Transcript Validity and Reliability

Think in terms of ‘the
purpose of tests’ and
the ‘consistency’ with
which the purpose is
fulfilled/met
Validity and Reliability
Neither Valid
nor Reliable
Fairly Valid but
not very
Reliable
Reliable
but not
Valid
Valid &
Reliable
Validity
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Depends on the PURPOSE
E.g. a ruler may be a valid measuring device for
length, but isn’t very valid for measuring volume
Measuring what ‘it’ is supposed to
Matter of degree (how valid?)
Specific to a particular purpose!
Must be inferred from evidence; cannot be directly
measured
Learning outcomes
1.
2.
Content coverage (relevance?)
Level & type of student engagement (cognitive, affective,
psychomotor) – appropriate?
Reliability
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Consistency in the type of result a test yields
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Time & space
participants
Not perfectly similar result but ‘very close-to’
being similar
When someone says you are a ‘reliable’
person, what do they really mean?
Are you a reliable person? 
What do you think…?
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Forced-choice assessment forms are high in reliability, but weak
in validity (true/false)
Performance-based assessment forms are high in both validity
and reliability (true/false)
A test item is said to be unreliable when most students answered
the item wrongly (true/false)
When a test contains items that do not represent the content
covered during instruction, it is known as an unreliable test
(true/false)
Test items that do not successfully measure the intended
learning outcomes (objectives) are invalid items (true/false)
Assessment that does not represent student learning well
enough are definitely invalid and unreliable (true/false)
A valid test can sometimes be unreliable (true/false)
 If a test is valid, it is reliable! (by-product)
Question…
In the context of what you understand about
VALIDITY and RELIABILITY, how do you go
about establishing/ensuring them in your own
test papers?
Indicators of quality
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Validity
Reliability
Utility
Fairness
Question: how are they all inter-related?
Types of validity measures
Face validity
Construct validity
Content validity
Criterion validity
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1.
2.
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Predictive
Concurrent
Consequences validity
Face Validity
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Does it appear to measure what it is supposed to
measure?
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Example: Let’s say you are interested in measuring,
‘Propensity towards violence and aggression’. By simply
looking at the following items, state which ones qualify to
measure the variable of interest:
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Have you been arrested?
Have you been involved in physical fighting?
Do you get angry easily?
Do you sleep with your socks on?
Is it hard to control your anger?
Do you enjoy playing sports?
Construct Validity
Does the test measure the ‘human’
CHARACTERISTIC(s) it is supposed to?
Examples of constructs or ‘human’ characteristics:
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Mathematical reasoning
Verbal reasoning
Musical ability
Spatial ability
Mechanical aptitude
Motivation
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Applicable to PBA/authentic assessment
Each construct is broken down into its component parts
E.g. ‘motivation’ can be broken down to:
Interest
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Attention span
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Hours spent
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Assignments undertaken and submitted, etc.
All of these sub-constructs put together – measure ‘motivation’
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Content Validity
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How well elements of the test relate to the content
domain?
How closely content of questions in the test relates
to content of the curriculum?
Directly relates to instructional objectives and the
fulfillment of the same!
Major concern for achievement tests (where content
is emphasized)
Can you test students on things they have not been
taught?
How to establish Content
Validity?
Instructional objectives (looking at your list)
Table of Specification
E.g.
At the end of the chapter, the student will be able
to do the following:
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1.
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3.
4.
Explain what ‘stars’ are
Discuss the type of stars and galaxies in our universe
Categorize different constellations by looking at the stars
Differentiate between our stars, the sun, and all other
stars
Table of Specification (An Example)
Content areas
Categories of Performance (Mental
Skills)
Knowledge Comprehension Analysis
Total
1. What are
‘stars’?
2. Our star, the
Sun
3. Constellations
4. Galaxies
Total
Grand
Total
Criterion Validity
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The degree to which content on a test (predictor)
correlates with performance on relevant criterion
measures (concrete criterion in the "real" world?)
If they do correlate highly, it means that the test
(predictor) is a valid one!
E.g. if you taught skills relating to ‘public speaking’
and had students do a test on it, the test can be
validated by looking at how it relates to actual
performance (public speaking) of students inside or
outside of the classroom
Two Types of Criterion Validity
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Concurrent Criterion Validity = how well performance
on a test estimates current performance on some valued
measure (criterion)? (e.g. test of dictionary skills can
estimate students’ current skills in the actual use of
dictionary – observation)
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Predictive Criterion Validity = how well performance on
a test predicts future performance on some valued
measure (criterion)? (e.g. reading readiness test might
be used to predict students’ achievement in reading)
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Both are only possible IF the predictors are VALID
Consequences Validity
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The extent to which the assessment served
its intended purpose
Did the test improve performance?
Motivation? Independent learning?
Did it distort the focus of instruction?
Did it encourage or discourage creativity?
Exploration? Higher order thinking?
Factors that can lower Validity
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Unclear directions
Difficult reading vocabulary and sentence structure
Ambiguity in statements
Inadequate time limits
Inappropriate level of difficulty
Poorly constructed test items
Test items inappropriate for the outcomes being measured
Tests that are too short
Improper arrangement of items (complex to easy?)
Identifiable patterns of answers
Teaching
Administration and scoring
Students
Nature of criterion
Reliability
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Measure of consistency of test results from one
administration of the test to the next
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Generalizability – consistency (interwoven concepts)
– if a test item is reliable, it can be correlated with
other items to collectively measure a construct or
content mastery
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A component of validity
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Length of assessment
Measuring Reliability
Test – retest
Give the same test twice to the same group with any
time interval between tests
 Equivalent forms (similar in content, difficulty level, arrangement, type of
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assessment, etc.)
Give two forms of the test to the same group in close
succession
 Split-half
Test has two equivalent halves. Give test once, score
two equivalent halves (odd items vs. even items)
 Cronbach Alpha (SPSS)
Inter-item consistency – one test – one administration
 Inter-rater Consistency (subjective scoring)
Calculate percent of exact agreement by using
Pearson's product moment and find out the
coefficient of determination (SPSS)
How to improve Reliability?
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Quality of items; concise statements,
homogenous words (some sort of uniformity)
Adequate sampling of content domain;
comprehensiveness of items
Longer assessment – less distorted by
chance factors
Developing a scoring plan (esp. for subjective
items – rubrics)
Ensure VALIDITY