Reliability refers to the consistency of a measure. There are several types of reliability: test-retest, equivalency, inter-rater, and internal consistency. Test-retest reliability assesses consistency over time, equivalency assesses consistency between alternate forms, inter-rater assesses consistency between raters, and internal consistency assesses consistency between items. Factors like memory, practice effects, and maturation can impact reliability over time. Reliability is important for a measure to be valid and useful. Ways to improve reliability include making tests longer, carefully constructing items, and standardizing administration procedures.

1. Reliability
Presented by
Monika Singh
M.Sc.(H.Sc.)

2. Introduction
• In the psychometrics, reliability is the overall
consistency of a measure.
• A measure is said to have a high reliability if
it produces similar results under consistent
conditions.
• For example, measurements of people’s
height and weight are often extremely
reliable

3. Definition of Reliability
• Reliability is defined (Portney and
Watkins, 2000) as:
‘the extent to which a measurement is
consistent and free from error’.

5. Types of Reliability
Test-retest
reliability
Equivalency
reliability
Inter-rater
reliability
Internal
consistency
reliability

6. Test-retest reliability-
• assesses the degree to which test scores are
consistent from one test administration to the next.
• It involves:
Administering a test to a group of individuals
Re-administering the same test to the same group at
some later time
Correlating the first set of scores with the second

7. Test-retest reliability-

8. Assumption of the method
• Number of item in the test are large therefore
memory, practice, and carry over will not effect the
retest scores.
• Innate ability of an individual remains constant so
the growth and maturity will not effect the retest
score.
• Time gap of retest score should not be more than six
month.

9. Advantage
• It is the most simplest and easy method of
estimating reliability coefficient
• It is the most appropriate method of estimating
reliability of speed test but it is adequately used for
speeded test.
• It is an economical method of reliability is one form
of the test is used on both times.

10. Limitation
• This method is less accurate
• It is time consuming method of reliability
• The individual΄s health, emotional condition,
motivational conditions, mental health and mental set
do not remains the same in both the administrations.

11. Equivalency reliability
• assesses the degree to which test scores are
consistent when there is a variation in the methods or
instruments used.
• This method of reliability is known by various name
or terms such as parallel form of reliability ,
alternative forms reliability, equivalent forms of
reliability, and comparable – forms reliability

12. Equivalency reliability

13. • Criteria for Equivalency reliability
The number item should be the same
The item variance should be the same
There should be equivalence with regard to content,
types of items, the range of difficulty value.
Instructional procedure of administering the tests
should be the same

14. Assumption
• The memory, practice and carry over factors do not
effect the scores
• Two forms of a test are virtually alike with reference to;
a) Difficulty and discrimination indexes
b) Content and type of item
c) Size number of items
d) Time of administration

15. Advantage
• The method of reliability is an improvement over the
test retest method of reliability
• The practice, memory, exercise, and maturity effect
are controlled in this method.
• It is an economical and speedy method for
calculating reliability coefficient.
• It is useful for the reliability of achievement tests

16. Limitation
• It is difficult to construct parallel form of test and
satisfy all the conditioned mentioned.
• Interval for administration the two forms will not be
more than two weeks.

17. Inter-rater reliability
• Inter rater reliability is the extent to which
two or more individuals(raters ) agree.

19. Internal consistency reliability
• Internal consistency reliability assesses the consistency of
results across items within a test.
• The most popular method of testing for internal
consistency in the behavioral sciences is coefficient alpha
• There are a wide variety of internal consistency measures
that can be used.
a) Average inter-item correlation
b) Split-half reliability

20. Average inter-item correlation
• Average inter-item correlation is a subtype of internal
consistency reliability.
• It is obtained by taking all of the items on a test that
probe the same construct (e.g., reading
comprehension), determining the correlation
coefficient for each pair of terms, and finally taking
the average of all of these correlation coefficients.

21. Average inter-item correlation

22. Split half method of reliability
• It involves:
Administering a test to a group of individuals
Splitting the test in half in two equal parts
Correlating scores on one half of the test with scores
on the other half of the test
• The common way of dividing the test item is the
odd and even numbers.

24. Spearmen –brown prophecy formula-
R= 2 rxy
1+rxy
R=reliability of whole test
rxy= correlation of x (odd) and y (even) series.

25. Assumption
• It assumes that items of the test is homogeneous. All
the items of the test measure the same trait or ability
• The assumption of for splitting test in to two halves
that these are equivalent

26. Advantages
• All the limitation of earlier methods are eliminated in
this method- memory, carry over, practice skills,
maturity factor.
• When the parallel forms of a test are not advisable
and repetition is not possible, this method is
employed to compute reliability of test.

27. Limitation
• Chance factors may effect scores on the two halves of the
test in the same way; it tends to make the reliability index
too high.
• A test can be divided in two parts in a number of ways, so
that the reliability coefficient is not a unique.
• It is not possible to divide the test in two halves in such a
way that both are equivalent.
• This method cannot be used in power test and
heterogeneous test.

28. Sources of error
Item Sampling
Construction of the Items
 Test administration
Scoring
Difficulty of the Test
Student Factor

29. Factors that contribute to
consistency
• stable characteristics of the individual or the attribute
that one is trying to measure.

30. Factors that contribute to
inconsistency:
• Temporary but general characteristics of the
individual: health, fatigue, motivation, emotional,
strain
• Temporary and specific characteristics of individual:
comprehension of the specific test task, specific
tricks or techniques of dealing with the particular test
materials, fluctuations of memory, attention or
accuracy

31. • Aspects of the testing situation: freedom from
distractions, clarity of instructions, interaction of
personality, sex, or race of examiner
• Chance factors: luck in selection of answers by sheer
guessing, momentary distractions

32. Satisfactory level of reliability
• A satisfactory level of reliability depends on how a
measure is being used.
• The standard is taken from Nunnally (1978), who
suggests that in the early stages of research on predictor
tests or hypothesized measures of a construct, reliabilities
of .70 or higher will be sufficient. scores,
• Nunnally (1978) recommends that a reliability of at least
.90 is desirable, because a great deal depends on the exact
score made by a person on a test.

33. Relationship between reliability
and validity
• Validity and reliability are closely related
• A test cannot be considered valid the measurements
resulting from it are reliable. Likewise, results from a
test can be reliable but not necessarily valid.
• While a reliable test may provide useful valid
information, a test that is not reliable cannot possibly
be valid

35. Ways to improve reliability
• Write longer tests.
• Pay more attention to the careful construction of
the test questions.
• Start planning the test and writing the items well
ahead of the time the test is to be given.
• Write clear directions and use standard
administrative procedures.