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Reliability and Sampling

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Thus improving reliability can result in improving validity. Let s try another Guess again: What s this? Try again: What is this a picture of? – PowerPoint PPT presentation

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Title: Reliability and Sampling


1
Reliability and Sampling
  • Dennison S. Bhola, Ph.D.

2
What is this a picture of?
3
What is this a picture of?
4
What is this a picture of?
5
What is this a picture of?
6
Do you need more information?
  • Would you be in a better position to identify the
    object if you had more information?
  • Lets see

7
What is this a picture of?
8
What is this a picture of?
9
What is this a picture of?
10
Observation
  • As the amount of information we have increases,
    the reliability of our judgments increases.

11
Observation
  • By improving reliability and focusing on
    important content we can make more accurate
    (valid) decisions.
  • Thus improving reliability can result in
    improving validity.

12
Lets try another
13
Guess again Whats this?
14
Try again What is this a picture of?
15
What is this a picture of?
16
What is this a picture of?
17
What is this a picture of?
18
What is this a picture of?
19
What is this a picture of?
20
Lets try another
The slide contains 3 objects
21
What is this a picture of?
22
What is this a picture of?
23
What is this a picture of?
24
What is this a picture of?
25
What is this a picture of?
26
What is this a picture of?
27
What is this a picture of?
28
What is this a picture of?
29
What is this a picture of?
30
What is this a picture of?
31
What is this a picture of?
32
What is this a picture of?
33
Apple, red ball, tomato
34
Now let us make a connection between reliability
and sampling
  • Each assessment we create contains questions.
  • These questions are a sample of the possible qs
    we can ask in a particular content domain.

35
Reliability and sampling
  • With qs of similar quality
  • the more qs we ask ? the more information we
    gather, and the higher the reliability of the
    assessment.

36
Samples of questions sampling and content
validity
  • Samples that are representative of a population
    allow us to use statistics to make
    generalizations to that population.
  • Keep this in mind when choosing the qs for your
    assessment. A Table of Specifications is useful
    here (more on this later).

37
Samples of people
  • In research we use samples of people from a
    target population, because it is often too costly
    to include the whole population in the study.
  • Samples that are representative of a population,
    allow us to use statistics to make inferences
    about that population.

38
Samples
  • Samples must be carefully selected to be
    representative of the population we want to
    generalize our research findings to.
  • Consider the following scenarios

39
If your sample is made up of 5 volley balls, what
population can you make generalizations to?
40
The 5 volley balls are a good sample for this
population. You could make generalizations to
the volley ball population based on measurements
of the sample.
41
The 5 volley balls are NOT a good sample for this
population. You cannot make generalizations to
this population based on measurements of the
volley ball sample.
42
To make generalizations to the previous
population, this would be a better sample to use.
43
In order to use measurements on a sample to make
generalizations to a population, the sample must
be representative of the population.
44
Reliability of Tests
  • Depends upon
  • The number of good quality test items used
  • more good items provide more information and the
    reliability is likely to improve.

45
Content Validity
  • When you develop a test
  • By design, the test items should sample the
    content domain that you want to make inferences
    about.

46
Inferences
  • In order to make inferences about the content
    domain of interest, the set of items on your test
    must be representative of that content domain.

47
Summary
  • Reliability increases with the number of high
    quality items on an assessment.
  • High quality items provide valuable information
    about student learning.

48
Summary
  • Appropriate sampling of a content domain enables
    us to make inferences about student learning in
    that content domainthis is the essence of
    Content Validity.

49
Summary
  • High reliability combined with appropriate
    sampling of the target content domain are
    important for assessment results to lead to valid
    decisions.
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