Measurement of Intelligence

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Measurement of Intelligence

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Measurement of Intelligence




Historical development of mental testing can be divided into three periods for the purpose of convenience.

(A) Pre-Binet Period:

In the 19th century, there was a good deal of interest in the field of psychophysics in which attempts were made to develop general rule of sensory judgement. The functioning of sensory reactions of the typical individuals is actually studied in psycho-physics. Method of limits procedure was used here to measure the extent which people were able to differentiate between stimuli. But the limitation of these experiments was that accurate generalization of the result was not possible.

Francis Galton was the first psychologist who took interest in studying whether individual characteristics are acquired or inherited. For this purpose, he studied the lives of prominent English men and in his book “Hereditary Genius” he demonstrated that personal characteristics, (mental and physical) of men are inherited. He developed a series of tests to measure these characteristics. It was the starting point of mental measurement.

The first laboratory of experimental psychology was established by Wundt in 1879 in Leipzig. He employed two methods to test vision. hearing, reaction time and psychosomatic problems (i) psycho-physical method (ii) Introspection method. He also developed mental tests which could measure

the keenness of vision and hearing, muscular strength, reaction time and other sensory motor functions of the body. Many of Galton’s ideas were brought to the USA by an American psychologist J.M. Catell. Like Galton he also believed that intellectual functions can best be measured by the reaction time and sensory discrimination tests in the last quarter of the 19th century, many psychological laboratories came into existence and studies of individual differences in mental abilities started.

The word “Mental Test” was first used by Catell in 1890 but his tests were actually tests of sensory discrimination, speed of motor responses and the like. Thus, upto this period mental ability was identified as sensory acuity of an individual. The correlation between mental abilities and academic achievements was not known at the time.

Drawbacks of this period:

  • Psychologists were unable to identify and define the nature of intelligence. Keenness of sensory motor reactions were related to intelligence.
  • They were unable to measure the complex functions of the body.
  • Intelligence tests developed during this period were measuring other than intelligence.

(B) Binet Period:

An important incident led the people to think about mental measurement during this period. In the beginning of the 20 century in France, a large number of students failed the examination. For this teachers and students blamed each other. Seeing this, the superintendent of public instruction appointed a committee to devise some techniques to screen out slow learners in the schools. Binet and Simon were among members of the committee. They developed a variety of paper pencil tests in their psychological laboratory established in 1889, to administer them on children of different ages. Through these tests Binet tried to measure more complex mental functions such as power of judgement and reasoning, memory. arithmetic ability, etc.

An important contribution of Binet and Simon is that they categorised their tests in terms of age levels by administering their test items to children of different ages. In this way, an age scale of intelligence was also developed. For example, if an item was correctly answered by majority of seven years old children but only few six years old children could respond it correctly, then this item was reserved for seven years old children. In this way, Binet and Simon developed separate tests for different ages.

 Similarly, if an item suited to eight years old child was correctly answered by a child of 6 years and if the same trend was shown by the six years old child in most of the cases of a test, then the mental age of the child was considered to be eight years not six years, though his chronological age is six years only. Thus, the concept of mental age was also introduced by Binet and Simon for the first time in the history of mental testing and with the help of this concept we could assess the intellectual ability of a person. Some of the tests developed during this period are given below:

Binet-Simon Scale

The first scale of Binet-Simon was published in 1905. This scale consisted of 30 items arranged in increasing order of difficulty. This scale was a crude measure of intelligence of In order of school going children. In to remove some of its defects they revised their scale in 1908. It was the first age based scale and it created a lot of interest among psychologists across the world. The items in the tests were grouped according to the appropriate age levels from 3 to 13 years

Some items for three years age

  • Point to your nose, eyes and mouth
  • Repeat two digits 3. 5.
  • Repeat sentences of six syllables.
  • Enumerate objects in a picture.
  • Give family names. Some items of eight years age
  • Read a passage and remember two lines.
  • Add up the value of five coins. 
  • Name four colours.
  • Count reverse from 20 to zero.
  • Give differences between two objects.

1908 revision of Binet-Simon Scale was adopted by many psychologists of America, Switzerland and Germany and many suggestions were given by them for the improvement of the scale. Binet-Simon accepted their suggestions and revised their scale again in 1911.

Some sample items of 1911 scale are given below:

(A) Age 8 years

  • Gives difference between two objects.
  • Counts reverse from 20 to zero.
  • Points out omissions from unfinished pictures
  • Tells the dates correctly.
  • Repeats the digits.

(B) Age 10 years:

  • Arranges five blocks in order of increasing weights.
  • Reproduces two geometric designs by using memory
  • Criticizes absurd statements 
  • Comprehends and answers difficult questions,
  • Uses three given words in two sentences..

Main Features of Binet-Simon Scale

  1. They are really scales, Le.. items of the tests are arranged in the increasing difficulty order.. Easiest items are put in the beginning and the most difficult item is put in the last. Thus, these scales measure the level or aptitude of an examinee and not their speed.
  2. These tests measure the general abilities of intelligence instead of specific abilities.
  3. They can also measure the mental growth of the subject because they are arranged according to different ages from 3 to 14 years.
  4. They are administered on subjects individually.
  5. Their system of scoring is tied to age norms. A child’s performance on the scale will be compared to that of children of his own age.

L.M. Terman’s revision of Binet-Simon Scale: L.M. Terman of Stanford University revised this scale in 1916 to adapt to American situations. He introduced one new concept which was intelligence Quotient (IQ) in his revision. His scale consisted of 90 items ranging from 3 to 14 years of age. Some items of this scale are given below:

(c) Age 7 years

  • Knows number of fingers on both hands. 
  • Describes pictures.
  • Repeats five digits.
  • Gives differences between paired objects.
  • Ties a bowknot.

1937 Revision of Binet-Simon Scale: Terman along with his associate Merrill revised 1916 scale again in 1937. This revision had two equivalent forms L and M. The number of items in the test was raised to 129 in each L M. form. A new change was also introduced in the test which was the calculation of chronological age. Upto 13 years CA was taken to be as original but after 13 years CA was computed in the following manner.

14 years 13 yrs+2/3 of 14 year 13 ⅔ years

At 15 years 13+2/3 of 2 years 14 1/3 years, 

At 16 years 13+2/3 of 3 years 15 years     

Besides, 16 years was taken to be the list age for calculation of 1Q After that, CA was taken to be constant.

LM form revision of 1960: Binet-Simon scale was last revised in 1960 in which items of both L. and M forms were included in the scale This revision has a range of 2 years of mental age scores to 22 years and 11 months of mental age score. This form of the test measures abilities from categories namely, language, memory, reasoning, social intelligence. conceptual phenomenon, numerical, reasoning and visual motor. Test items are in the form of words, objects and pictures and the responses given by the examinees are in the form of drawing, calculating, writing and speaking. Administration of the test requires one full hour. In this revision intelligence is expressed in terms of standard scores of the deviation IQ 

Wechsler Scale: This scale may be considered an improvement over Binet-Simon scale as it can measure the intelligence of adults very effectively, David Wechsler developed this scale in 1939. This scale was developed in two equivalent forms, each form consisted of ten subtests of which five tests were verbal and five were non-verbal or performance type. This scale was revised in 1955 and was renamed as Wechsler Adult Intelligence Scale (WAIS). It consisted of 11 sub tests of which six were verbal and five were non-verbal. This scale is used on persons above 16 years of age upto 64 and administration time of the scale is one hour. The detail of these 11 subtests are given below:

(a) Verbal subtests:

  • Information: 29 questions are given here to test the recall of knowledge concerning wide varieties of information.
  • Comprehension 14 questions are given here to test understanding of knowledge concerning a particular subject or event.
  • Arithmetic: 14 questions are given here to test numerical ability. These questions are solved orally without using paper and pencil at all. 4. Similarity 13 questions are given here to measure abstract verbal reasoning. Examinees are required here to compare two objects and find out the relationship between
  • Digit span: Memory for digits are measured here. In the first half, the examinee is asked to repeat in the same order, three to nine digits presented in the forward directions and in the second half, the digits are repeated in a backward direction.
  • Vocabulary: 40 words of increasing difficulty value are presented before the examinees here and they are asked to tell the meaning of these wounds

(b) Non-verbal or performance subtests:

  1. Digits symbol nine digits each with different digit symbols are given to the examinees here and they are asked to give the right code for each digit or symbol.
  2. Picture completion: This subtest measures the ability of the examinees to analyse the parts from the whole. Examinees are given 21 cards containing incomplete pictures and they are asked to fill the missing part of each picture. 
  3. Block design Its purpose is to measure the ability to analyse the complex whole. There are only 7 designs in these blocks which have red, white and red-white sides. Examinees are asked to produce a given design with the help of these blocks.
  4. Picture arrangement: Its purpose is to measure the ability to identify the whole from the parts. Here six set of pictures are given to the examinees and they are asked to arrange them in an order which tells a meaningful story. 
  5. Object assembly: Its purpose is to measure the ability to synthesise the whole with the help of parts. Here examinees are given some puzzle pictures each representing some parts of the human body and they are asked to assemble them in the form of a complete man.

Speed and accuracy factors are also scored in Arithmetic, digit symbol, block design, picture arrangement and object assembly. Raw scores of each subject are converted into normalized standard scores with a mean of 10 and SD of 3. This makes the scores of each sub-test comparable. Separate 1Q for verbal and non-verbal subtest forms is calculated by adding up the respective subtests of the two forms and if we add up scores on all the 11 subtests, we obtain total scale score. These standard scores are expressed in the form of deviation IQ with a mean of 100 and SD of 15.

Wechsler developed another scale known as Wechsler intelligence Scale for Children in 1949 to test the intelligence of children from 5 to 15 years of age. It also takes one hour to administer, though there are 12 subtests in this scale. Maze test is the only test which is extra in WISC. Mare subtest has eight mazes to be traced by the examinee with a pencil. These mazes are given in increasing onder of difficulty.

The scoring system of both the tests WAIS and WISC are the same. Here also the total scores are converted into deviation IQ with a mean of 100 and SD of 15.

Advantages of Wechsler Scales

  1. Though Binet’s scale and Wechsler’s scale both are individual scales, yet the later can be administered on small groups of children and adults. 
  2. Wechsler’s scale is easier to administer than and its scoring is also less Binet’s Scale complex than the former.
  3. Wechsler has prepared separate scales for children and adults; Binet’s scale does not possess this advantage.

Other differences of Wechsler Scales and Stanford Binet Scale

  • In Wechsler scale, items are not grouped in terms of mental age as is the case of Stanford Binet scale. Points are given here for all correct responses. Thus, WAIS or WISC is a p is point scale.
  • In Stanford-Binet scale items are interpreted in terms of different age levels of the examinees but in WAIS or WIS similar types of items are grouped together to form subte
  • WAIS has separate age norms for adults but in SB Scale all the individuals above 18 are treated in a similar manner as far as computation of IQ is concerned. Thus, people of all age levels are treated as 18 years of age after 18.
  • In SB tests items are varied, unrelated and upgraded but in WAIS and WISC tests, items are graded according to various range of ages.
  • SB scale is internally standardized and rigid but WAIS is externally standardized and flexible.
  • SB scale refers to qualitative evaluation while WAIS refers to quantitative evaluation.
  • Slight chance of statistical treatment is possible in SB scale but WAIS is fully subject to all statistical analysis.

(c) Post Binet period:

This period is particularly known for testing intelligence in groups and thus group test of intelligence became popular during this period.

A group test i a is one that can be given to a number of subjects at a time by a single examiner, This type of test came into being during first World War for the purpose of classifying soldiers for jobs in accordance with their mental abilities Army Alpha and Army Beta, two tests were developed during this period. Army Alpha is a verbal group test of intelligence meant for literate people. Army beta is a non-verbal group test of intelligence meant for illiterate persons.

We will discuss here some more group test of intelligence:

1. Catell’s Culture Fair Test: This test was developed by RB Catell and was published

by IPAT (Institute for Personality and Ability Testing) in 1961. The test has three scales and can be administered on children and adults both

  • Scale 1 meant for 4-8 years
  • Scale II meant for 8-15 years 
  • Scale III meant for 15 years and above
  1. This test measures the general intelligence factor and takes 30-60 minutes to administer. The test has been prepared in such a manner that previously learnt skill or knowledge does not help the examinee to score more on this test. That is why, it is said to be independent of school achievement, social advantages and environmental influences.
  2. Large Thorndike’s Intelligence Test: This test is meant for primary and secondary school children graded into five different levels. The purpose of the test is to measure verbal comprehension, numerical skill and reasoning abilities. Test has verbal as well as non-verbal items. Only non-verbals items are, however, included at the lower levels. The administration of the test takes 30 minutes in all
  3. Raven Progressive Matrices Test: This test was developed in England. It consists of geometric figures and designs. The subjects find out the relationship between figures and select appropriate parts for completion of each pattern of relations.

Classification of Intelligence Test 

(A) Classification from the point of view of administration 

1. Individual intelligence test: An individual intelligence test is one which is administered to only one person at a time. Binet-Simon is an example.

2. Group intelligence test: A group intelligence test is one which can be administered to more than one person at a time. Army Alpha and Army Beta are two examples of such tests. 

Some general characteristics of group intelligence tests are as follows

  • They have been developed on the assumption that intelligence is a general capacity and can be measured by sampling a variety of mental activities.
  • In group tests the similar types of items are pooled together in different subtests.
  • Every group test is standardized for a special range of ages or school grades.
  • Construction of individual test is also very difficult and costly as compared to group tests. Their scoring and standardization is also time consuming process.
  • It is very difficult to establish rapport between the examiner and the examinees and hence examinees can not be motivated properly in group tests of intelligence. These two limitations are not seen in individual tests.
  • Group tests are superior to individual tests in the sense that norms established here are more dependable than that of individual tests. It is because these norms are calculated on the basis of a very large sample.
  • Individual test provides qualitative performance of the individual while group tests are mostly point scale and express the performance in quantities.

(B) Classification from the point of view of nature of items of the test

1. Verbal test: Verbal test of intelligence is one in which instructions and items are produced before the examinees through the written language. So, examinees must be literate to take these tests. Mohsin’s General intelligence Test, Joshi’s General Mental Ability test and Jalota’s Group General Mental Ability Test are some examples of verbal tests of intelligence of Indian origin.

2. Non-verbal test: A non-verbal test is one which requires the use of language only to impart instructions. The examinees are asked to manipulate the test materials in their own way. Since language is not needed to respond to items here, it can be administered to illiterate persons as well. They are also culturally free and hence they can be applied to any situation representing any culture. Test items are usually of figured relation type. Army Beta. is a good example of a non-language test.

3. Performance test: A performance test is one in which a subject has to perform something or to manipulate some concrete materials. without much use of the language ability, Non-verbal and performance tests are useful for the following groups of people:

  • Deaf and Dumb Those children who cannot hear or speak can be tested with the help of performance test.,
  • Illiterates: Verbal test of intelligence is useless for those who cannot read or write. Performance test is useful for them.
  • Shy children: Many withdrawn children are hesitant to express themselves before others. Performance and non-verbal test of intelligence will suit them very much.
  • Educationally deficient children: Verbal test of intelligence generally measure learning along with intelligence. If children are educationally poor, they will perform poorly on intelligence tests too and thus they will be wrongly declared children of below average intelligence. Such a problem can be overcome by using a performance test or non-verbal intelligence test.
  • Useful for children of other cultures. A particular culture dominates in every verbal intelligence test and thus the test can not be adopted by other cultures. Due to being free from culture, the performance test is suitable for these foreign students. 

Some performance tests of intelligence are given below

(a) Pintner Paterson Scale: This is the first systematic performance test. This scale was standardized in 1917. It consists of 15 subtests.

(b) Goodenough Drawing Test: This scale was developed by Florence Goodenough in 1926. Here child is asked to draw the picture of a man as best as possible without any time limit. This is especially useful for those children who are suspected to be mentally retarted.

Weaknesses of performance test

  • Here the subject can score high due to practice effect and chance success is more frequent than verbal tests. Because of this reason, the reliability coefficient is very low.
  • They fail to distinguish between gifted and average children due to limited scope of these tests,
  • These scales fail to test fine mental abilities such as, ability to make abstraction or concept formation or evaluation abilities of mind.

Interpretation of Intelligence Test Scores: Intelligence test scores can be interpreted in the following three ways:

1. Mental age: This concept was first introduced by Afred Binet of France in 1908. It refers to a score that is determined by comparing a child’s score with the scores obtained by younger or older children in the norming group. Here a child’s score is compared with the average score of his own age. For example, if a 9-year-old child scores 60 on an intelligence test and suppose mental age norms for that scale are as follows:

Mental age of 8 years = 60

Mental age of 9 years = 70

Mental age of 10 years 80

Then, in that case, mental age of the child will be considered as 8 years instead of 9 though his chronological age is 9 years Similarly another child of 8 years obtains a score of 80, then his mental age will be 10 years, though his chronological age is 8 years only.

 Thus, we can say that the mean performance of each age level becomes the mental age for that age level.

2. Intelligent Quotient (IQ): IQ is also based on the concept of mental age. It is the ratio of mental age to the chronological age multiplied by 100

IQ = MA/CA x 100.

Suppose, the mental age of a 10-year-old child is 12 years on the basis of his scores on an intelligence test, his IQ will be

12/10 x 100 =120.

Similarly, if mental age of a person is nine years two months and his age is 12 years 6 months, then his IQ will be

110 /150 x 100 = 73.3.

General classification of persons in terms of IQ

IQ Classification
140 and above Genius
130-140 Very superior
120-130 Superior
110-120 Bright
90-110 Average
80-90 Dull
70-80  Borderline
Below 70 Mentally retarded.

Shortcomings of IQ: Some of the main short

comings of IQ are as follows: 

(i) It is a well-known fact that after 18 years, the mental age of a person tends to stabilize. Thus, if IQ is calculated after this age, the result will be misleading, Le, a person will be less intelligent if he grows in age.

(ii) Variability of IQ scores from one test to another is not the same. As a result IQ scores for different tests would not be directly comparable.

(iii) It has also been found that variability in 1Q scores for the different age levels on the same test is not the same. In that case IQ scores would be a misleading index because it would indicate that a person’s 1Q may increase or decrease as he grows in age. An example will illustrate this point. 

9 years old child12012
7 years old child1209

Here the IQ of 120 of both the children is not the same due to differences in SD.

3. Deviation IQ: Now-a-days IQ ratio is converted into a normalized standard score with a fixed mean of 100 and SD of 15. This is known as DIQ. This fixed mean and SD remain constant through all the age levels. It means that if a child’s score is 1 SD above the mean his DIQ will be 100+ 15 = 115. Similarly, if his score is 1 SD below the meani his DIQ will be 100 15 85 and so on. Thus, with the help of these DIQ scores inter age comparison is also possible.

Uses of Intelligence Test

Intelligence tests can be applied in the following situations, 

1. Measurement of general learning abilities: Intelligence and achievement in schools are highly correlated. If a person is high on an intelligence test, he is expected to score high on school achievements also. Conversely if a person scores high on an intelligence test and still his school achievement is very poor, we can find out other reasons for his educational backwardness.

2. Assessment of individual differences and categorization: With the help of intelligence tests we can categorize a particular class into several convenient groups and plan our instructional strategies accordingly. Thus, intelligence testing is very useful for educational guidance.

3. Exact definition of mental retardation is possible: It is said that those who are below 70 in IQ are retarded but to what extent they are mentally retarded can further be studied with the help of higher screening. We may define the three groups of mentally retarted in the following ways.

CategoryIQ level
IdiotsBelow 25

4. Identification of gifted children

Gifted children are the treasure of society. They must be identified in the earlier stages of their lives so that they can be fully guided and helped for their better advancement which is directly related to the advancement of the society as well. Intelligence testing will help the concerned organisations to chalk out plans in the desired manner. 

5. Vocational guidance: Some children are very forward in verbal abilities and some are superior in non-verbal abilities. This identification is possible only with the help of intelligence tests. Since academic subjects need verbal intelligence and technical subjects need non-verbal or performing abilities, hence children may be guided accordingly.

6. Screening: In today’s age of competition and rush, screening has become a necessity. Every school has limited seats of admission and it has to select only those students who can raise the academic level of the school high and get a name for it. Same is the case with appointments in jobs. For all these purposes, intelligence testing is a must

7. Study of mental growth: Mental abilities develop in a sequential order onward. We can use intelligence tests for studying the trends of mental development of individuals. Intelligence tests have made it clear that mental development of children is a steady consistent process from year-to-year till the age of 25. Intelligence tests show that mind does not develop rapidly in the period of adolescence like the physical and emotional development, but in childhood, it develops rapidly.

Limitations of Intelligence Tests

1. Generally intelligence tests show what a person can do at a certain point of time. These abilities are tested on the basis of certain items included in the test. In order to make the results dependable, a proper size of the sample must be selected for standardization of the test.

2. Some people may be fatigued earlier than others when taking a test. This extent of fatigue may reduce their scores and hence intelligence testing will not be accurate. So scores should be taken with caution.

3. No intelligence test is fully free from cultural influences. So, home or school background may affect the intelligence test scores of subjects

4. Administration of the test also affects the scores of subjects. If proper rapport there between the examiner and the examinee. 10 scores may be high. On the other hand, if children are frightened with the testing situation as is the case of slow learners they will perform poorly on the test. 

5. Taking intelligence scores in absolute form is misleading Intelligence tests do not reveal all the mental abilities in most of the cases. So, intelligence tests must be supplemented with clinical setting and case history methods to collect detailed information about a subject as is done in clinics by physicians who do not entirely believe in physical investigations. He rather takes help of clinical diagnosis before giving remedial treatment to the patients.

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