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Psychometrics Basics, Study notes of Statistics

Christ UniversityStatistics

- psychometrics - scales of measurement - process of test construction - item analysis

Typology: Study notes

2021/2022

Available from 06/06/2022

s.mukherjee
s.mukherjee 🇮🇳

4 documents

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PSYCHOMETRIC TESTING
An objective resource for identifying and measuring qualities in individuals in order to make
informed decisions
Features –
Measures aspects of mental functions, abilities, preferences
Derived from rigorous, scientific and statistical methods
Objective and standardized
Behavioural characteristics measured
Describes behaviour categorically/numerically
Measures differences across people or across time in the same individual
Purpose –
Classification – belonging to specific category
Self-understanding – source of information
Program evaluation – effectiveness of particular program/intervention
Scientific enquiry
Comparison
Diagnostic assessments
What can be measured? –
Ability
Aptitude
Personality
Motivation
Emotional intelligence
Attitude
Characteristics of a good test –
Objectivity
Practicability
Reliability
Validity
Norms
Classification of tests –
Administrative conditions – individual, group
Scoring – objective, subjective
Time limit in producing response – speed test, power test
Nature of items – verbal, non-verbal, performance, non-language
Purpose or objective – intelligence, aptitude, personality, neuropsychological test,
achievement
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PSYCHOMETRIC TESTING

An objective resource for identifying and measuring qualities in individuals in order to make informed decisions Features –  Measures aspects of mental functions, abilities, preferences  Derived from rigorous, scientific and statistical methods  Objective and standardized  Behavioural characteristics measured  Describes behaviour categorically/numerically  Measures differences across people or across time in the same individual Purpose –  Classification – belonging to specific category  Self-understanding – source of information  Program evaluation – effectiveness of particular program/intervention  Scientific enquiry  Comparison  Diagnostic assessments What can be measured? –  Ability  Aptitude  Personality  Motivation  Emotional intelligence  Attitude Characteristics of a good test –  Objectivity  Practicability  Reliability  Validity  Norms Classification of tests –  Administrative conditions – individual, group  Scoring – objective, subjective  Time limit in producing response – speed test, power test  Nature of items – verbal, non-verbal, performance, non-language  Purpose or objective – intelligence, aptitude, personality, neuropsychological test, achievement

SCALES OF MEASUREMENT

  1. Nominal Scale
    • Applicable for categorical variables
    • Not a measure of quantity
    • Example – eye colour, marital status, country of origin
    • Can compute – frequency distribution
  2. Ordinal Scale
    • Ability to rank in order of magnitude
    • Does not have equal intervals
    • Example – ranking food preferences
    • Can compute – frequency distribution, median, percentiles
  3. Interval Scale
    • Classifies data into groups or categories
    • Designates equal item ordering
    • Possesses equal intervals
    • Lacks true zero point, has arbitrary zero point
    • Example – temperature, IQ
    • Can compute – frequency distribution, median, percentile, addition, subtraction, mean, SD, correlation, regression, ANOVA
  4. Ratio Scale
    • Highest level
    • Has all attributes of interval scale and a true zero point
    • Clearly defines magnitude or value of difference
    • Example – heart beats per minute
    • Can compute – all of the above, ratio

 Put items in present tense  Avoid ambiguous statements  Use short statements not exceeding 20 words  Universals (always, all, none, never) should be avoided  Indefinite qualifiers (only, few, merely) should be avoided  Simple statements, not complex statements  Avoid use of negatives  Be sensitive to cultural and ethnic differences  Correct answer option should not be the longest answer

ITEM ANALYSIS

Computation and examination of any statistical property of an item response distribution Item parameters fall into 3 categories/indices –

  1. That describe distribution of responses to a single item
  2. That describe degree of relationship between the response on the item and some criterion of interest
  3. That are a function of both, meaning relationship to item variance/mean and a criterion of interest Classical Test Theory (CTT) Statistics used –  Correlation – measures how two variables are related  Covariance – how much two random variables vary together  Discrimination index – ability of test to discriminate between different levels of learning  Item difficulty – difficulty level of individual items  Reliability co-efficient – internal consistency of the test  Sample variance/SD – how spread out the scores are  Standard error of measurements – how much measured test scores are spread around a true score Item Analysis using CTT –  Item difficulty – For dichotomous items, its proportion of examinees who correctly answer that item. For polylomous items, its evaluation of mean score. (if p=0.95 the test is very easy, if p=0.35 item is difficult)  Item discrimination – Measured using point biserial correlation which correlates scores on an item to scores on the total test. If the item is strong and measures the topic well, then examinees who get the item right tend to score higher on the test (> 0.20). If its 0.00, item is random data generator and worthless. Difficulty Value (D.V.) Evaluations D. V. Item Evaluation 0.20 – 0.30 Most Difficult 0.30 – 0.40 Difficult 0.40 – 0.60 Moderate Difficult 0.60 – 0.70 Easy 0.70 – 0.80 Most Easy Discrimination Index (D.I.) Guidelines D.I. Item Evaluation

0.40 Very good items 0.30 – 0.39 Reasonably good but subject to improvement 0.20 – 0.29 Marginal items, need improvement <0.19 Poor items, rejected or revised