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A ttwol® submitted in j*rti*l fulfillment of I'm requirements
for th« degree of gtoetor of F&iloaopii^, in the Oep&rtsaont
of Child Half are in the Oradoat,® College of tb*
State Cnlwreiiy of low*.
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' ACKSfOWlEdOMMIS
The writer wishes to express appreciation to Dr* Qrvis G*
Irwin who directed the study fob his assistance in setting up the
problem* his encouragement during the progress of the study and his
help in preparing the manuscript*
The writer would also like to express her gratitude to
Dr* Paul J. Blommere and Dr* Harold P* Bechtoldt for their assistance
in working out the experimental design and in the statistical analysis
of the data*
The writer is deeply obligated to Mr* Charles Spiker* who
not only assisted in the design for the study but also helped in
securing subjects* assumed full responsibility for the onerous task
of scheduling appointments* and participated in collecting the data*
Perhaps the deepest obligation is to Mrs* Wanda Spiker* v/ho turned
her home into a laboratory for a period of month©* enrolled subjects
in the project* served as an efficient caretaker for sibs who accom*
panied test subjects* and could be depended upon to handle graciously
any situation which might arise* Without her help the project could
not have been completed*
To the parents who enrolled their children in the project
thanks are also due#
TABLE OF CONTENTS
Chapter Page
I, Introduction * * * . * * * « , * . . * * • * • * « * * * * * 1
Statement of the Problem 5
II* Methods and Procedure ?
The Seales Used * . * « « * * * . ►* . • • • • « « « * 7
Subjects 10
Procedure . . « » » • ................. * * * « « < , « * » * « IS
111* Consistency of Performance • » * * , * „ , „ « * « . * < * * IS
Test-retest Reliability of Kuhlmann Scale
for Total Group • * * ; • • * « • * » • • • • « 18
Test-retest Reliability of Cattell Scale
for Total Group « * » * « . » * • * * « * * » « 19
Gattell-Kuhlmann Consistency for Total Group » • • • SO
Consistency of Test Performance as Related
to Examiner * • • .....................• *. «<>* * * » 21
Kuhlmann TesWretest Reliability » » * » « • # » 21
Cattell Test-retest Reliability * * „ * * * * * 21
Cattell-Kuhlmann Consistency * « ' « + • • • • • ZZ
Test~r@test Reliability as a Function of
Scale Order on a Given Bay • • » * « • • • • • • 23
Summary of Findings Regarding Consistency
of Performance 26
PSr. Resultsj Level of Intelligence and Factors
Associated with IQ • » • • « » • » « » » * • • « » * 29
IQ Bifferences Associated with Examiner * * * * * * * 36
Kuhlmann 36
Cattell 39
Summary of Examiner Differences • * • • • » • • 41
Test Performance as a Function of Scale Order • * * * 42
Kuhlmann 43
Cattell * * * * * , * * * » * , . * * « « « « « » 43
Kuhlmann Test-retest Changes * • • ] • » • • • • • • * 45
Cattell Test-retest Changes • • • • • « » * • • • • • 48
Summary of Factors Associated with Obtained IQ's * , 50
V. Discussion » « « » « « * « • * « » * * * * » * « « » * * » « 54
VI* Summary and Conclusions o * * * * * * * * * * * , * * * * 60
Bibliography * * * * „ * , * » « « * * * » * * « * * . * . 66
Appendix A . * * * * * * * * * * * * ' * * * * * * * * * * 67
Appendix 76
i ii
TABLE OF TABLES
Table Fag®
X. Distribution of Kuhlmann Test and Retest IQ’s
According to Sex 3G
II* Distribution of Cattell Test and Retest IQ’s
According to Sex 31
III* Distribution of Differences Between Kuhlmann
and Cattell Test and Retest IQ*s According to
Age Level when Kuhlmann is Subtracted from
Cattell 34
IF. Mean Kuhlmann and Cattell IQ’s and Differences
Between IQ’s on Two Scales on Test and Retest
According to Age Level 35
V* Analysis of Variance Associated with Kuhlmann
IQ’s for Thirty-Two Cases Tested by Two Examiners 59
VI* Analysis of Variance Associated with Cattell IQ’s
for Thirty-Two Cases Tested by Two Examiners 40
VII* Distribution of Differences Between Initial and
Retest Kuhlmann IQ’s According to Age Travel and
Sex when Original is Subtracted from Retest 46
VIII* Analysis of Variance Associated with Kuhlmann IQ’s
for Total Group of Eighty Cases 47
IX* Distribution of Differences Between Initial and
Retest Cattell IQ’s According to Age Level and
Sex when Original is Subtracted from Retest 49
X. Analysis of Variance Associated with Cattell IQ* s
for Total Group of Eighty Cases 51
XI. Basic Data for Study 76
iv
X
Chapter I
INTRODUCTION
Although considerable weight is frequently attached to a
score obtained on a single test, the reliability of tests in current
use for the measurement of intelligence of infants and young children
has not been systematically investigated* C attell (1) and Kuhlmann
(7), both of whom have constructed scales of intelligence covering
the period of infancy and early childhood, represent opposing points
of view*
Cattell, whose scale of infant Intelligence was published in
1940, reported reliability coefficients obtained by the split-half
method of *56, *88, *86, *89, *90, *85, *71 at three, six, nine,
twelve, eighteen, twenty-four, and thirty months respectively* The
reliability coefficient for the S tanford-Binet calculated in the
same way for a sample of the same subjects at three years was *87*
On a basis of these data she concluded (pp. 49-50),
The reliability coefficients of the Infant Tests thus
compare favorably with the Stanford-Binet except at three and
thirty months* No explanation has been found for the lower
reliability coefficient at thirty months unless it be chance
due to the smaller number of cases*
Kuhlmann, on the other hand, (p* 90) refers to the "relative
unreliability of all test scores for young children.11 He implied that
variable performance was to be expected on tests and did not report
the reliability of his scale* He stated (p. 17),
The mathematician has asked for the impossible. To get the
reliability for a test result is a psychological job. And
z
the only way to get it is to discover the effect of the differ
ent factors that enter an examination and then control these
factors or correct the total result for the amount of their
influence* To do this, we must follow the road of controlled
experimental observation of these factors instead of that of
the pencil and paper logician.. .We can make a test reliable so
far as the influence of factors external to the child is con
cerned* But the influence of variable factors in the child
himself are less known and less controllable where known* On
these an endless amount of investigation will be required for
continued progress in making the tests more reliable.
!e have for this and other reasons omitted any attempt to
determine the so-called reliability of the tests selected
for the final scale*
No reports have appeared in the literature regarding the
test-retest reliability of either scale nor the consistency of per
formance on the two scales* With the exception of the 1922 Kuhlmann
revision of the Binet Scale (6)* which is superseded by the 1939
revision, the 1939 Kuhlmann Tests of Mental Development and the
Cattell Infant Intelligence Scale are the only commercially published
scales of intelligence covering the major part of the period of
infancy* ^
Moat studies of other tests purporting to measure the in
telligence of very young children contribute little to the problem
of the consistency of performance of children under two and one half
years of age. Retests, sometimes with the same scale and sometimes
1* The Gesell Developmental Scales (2, 3) are not classified by the
writer as tests of intelligence since Gesell emphasizes that the
developmental quotient yielded by his scales involves a broader
concept than that of intelligence, whereas both Cattell and
Kuhlmann consistently refer to their tests as instruments for
measuring intelligence or mental development.
s
with a different instnaaent, were mad® alter vaiying intervals of time
with emphasis on the predictive value over a period of time. The
reader interested in this aspect of the problem is referred to the
excellent summaries by Qoodenough and Maurer (4) and Maurer (5),
Two studies reported by Goodenough give some idea of the
consistency of performance of preschool age children over relatively
short intervals of time* The reliability of the 1922 Kuhlmann scale
was investigated by intensive study of three groups of Minneapolis
children aged two, three and four years respectively (4). The one
hundred cases included in each age group, equally divided as to sex,
were selected so as to constitute a representative sampling of Min
neapolis population in terns of paternal occupation* Children were
tested on the Kuhlmann scale and retested after an average interval
of 5,9 weeks (range from four to seven weeks). All testing was done
by two exminers. Within each age group, each of the examiners ad
ministered both test and retest to one-fourth of the cases, first
test to one-fourth and second test to one-fourth. Conditions under
which the examinations were administered war© carefully controlled.
Parents observed some but not all of the tests*
The test-retest correlations appear belows
Age Z Age 3 Ag© 4 Total
Boys .810 .817 ,832 .820
Girls .706 .902 *809 .806
Total ,759 .869 ,821 .815
There was a mean gain from test to retest of 3.0 points for the two
year olds, 3.2 points for the three year olds and 6,6 points for the
four year olds* d&in was not related to whether the mother had ob
served the test* so that coaching was not regarded as a factor in the
increased scores.
The consistency of performance of children on two forms of
the Minnesota Preschool scale was studied during the process of stand
ardization and in follow-up studies (5), The standardization sample
was similar to that used in the study of the Kuhlmann in that it was
regarded as representative of Minneapolis population in terras of
paternal occupation. It comprised one hundred cases at each half
yearly age, from eighteen to sixty months. Within each age group,
the sexes wore equally divided and the order in which the two forms
of the tests were administered was counterbalanced. In most cases
the second test was administered the following day* the maximum in
terval between tests was one week. The Minnesota Preschool scale has
both a verbal and performance section, but we are reporting on only
the verbal section, since the non-verbal scale does not extend below
three years of age. The correlation coefficients between the verbal
scores on the two forms of the scale were ,88 for the eighteen month
group, and .92, ,90, .85, .80, ,82, .82, .89, and .85 for succeeding
six month age levels through sixty-six months.
Part of the children were also given the Meriill-Palmer
Scale at ** approximately the same time1* as the Minnesota Preschool
scale. The correlation between the IQ equivalents on the Minnesota
Preschool verbal scale and the Merrill-Palmer scale was .28 for
eighty-nine children under thirty-six months of ag© at time of test,
5
.23 for 178 children between thirty*six and forty-seven months, and
*25 for 240 children over forty-seven months*
Th© results of these studies suggest that under carefully
controlled conditions, groups of children perform quit® consistently
over short intervals of time on the same tests and on different forms
of equated tests but that the degree of consistency is considerably
less when entirely different scales of intelligence are used*
Statement of the Problem
If tests are to be used meaningfully in either a research or
clinical setting, it is essential that th© user have some idea of the
reliability of the measures used and th© comparability of tests pur
porting to measure the same thing* Information is lacking in both of
these areas in regard to the Kuhlmann and Cattell tests of in telli
gence at th© younger age levels*
The present research was undertaken for the primary purpose
of studying the consistency of performance of children between th®
ages of sixteen and thirty months on two different scales of in telli
gence administered on th© same day and given twice within an interval
of one week, as a function of a number of variables* Specific prob
lems to be investigated in this area ares
1* Test-retest reliability of th© 1939 revision of the Kuhlmann
Tests of Mental Development when th© retest is administered
within a two to seven day period following th® first test*
Z» Test-retest reliability of th© Cattell Scale of Infant Intel
ligence under th© same conditions*
