Reliability refers to how consistent and stable your research results are ,and how well they can be replicated by other researchers. Validity refers to how well your research measures what it intends to measure, and how accurately it reflects the reality of the phenomenon you are studying,

1. DR VANDANA GAUR
ASSOCIATE PROFESSOR
DEPARTMENT OF PSYCHOLOGY

2. INTRODUCTION
• The reliability and validity of a test is important for data collection process.
• Before and after collecting the data , the researcher need to consider the
reliability and validity of their data.
• Reliability- Are we measuring accurately?
• Validity- Are we measuring the right things?

3. RELIABILITY
• It is the degree to which an assessment tool produces stable and
consistent results.
• The extent to which an experiment or measuring procedure yields the
same result on repeated trials
• A measure can be reliable without being valid but it cannot be valid
without being reliable.

4. TYPE OF RELIABILITY
• Test-retest Reliability
• Parallel form Reliability
• Split half or internal Consistency Reliability
• Rational equivalence Reliability

5. TEST-RETEST RELIABILITY
• Obtained by administering the same test twice over a period of time to a group
of individuals.
• The scores are tabulated and the correlation calculated
• Correlation is higher then there will be more reliability

6. PARALLEL FORM RELIABILITY
• Different version of an assessment tool to the same group of individuals
• Both version must contain same construct, skill ,knowledge etc.
• The number of items in both the forms should be the same.
• Distribution of the indexes of difficulty of the items in both should be similar
• Means and SD of both the forms should be equal or nearly so.
• Mode od administration and scoring of both the forms should be uniform

7. SPLIT HALF RELIABILITY
• “Splitting in half” all items of a test that are intended to probe the same area of
knowledge in order to form two “sets” of items
• Items are divided into two halves and then compared. Odd, even items, or 1-50
and 51-100 are two ways to split items.
• Product moment correlation is computed between two sets of scores.
• Spearman-Brown prophecy formula is used for estimating the reliability of the
whole test

8. FACTORS INFLUENCING RELIABIITY
Extrinsic Factors
• Time interval between testing: testing with shorter intervals resulting in the higher
reliability coefficient
• Guessing by the examinee
• Condition under which measure: Favorable conditions will give high reliability
coefficient
Intrinsic Factors
• Length of test: The longer the test, higher the reliability due to the fact that longer test
will provide more adequate sample of the behavior being measured
• Difficulty level of test: tests that are too easy or too difficult for the group members
taking it will tend to provide score of low reliability
• Discrimination value:When the test is composed of discriminating items,the items likely
to be high
• Homogeneity of items:More homogenous more reliabilty

9. • Indicate the degree to which an instrument measures what it is supposed to
measure
• The degree to which a study accurately assesses the specific concept or
parameter that the researcher is trying to measure
• Whether the researcher has measured what it set out to measure
• For a test to be reliable it also need to be valid

10. INTERNAL VALIDITY
• Content or curricular Validity
• Construct validity
• Criterion-related Validity
a- Predictive validity
b-Concurrent validity
EXTERNAL VALIDITY
The extent to which the results of a study are generalizable or transferable

11. CONTENT VALIDITY
• Involves assessing whether the questions asked and the measurement recorded
adequately represent the domains being studied
• Is the questionnaire comprehensive?
• Entire range or universe of the construct is measured
• Usually evaluated and scored by experts in the content area

12. CONSTRUCT VALIDITY
• It implies using the construct correctly
• The most complex type of validity, and involves relating an instrument for data
collection to a theoretical framework
• For example, a researcher inventing a new IQ test might spend a great deal of
time attempting to define intelligence in order to reach an acceptable level of
construct validity.

13. CRITERIAN –RELATED VALIDITY
• Used to product future or current performance
• Demonstrating the accuracy of a measure or procedure by comparing it with
another procedure which has already been demonstrated to be valid
• It correlates test results with another criterion of interest

14. FACTORS AFFECTING VALIDITY
• Range of ability-Like reliability, validity is also influenced by the range of ability of the
sample used. If the subjects have a very limited range of ability, the validiy coefficient
will be low
• Ambiguous direction: If the directions of the test are ambiguous ,the validity of the test
would be lowered
• Socio-cultural differences: Cultural differences among different societies are likely to
affect the validity of a test. However ,when a test is cross-cultural ,this factor does not
affect the validity of the test
• Addition of Inappropriate Items: Inappropriate items are likely to lower both reliability
and validity of the test
• Length of the test: Homogenous lengthening of the test not only increses the reliability
but also validity of the test

15. CONT…….
Environmental factors: Some environmental factors such as room temperature,
lightning and noise can influence the error rate
Research Factors: The researcher can influence the result of the study in many
ways
Instrumental factors: An inadequate sampling of items is the other common
source of instrumentation errors
Subject factors: Any changing physical, emotional or psychological state of the
subject could introduce error into measurement process

16. RELATIONSHIP BETWEEN RELIABILITY AND VALIDITY
Validity and reliability are closely related
• A test cannot be considered valid unless the measurement resulting from it are
reliable
• Likewise result from a test can be reliable and not necessarily valid