
handicap with regard to their testability, the
conclusion of Djokomoeljanto (’74) “that for
these population groups the assessment of
mental retardation is very difficult” seems justified. Various participants also raised this
problem at the International Symposium, held
in the Institute of Human Biology a t Goroka,
Territory of Papua and New Guinea in January
1971 (see Hetzel and Pharoah, ’72).
It will be clear that an exclusive utilization of
intelligence tests developed for Western cultures, such as the Leiter International Performance Scale (Lobo et al., ’631, the Stanford
Binet Intelligence Scale (Smith et al., ’57;
Fierro-Benitez et al., ’72, Trowbridge, ’72),the
Wechsler Scales (Smith et al., ’57) and the
Bender Gestalt Test (Greene, ’73), will, in general, lead to results that are less useful and are
difficult to interpret. It goes without saying
that the estimation of the level of mental development by purely impressive methods (Buttfield and Hetzel, ’69; Fierro-Benitez et al., ’69;
Delange et al., ’71;Ibbertson et al., ’71; Hornabrook, ’71; Pharoah, ’72) will be even less accurate.
In view of the inaccuracies of the testing and
measurement procedures the exact level of
mental retardation of cretins has been difficult
to diagnose. There seems to be little doubt,
however, as to the mental deficiency and subnormality of endemic cretins.
The question whether mental retardation
ensuing from iodine deficiency also occurs in
the non-cretinous sections of the population has
intrigued the medical and psychological scientist in this area of research for quite some time.
A number of studies have led to the supposition
that mental abnormalities do indeed occur in
the “healthy” section of the population in an
iodine-deficient area. Four studies (Dodge et
al., ’69; Fierro-Benitez et al., ’72; Trowbridge,
’72; Greene, ’73) have been carried out in an
iodine-deficient area in Latin America (the
highlands of Ecuador). All four studies seem to
confirm the hypothesis that iodine deficiency
does have a negative influence on the cerebral
functions. In the first three studies this conclusion is based on the finding t h a t iodine
prophylaxis seemed to have a positive effect on
the general mental development. The latter
study, using the Bender Gestalt Test, has indicated that a large proportion of the non-cretin
group showed strong indications of a neurological deficit in visual motor perception. Again, in
view of the “Western” intelligence tests being
used, and since no specific adaptation of these
tests for the population under study has been
made, serious reservations with respect t o
these conclusions seem justified. A replication
of these studies with more suitable instruments
was thought t o be necessary in order to find an
answer to the scientifically interesting and
practically highly relevant question of the influence of iodine deficiency on mental developments in a non-cretinous population.
A PRECEDING STUDY
In 1973 and 1974 an attempt was made to
incorporate this research plan in a larger study
carried out by a joint group of medical researchers from the Leiden University, Holland,
and the Diponegoro University, Semarang, Indonesia. The study, which had been carried out
in Central Java, Indonesia, tried to investigate
whether mental retardation, hearing loss and
hypothyroidism were present in the non-cretinous part of an affected population in a severely iodine-deficient area with high goitre
rate and endemic cretinism.
In order to answer this question, the population of a village Ngampel in Central Java (as
representative for the severely iodine-deficient
area) has been investigated with respect to a
number of parameters for iodine metabolism
and for mental and somatic development. In
IODINE DEFICIENCY AND MENTAL DEVELOPMENT
addition these data have been compared with
similar data obtained in a control village, Lonjong, with a population that did not suffer from
goitre. This village had been chosen for its similarity to Ngampel in social economic development and environmental and educational conditions. In both areas a 50% random population
sample aged 5 2 0 years was studied.
For the present study the findings with respect to the scores on the intelligence test
(Raven Coloured Progressive Matrices) for the
two village populations were most interesting.
The results are presented in Table 1.From the
evaluation of these results, Djokomoeljanto
concludes in his thesis (’74) that “the data
strongly suggest that the non-cretinous part of
the population in the severely iodine-deficient
area is slower in development and specifically
is affected in mental development.”
Two remarks should be made with respect to
this conclusion. First, it is striking that the
significant difference which is found in the
total group seems to occur only in the youngest
and the oldest age groups. In the middle age
groups (7 through 16) the differences are not
significant and often are even negligible. In
other words, if there is a difference in test performance, it is not a phenomenon equally
applicable for each of the various age groups.
Second, it should be pointed out that the test
used (Raven Coloured Progressive Matrices)
has never demonstrated a culture-free character (Drenth, ’751, nor has it been adapted specifically for this rural and remote population in
Central Java.
It was clear that a more appropriate approach to answer the questions with regard to
mental development was necessary. A replication with better adapted and more applicable
intelligence tests, and also with a larger variety of mental and psychomotor abilities was
considered desirable and has been planned subsequently. In the next sections the purpose, design and results of this ensuing study will be
presented and discussed.
57
teristics besides intellectual cognitive abilities,
was planned. More specifically the following
questions have been formulated:
1)Are there differences in the general level
of intelligence between the “non-cretins” in a
severely iodine-deficient area and the population in an (otherwise identical) non-iodine-deficient area?
2) Are there any qualitative differences in
mental ability, i.e. differences in the structural
composition of the intelligence, between the
two populations?
3) Are there any differences in non-intelligence characteristics (motor skills, concentration, perceptual capacities) between the two
populations?
4)Do the differences between the two populations increase with age?
SELECTION OF INSTRUMENTS
In the first phase of the study an experimental test battery has been administered to a
random sample aged between 5 and 20 years
taken from the population of Ngampel, the iodine-deficient village that has been used in
the previous study reported by Djokomoeljanto.
A total number of 95 children were tested: 26
children in the age group 5 8 , 36 in the age
group 9-12, and 33 in the age group 13-20. In
Table 2 the educational levels for the three age
groups and the total group are described. In the
two lowest age groups there were no significant
differences in educational level between boys
and girls. In the highest age group the girls
showed a somewhat lower average in the
number of years schooling. Staff members and
students from the Psychology Faculty, Universitas Indonesia, Jakarta, acted as test leaders
after a training in the administration and scoring of the tests.’
Most of the intelligence tests were taken
from the Test Intelligensi Anak (Drenth et al.,
’75), and from the Test Intelligensi Kolektip
Indonesia (Drenth, et al., ’76,’77,’78)developed
in cooperation between Free University of
Amsterdam and the Padjadjaran University of
OBJECTIVES
Bandung, Indonesia. Other tests have been
The general objective of the study carried out selected from the French Kit of reference tests
in 1975 and 1976 was to replicate the study for cognitive factors (French et al., ’63), and
indicated above as to the possible negative in- included the Raven test series (’62). Others
fluence of iodine deficiency on general mental were specifically developed a t the Department
development within a non-cretinous popula- of Industrial and Organizational Psychology
tion. It was hoped to be possible to employ bet- and Test Development at the Free University
ter and specifically adapted intelligence tests in Amsterdam.
than those used in the previous studies.
‘Participating in the project “Iodine-Deficiency and Physical and
Moreover, an extension of the investigation, Mental
Development” (IDD) were Drs. E. Bonang, Dr. S. Sadli and Dr.
including the study of several other charac- S. Wibowo.
N. BLEICHRODT, P.J.D. DRENTH, AND A. QUERIDO
58
TABLE 1 . Means and standard deuiations on the Raven Coloured Progressive Matrices
for different age groups from Lonjong and Ngampel (non-cretins)
Lonjong
Ngampel
Age
group
(years)
N
Mean
S.D.
N
Mean
S.D.
5-6
7-8
$10
11-12
13-14
15-16
17-20
9
7
16
9
11
13
7
18.1
20.6
22.2
23.0
23.9
22.8
28.0
3.1
3.7
3.8
6.1
3.6
3.9
4.4
15
10
17
13
11
7
18
13.4
17.7
19.6
23.5
23.0
21.1
20.3
3.6
4.2
4.2
5.4
3.7
4.5
6.0
*
520
72
22.6
4.6
91
19.6
5.5
*
Significance of
difference
*
*Significant at 1%level
TABLE 2. Educational level (number of completed school years) for the three age
Eroups and the total group in Npampel
Secondary
education
Primary education
Age group
(years)
N
0
1
2
3
4
5
6
1
3
4
5-8
$12
13-20
26
36
33
17
5
7
10
2
5
5
7
5
4
7
5
9
2
2
1
2
5-20
95
12
12
11
14
2
2
1
2
22
17
The instructions have been translated or
formulated in Javanese, the language spoken
in Central Java.
The objective of the pilot testing was to inves-
tigate the usefulness of the tests, the appropriateness of the instructions, optimal time limits,
the reliability of the tests, interrelations of the
tests, optimal sequence of the tests, etc.
The following tests for the three age groups have been selected for the definite study:
6 to 8 years
1 Fluency
2 Visual memory A
3 Learning names
4 Exclusion A
5 Quantity
6 Discs
7 Verbal meaning
8 Formboard
9 Pinboard
10 Throwing balls A
11 Balance
12 Simple reaction time
13 Choice reaction time
14 Tapping test
9 to 12 years
1 Fluency
2 Visual memory B
3 Learning names
4 Exclusion B
5 Discs
6 Verbal meaning
7 Formboard
8 Pinboard
9 Progressive matrices
10 Memory span
11 Figure comparison
12 Hidden patterns
13 Block design
14 Throwing balls B
15 Balance
16 Simple reaction time
17 Choice reaction time
18 Tapping test
13 to 20 years
1 Fluency
2 Visual memory B
3 Exclusion B
4 Discs
5 Progressive matrices
6 Memory span
7 Figure comparison
8 Hidden patterns
9 Block design
10 Mazes
11 Figure exclusion
12 Components
13 Throwing balls C
14 Balance
15 Simple reaction time
16 Choice reaction time
17 Tapping test
IOIIINE DEFICIENCY AND MENTAL DEVELOPMENT
59
The composition of the definite test batteries
for the three age groups was based on the following considerations:
certain order, in matching holes on the formboard. The score is the total time required t o
place all the figures in the holes.
1)The test had to be sufficiently reliable (if
necessary after improvement by rejecting
items with a too low item-test correlation or a
too high or too low difficulty level).
2) Tests that had sufficient applicability in
more than one age group were preferred to tests
that were more age-specific.
3) The pattern of interrelationships between
the tests had to show a sufficiently varied and
balanced selection of instruments.
In the following paragraphs we present a
short description of the various subtests.
Memory span. Subject has to memorize the
sequence of a number of figures varying from 3
to 7, and rearrange a number of blocks on which
similar figures are depicted according to this
sequence.
Fluency. Subject has to give as many Christian names of boys and girls as possible, and as
many names of animals as possible within a
two-minute period.
Visual memory. The subject is shown an
abstract figure for five seconds and subsequently has to recognize the figure among
four, five or eight more or less similar figures.
Learning names. Subject has to learn names
of ten animals. The series of animals is shown
three more times, whereby the subject has to
give the appropriate names. At each incorrect
response, the correct name is given by the test
leader. The score is the total number of correct
responses during the three trials.
Exclusion. Subject is required to indicate
which of four objects or abstract figures does not
belong.
Quantity. Subject has to estimate the differences in number, length, and quantity of pictorial objects. The tasks vary from “choose the
longest skipping rope” to “in which glass is the
most lemonade” and “which row has the most
red balls.”
Discs. The task here is to place two layers of
discs with holes over a set ofmatchingpins. The
test leader places the first layer. The score is
the total time required to place all 18 discs.
Verbal meaning. Subject has to select from
four different pictures, (objects, animals, situations) the picture that corresponds to a
stimulus word.
Formboard. Subject has to place two sets of
ten geometric figures that are presented in a
Coloured progressive matrices. Subject is directed to select one of six figures to complete
incomplete patterns.
Hidden patterns. Subject has to recognize a
simple design (the “labda” sign) that is embedded in slightly more complex drawings. Of 20
rows of ten drawings only those containing that
design should be marked.
Block design. The subject has to arrange flat
square blocks, the surfaces of which are either
white, red or half whitehalf red according to
given patterns. The number of blocks are either
4 or 6. Scoring is based on the time used for
completion.
Mazes. Subject has to trace quickest way to
exit in 20 mazes differing in degree of difficulty.
Scoring is based on the time used for completion.
Figure exclusion. The subject is shown five
figures, four of which have one feature in common, and has to indicate the figure that does
not belong.
Components. Subject has to indicate which
two of six complex figures can be constructed by
uniting two given small figures (the components).
Figure comparison. Subject has to select from
a row of six rather similar figures, two of which
are identical to a key figure given a t the left of
the row.
Pinboard. Subject is instructed to take pins
from a box and insert them into the holes on a
board as quickly as possible.
Throwing balls. Twenty small balls have to
be thrown into a basket 26 cm in diameter. The
throwing distance varies with age group (6-8
years: 3 metres, 9-12 years: 4 metres, and
1Zb-20years: 5 metres).
60
N. BLEICHRODT, P.J.D. DRENTH, AND A. QUERIDO
Balancing. The subject has to stand on one
leg as long as he can. The test is ended when his
other foot touches the ground. The exercise is
repeated for the other leg. The score is the mean
time the subject remains standing on one leg
(time limit 3 minutes).
Simple reaction time. Subject has t o press a
button as soon as a red light is switched on. The
stimuli are presented with varying interstimulus intervals. There are four series of
19 stimuli. The score is the mean reaction time
over the four series.
Choice reaction time. Subject is given one of
two possible visual stimuli, after which he has
to press the corresponding button as quickly as
he can. A total of four series of 19 stimuli are
presented. The score is the mean reaction time
for the four series.
Tapping. Subject is required to tap two
hatched rectangular plates with a pencil as rapidly as possible. The plates have to be struck
successively. Movement tolerance and amplitude are controlled by fixing the width of
the plates and the distance between them.
There are ten items with varying target size
and distances between the target plates. The
task is accomplished primarily by movements
of the lower arm. The score is the mean number
of hits over the ten items.
DEFINITE STUDY
Description of the test villages
For the definite study two village populations have been compared: one village in an
area with severe iodine deficiency and a control
village in a non-iodine-deficient area. The
selected villages are both situated in Central
Java. The iodine-deficientvillage Gowok is situated on the Western slope of the Merapi, 30
km east of Magelang ( 2 110,000 inhabitants).
Gowok belongs to the same kelurahan Sengi (?
3,150 inhabitants) as the previously somatically intensively studied adjacent village
Ngampel (see Selection of Instruments). The
control village, Lonjong, belonging to the
kelurahan Lonjong (* 3,050 inhabitants), is
situated t 25 km northeast of Magelang, about
equidistant from Bawen and Ambarawa.
An important condition in the study is, of
course, the comparability of the two villages
with the exception of iodine excretion, goitre
rate and the presence or absence of endemic
cretinism. With regard to the difference of
iodine supply it should be mentioned that in
*
Lonjong the goitre rate (Ob) was 3% and cretinism was absent. Furthermore, in the previous study the indices for thyroid function in the
control village were all normal: the average
PBI was 4.9 pg per loo%, and the serum
thyrotropic hormone levels were all normal.
Achilles tendon reflex time fell within normal
limits for Western countries (Goslings et al.,
'77). No change in urinary iodine excretion had
occurred in Lonjong since the previous investigations. In Gowok the parameters studied were
proof of severe iodine deficiency. Aside from a
high goitre rate and the presence of 4.5% cretinism, the average serum PBI-level in the
6 2 0 years sample was only 3.4 pg per 100 ml
serum. The average serum thyrotropic hormone levels were elevated to 18.4 pUiml.
These parameters, together with the low urinary iodine excretion in Gowok, warranted the
conclusion that with regard to iodine metabolism Gowok was a severely iodine-deficient village. A great effort was made to select
two villages that were equivalent with respect
to a number of geographical and socio-economical and developmental characteristics, although it should be acknowledged that absolute comparability can never be achieved. In
Table 3 the two villages Lonjong and Gowok are
compared with respect to a number of relevant
characteristics.
Attention had also been given to the presence
or absence in Lonjong and Gowok of other nutritional deficiency, such a s protein-caloric
malnutrition. In neither of the villages was
marasmus or kwashiorkor seen. In the previous
study the urinary nitrogen excretion per gram
2.4 and 5.3 & 2.0 for
creatinine was 6.5
Ngampel and Lonjong, respectively. In Gowok
(a village very similar to Ngampel, as previously stated) the urinary nitrogen excretion
was 5.3 _t 2.7 per gram of creatinine (N = 35)in
the G20 year group, and therefore in the same
range as Lonjong and Ngampel. Height could
not be used as an index because of the presence
of hypothyroidism, as was shown by Goslings et
al. ('77). The total serum protein levels in
Gowok were 7.7 ? 0.06 (N = 39) per 100 ml
serum, and therefore normal.
It has been shown that the two villages do
indeed differ regarding the experimental variable iodine deficiency and its consequences.
Unfortunately, however, the villages also differ
in two other important factors, namely the degree of isolation and the level of education,
which will be discussed later. Especially, the
last difference will have to be taken into account if the results on possible differences in
intelligence are to be interpreted.
*
61
IODINE DEFICIENCY AND MENTAL DEVELOPMENT
TABLE 3. Several characteristics of the dukuh
Lonjong (kelurahan Lonjong) and the dukuh
Gowok (kelurahan Sengi)
Variables
Lonjong
Gowok
Number of inhabitants
Farmers
Distance from Magelang
Distance from paved
road
Altitude
Number of schools
Distance from primary
school
489
99%
23 km
lkm
41 1
100%
30 km
5 km
-t 600m
none
1 km
600m
none
4 km
Goitre rate (0b
included)
Goitre rate (0 b
excluded)
Endemic cretinism
Iodine excretion pgig
creatinine
3%
k
68%
0%
-C
46%
absent
41
4%%
18
~
*
Description of the test group
In the two villages, the total population between the ages of 6 and 20 years have been
included in the study with an exception of two
groups: In the first place no data have been
collected for the group of cretins for the iodinedeficient village. Second, subjects who had received more than primary school education
have also been excluded, this occurring in Lonjong (six persons). The exclusion of the more
educated people was done because they stood a
better chance of higher test scores, particularly
on tests that measure aspects of intelligence
that are closely related to school achievement.
In Table 4 a description is presented of the
two populations in Lonjong and Gowok. We see
that as far as age is concerned the two villages
are quite comparable. In terms of number of
years of education, however, we see clear differences between the two populations as has
been indicated above. This difference in education is not very strong in the youngest age
group, but is particularly strong in the two
older age groups. Since the conclusions with
respect to differences in intelligence will be
confounded by the educational factor, it has
been decided to include the data from the tryout sample (the iodine-deficient village,
Ngampel) in this definite study, since the level
of education in Ngampel is virtually identical
to that in Lonjong (see Table 2). Of course the
data have been treated separately, and are only
used to support possible conclusions on the
basis of a comparative analysis on the two populations of Lonjong and Gowok. Two considerations have to be mentioned with respect to the
following:
First, it should be kept in mind that the pilot
sample has been used primarily in order to test
the tests. Accordingly, the tests used in Ngampel are not identical with the ones used in the
definite study. In a number of tests certain
items have been removed, due to lack of item
discrimination or insufficient variance. Of
course, the test data from the Ngampel group
have been adapted in the sense that the testee’s
scores are based on items that are selected for
the definitive test series. Moreover, for a
number of subtests (throwing balls, balance,
reaction time, tapping test) no data have been
collected in Ngampel a t all.
Second, two years before the test administration the entire population of Ngampel had been
injected with iodized oil. This had obvious consequences for the physical development of the
population in the area concerned, since hypothyroidism, if present, has been corrected. It is
unlikely, however, that this iodine administration had any corrective influence on mental
abnormalities, since it is known that this can
only be expected when intervention occurs during the first years of life. In the light of these
observations, the data from Ngampel have
been included in the further analysis of the
results and were used as possible support for
outcomes based on data from Lonjong and
Gowok.
Reliabilities of the tests
Reliabilities, in the sense of internal consistencies, have been calculated for the tests on
TABLE 4. Number of testees, age and educational level (number of completed school
years) for the three age groups and the total group
Lonjong
Age
(years)
N
age
Gowok
education
N
age
education
0.1
0.3
0.6
0.4
$12
13-20
40
41
58
7.2
10.5
15.6
0.4
2.6
4.1
21
41
44
7.1
10.6
16.1
e20
139
11.7
2.5
106
12.2
6 8
62
N. BLEICHRODT, P.J.D. DRENTH, AND A. QUERIDO
the definitive test group, by means of the splithalf method. For most tests, the items could be
divided into even-numbered and odd-numbered
halves. This method was applied for the following subtests: visual memory, exclusion, quantity, verbal meaning, tapping test, progressive
matrices, figure comparison, block design,
mazes, figure exclusion, components. A
number of other tests were split into a first and
second half: fluency, discs, formboard, balance,
memory span. For the reaction time tests correlations have been calculated for the mean
scores on the second and third series. In Table 5
the internal consistency coefficients corrected
for test-halving by means of the SpearmanBrown formula are presented. No reliabilities
could be calculated for the subtests learning
names, pinboard, throwing balls, and hidden
patterns. It can be seen that the reliability coefficients for almost all subtests are very reasonable, being above .70 and in more than half of
the cases above .80. For the two tests with
slightly lower reliability coefficients (fluency
and formboard), a lower split-half consistency
could be expected in view of the difference in
content of the tasks in the two halves.
RESULTS
Three preliminary remarks have to be made
before the results are presented and discussed.
First, a separate analysis has been made for
each of the three age groups: 6-8-year-olds,
9--12-year-olds, and 13-20-year-olds. As has
been shown in Table 4,the differences in educational level become more pertinent in the two
older age groups.
Second, no data are given for the group of
boys and the group of girls separately, since no
clear differences in test achievements between
the two groups were found. This also meant
that it was unnecessary to control for sex.
Third, the tests can be divided into three
categories: first, the intelligence tests that are
more susceptible to educational influences as
has been shown in previous work with these
and similar tests (Drenth et al., '75, Schmidt et
al., '75, Drenth, '77). These are visual memory,
learning names, exclusion, quantity, verbal
meaning, memory span, progressive matrices,
figure comparison, hidden patterns, block design,mazes, figure exclusion, components. Second, tests that are less susceptible to educational influences: fluency, discs, formboard.
And finally, tests that measure more perceptual and psychomotoric aspects and which are
less connected with educational achievement
also: pinboard, throwing balls, balance, simple
reaction time, choice reaction time, tapping
test.
Results for the 68-year-olds
Table 6 presents the results for the age group
6-8 from Lonjong, Gowok and Ngampel. As has
been stated earlier, the groups in this age
range are rather comparable in terms of education, but in order t o increase the comparability
the data for two groups of children (Lonjongand
Gowok) who have received less than one year of
education have been added in parentheses.
The following conclusions can be drawn from
the data presented in Table 6:
TABLE 5. Coefficients of internal consistency calculated for the three age groups: 6-8
(N = 61),9-12 (N = 821, 13-20 (N= 102)
Tests
Fluency
Visual memory
Exclusion
Quantity
Discs
Verbal meaning
Formboard
Balance
Simple reaction time'
Choice reaction time'
Tapping test
Progressive matrices
Memory span
Figure comparison
Block design
6-8 yr
%12 yr
13-20 yr
.52
.85
.66
.83
.a0
.77
.84
.79
.73
.74
.62
.71
.92
.92
.93
.77
.a0
.84
.73
.79
.53
.63
.87
.93
.94
.95
Mazes
Figure exclusion
Components
'The coefficients of internal consistency for the three age-groups were calculated on 29, 49 and 56 subjects respectively.
.a1
.91
.a9
.95
.84
.74
.95
.90
.79
.73
.a9
IODINE DEFICIENCY AND MENTAL DEVELOPMENT
(1)There is no difference in intelligence between the two groups, either with respect to the
tests that are educationally loaded, or with respect to the intelligence tests that are less susceptible to educational influences. This conclusion is also supported by the data collected in
Ngampel.
(2) With respect to the psychomotoric tests,
the performance on the reaction time tests and
gross motor activities in Gowok are somewhat
poorer than in Lonjong, but the differences are
not significant. With respect to the motoric activities that require speed and precision (pinboard and tapping test) the differences reach a
1%level of significance, a finding supported by
the results on the pinboard in Ngampel.
Results for the 9-12-year-olds
As has been said, the level of education of the
group of children tested in Lonjong differs considerably from that in Gowok. For this reason
the data from the try-out village, Ngampel,
with an educational level rather comparable
with that of Lonjong have been included. Table
7 presents the means and standard deviations
per subtest for the three villages.
The following conclusions can be drawn from
the data presented in Table 7:
(1)For the intelligence tests that are less
susceptible to educational influences no significant differences have been found for the villages Lonjong and Gowok. This finding is supported by the data from the village Ngampel.
(2) For the intelligence tests that are more
strongly susceptible to educational influences,
significant differences have been found in the
two villages. The explanation, however, that
these differences are caused primarily by educational differences and not by differences in
iodine intake is supported by the data from the
village Ngampel; scores on all these tests are
not significantly lower from those in Lonjong.
(3)An exception has to be made for the figure
comparison test, which showed poorer results
both in Gowok and Ngampel. In factor analytic
studies, however, this test usually does not load
on one of the central intelligence factors but
calls for speed and accuracy in visual perception (Drenth et al., ’77).
(4)With respect to the psychomotoric and reaction time tests, the results seem clear. All the
differences with respect to these tests reach a
1%level of significance. As far as the pinboard
is concerned, this result is supported again by
the data from Ngampel, where we also find a
significantly poorer performance.
63
Results for the 13-20-year-olds
In this age group, again a very strong difference is noticeable in the level of education between the two villages. It was not possible to
find a reasonable number of people in the two
villages who were comparable with regard to
their level of education. As a consequence,here
again, the data from the village Ngampel, in
which the level of education for this age group
is comparable to that in Lonjong, have been
included to support possible findings or explanations. The results for this age group are
presented in Table 8.
In Table 8,the findings are more or less similar to those in Table 7. Differences in intelligence tests seem to be explainable to quite some
extent in terms of differences in average educational level in the two villages, Lonjong and
Gowok, since no support for the conclusion that
iodine deficiency might be responsible for these
differences is given by the data from Ngampel.
(An exception has to be made for the fluency
test, which produces significant differences
both in Gowok and Ngampel.)
A consistent significant difference is found
for the figure comparison and components
tests. This result is similar to that in the previous age group. Figure comparison measures
perceptual speed, and this same perceptual factor is probably responsible for the performance
in the test components.
The reaction time tests and the tapping test
show the same consistent differences as in the
two previous age groups. The difference in balance has not reached the l%level of significance, and for throwing balls no difference has
been found a t all.
SUMMARY AND OVERALL CONCLUSION
In Table 9 a general summary of the outcomes of the comparative study for the three
age groups is presented. For the two villages,
Gowok and Ngampel, a n asterisk indicates a
difference with the control village Lonjong at
the 1%level of significance. Under the section
titled “objectives of the study,” four questions
have been formulated. An attempt will be made
to answer these questions in the following discussion.
Question 1
Are there any differences in the general level
of intelligence between the %on-cretins” in a
severely iodine-deficient area and the population in an (otherwise identical) non-iodine-deficient area? Upon initial viewing, the number
64
N. BLEICHRODT, P.J.D. DRENTH, AND A. QUERIDO
TABLE 6. Means and standard deviations for children in the age group 6.4 from
Lonjong 1N = 40), Gowok (N = 211 and Ngampel IN = 211
Lonjong
Gowok
Tests
Mean
S.D.
Fluency
22.5
(20.4)
18.9
(16.6)
9.2
( 8.0)
19.1
(17.6)
16.9
(16.2)
455.4
(489.2)
13.7
(13.3)
405.0
(454.8)
362.8
(387.7)
16.2
(15.3)
121.9
(103.5)
528.6
(585.4)
948.9
(1058.0)
29.6
(28.3)
7.4
(6.4)
6.7
(5.9)
4.2
(4.2)
5.3
(5.0)
4.6
(3.6)
140.7
(149.7)
3.8
(3.2)
140.8
(122.9)
67.4
(64.6)
2.8
(4.1)
63.3
(68.6)
158.2
(62.5)
214.0
(202.0)
5.1
(4.5)
Visual memory A
Learning names
Exclusion A
Quantity
Discs'
Verbal meaning
Formboard'
Pinboard'
Throwing balls A
Balance
Simple RT'
Choice RT'
Tapping test
Mean
Ngampel
S.D.
23.3
(23.9)
17.5
(17.3)
8.0
( 7.8)
18.3
(17.8)
18.2
(18.2)
453.4
(461.7)
12.4
(12.0)
405.1
(426.5)
447.8**
(451.6)**
15.2
(15.3)
91.9
(87.5)
540.8
(548.7)
976.1
(985.8)
25.6**
(25.0)
9.5
(9.4)
5.6
(5.6)
3.1
(3.0)
7.7
(7.5)
4.0
(4.1)
253.1
(256.8)
3.5
(3.2)
161.1
(155.2)
108.1
(109.5)
5.2
(5.4)
76.9
(75.9)
119.3
(120.2)
197.8
(191.0)
7.7
(7.3)
Mean
S.D.
19.1
9.1
19.8
10.9
9.0
4.6
20.6
6.8
16.7
4.7
447.0
149.2
15.1
3.7
432.8
151.2
447.1**
131.5
**p < .01, *p < .05(one-tailed), as compared with Lonjong.
'Scoring is based on the time of completion, lower scores are better (in t h e remaining tests, the higher scores are better)
TABLE 7. Means and standard deviations for the 9-12-year age groups from h n j o n g
(N = 411, Gowok (N = 41) and Ngampel ( N = 36)
Lonjong
Tests
Fluency
Visual memory B
Learning names
Exclusion B
Discs'
Verbal meaning
Formboard'
Pinboard'
Progressive matrict?S
Memory span
Figure comparison
Hidden patterns
Block design'
Throwing balls B
Balance
Simple RT'
Choice RT'
Tapping test
Gowok
Ngampel
Mean
S.D.
Mean
S.D.
Mean
S.D.
28.7
16.4
14.0
20.8
305.0
16.1
263.1
294.4
18.8
13.9
21.5
117.9
521.1
14.4
146.9
444.5
783.7
35.6
8.1
3.9
5.1
5.5
124.6
2.5
78.4
68.4
5.9
4.6
6.4
11.6
113.4
2.6
48.6
82.8
120.4
6.2
25.5
10.9*
11.v
15.2**
320.4
13.1**
320.0
382.2**
14.1**
6.P*
11.2**
114.3
626.1**
12.4**
115.7**
513.7**
917.1
31.4**
10.5
5.5
5.8
5.4
190.9
3.3
149.0
83.0
5.2
4.4
5.4
9.8
137.9
3.8
63.8
109.3
211.1
6.7
27.3
17.9
15.6
21.3
330.6
16.1
327.9
348.6**
20.2
11.8
16.W*
113.3
505.7
7.7
6.2
6.1
6.3
136.6
5.2
181.6
101.6
5.3
5.0
8.6
8.0
118.0
**p < .01,* p < .05 (one-tailed), as compared with Lonjong.
'Scoring is based on th e time of completion, lower scores a r e better (in the remaining tests, the higher scores are better)
65
IODINE DEFICIENCY AND MENTAL DEVELOPMENT
TABLE 8. Means and standard deviations for the age group 13-20 from Lonjong
( N = 581, Gowok (N = 44)and Ngampel (N = 33)
Gowok
Lonjong
Tests
Mean
~~
~~
Fluency
Visual memory B
Exclusion B
Discs'
Progressive matrices
Memory span
Figure comparison
Hidden patterns
Block design'
Mazes'
Figure exclusion
Components
Throwing balls C
Balance
Simple RT'
Choice RT1
Tapping test
~~
Ngampel
S.D.
Mean
S.D.
Mean
S.D.
10.1
4.4
5.1
83.0
6.5
4.3
5.9
14.1
121.6
155.7
3.9
6.1
2.6
41.1
64.1
90.4
6.9
30.3**
13.4**
16.8**
292.5
17.5**
9.F*
16.4**
112.3**
495.3**
537.3
9.9*
9.6
5.1
4.9
191.8
4.5
4.0
7.3
11.7
143.0
194.2
3.9
5.0
3.3
50.0
108.3
104.2
6.3
30.7**
19.7
22.9
226.6
24.0
13.3
17.7**
121.5
400.2
562.8
10.3
10.7*
8.7
5.1
5.1
103.0
4.9
4.7
8.5
15.2
111.5
192.2
4.9
5.3
~
39.4
18.3
21.9
231.0
22.4
14.0
25.6
123.9
373.5
495.4
11.9
14.6
12.5
155.3
360.8
630.3
45.7
8.W*
12.8
141.4
438.5**
716.F*
38.4**
**p 4 .01, * p < .05 (one-tailed), as compared with Lonjong.
'Scoring is based on the time of completion, lower scores are better (in the remaining tests, the higher scores are better).
TABLE 9. Summary of the differences in test achievements between Lonjong and Gowok
with, in parentheses, the differences between Lonjong and Ngampel
Tests
Visual memory (A,B,B)
Learning names
Exclusion (A,B,B)
Quantity
Verbal meaning
Progressive matrices
Memory span
Hidden patterns
Block design
Mazes
Figure exclusion
Components
Figure comparison
Gowok
Ngampel
-
(-1
(-1
(-1
Gowok
**
*
**
**
**
**
-
**
**
Ngampel
(-1
(-1
(-1
Gowok
**
(**I
-
-
**
** Significant at 1%level; * significant at 5% level; -not
significant
**
**
**
**
**
**
Ngampel
**
(-1
**
(-1
**
**
**
**
**
**
**
(-1
(-1
(-1
Fluency
Discs
Formboard
Pinboard
Throwing balls (A,B,C)
Balance
Simple reaction time
Choice reaction time
Tapping test
13-20 year
%12 year
6-8 year
-
-
**
**
**
66
N. BLEICHRODT, P.J.D. DRENTH, AND A. QUERIDO
of significant differences found in the village
Gowok seem to indicate that this question has
to be answered affirmatively. Further critical
analysis, however, has brought the authors to
the conclusion that a negative answer on this
question is justified.
First, the differences between Gowok and
Lonjong are almost never supported by the data
from the village Ngampel, which is located in
an iodine-deficient area, but which has a level
of education comparable to Lonjong. Second,
hardly any difference exists for the lower age
group, which is the most comparable of the
three sets of age groups with respect to educational level. Third, differences are absent or
much smaller with regard to tests that are less
susceptible to educational influence. In other
words, the differences that have been found can
be explained in terms of differences in educational level and disappear if a research design would control for this contaminating factor.
Question 2
Are there any qualitative structural differences with respect to intelligence between the
two tested populations?
On the basis of the results of this study, this
question may be answered negatively as well.
With regard to more specific aspects of intelligence, no clear differenceshave been found that
could be attributed to the presence or absence of
iodine.
Question 3
Are there any differences in non-intelligence
characteristics between the two tested populations?
Based on the empirical results the answer to
this question can be affirmative. In the first
place, characteristics in the psychomotoric domain show clear differences. Four tests (pinboard, simple reaction time, choice reaction
time, tapping test) show significant differences
in a t least two of the three age groups, whereas
two other motoric tests (throwing balls and
balance) in one age group show significant differences, while the differences in one other
group are in the same direction. It seems likely
that the iodine deficiency did affect the development of the so-called perceptual motor
abilities which have been described by
Fleishman ('72).The followingfour specific factors from Fleishman's model seem to be relevant:
a) Finger dexterity: skill in handling smaller
objects, involving primarily the fingers (pinboard).
b) Manual dexterity: coordination and control of arm/hand movements necessary for the
manipulation of objects (tapping test and pinboard).
c)Reaction time: the speed with which an
individual is able to react to a given stimulus.
d) Response orientation: speed in choosing
the correct response when several stimuli are
offered (choice reaction time).
Also, differences were observed between
Lonjong on the one hand and Gowok and
Ngampel on the other, for the subtest figure
comparison, which is indicative of the perceptual speed factor (French et al., '63). Some support for this finding can be found in the fact that
the components test, which partly calls for the
same factor, also shows significant differences.
Question 4
Do the differences between the two populations increase with age?
It will be clear that since no significant differences could be found with respect to intellectual capacities, equally little evidence has been
providedfor an increase in differences with age.
The differences in test performance in the village Gowok is, as has been explained above,
likely due to the differences in educational
level. Inspection of Table 9 with respect to the
tests that do show differences between non-iodine-deficient and iodine-deficient villages
seems to indicate that the differences become
larger in the older age groups. However, the
differences for the 6-8 age group were also in
the same direction, but did not reach the 1%
level of significance, possibly due to the smaller
size of the sample. Anyway, it does not seem
justified to conclude that an increase in differences in test performance is connected with
age.
The overall conclusion from this study therefore would appear to be that there is no continuum in mental deficiency as caused by iodine
deficiency with the strong subnormality within
the cretin group as the one extreme pole. The
present study has provided empirical evidence,
however, for the theory that iodine deficiency
causes gradual degeneration with regard to
other abnormalities of the central nervous system, i.e. perceptual speed and accuracy and
particularly neuromotor abilities.
IODINE DEFICIENCY AND MENTAL DEVELOPMENT
But ultimately, further research will be required to answer the questions of why this differential effect of severe iodine deficiency occurs within the non-cretin population, a t what
stage of the development in the prenatal phase
or in the post-natal years the inadequate
thyroid hormone supply leads to these effects,
and, more specifically, a t what stage of development the deficiency can be cured or prevented.
67
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