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Summary Furr & Bacharach (2014) - Psychometrics An Introduction - Chapter 6 $3.88
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Summary Furr & Bacharach (2014) - Psychometrics An Introduction - Chapter 6

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  • Course
  • Psychometrics: An Introduction (FSWP2052A)
  • Institution
  • Erasmus Universiteit Rotterdam (EUR)
  • Book
  • Psychometrics

Summary study book Psychometrics of R. Michael Furr, Dr. Verne R. Bacharach (H6) - ISBN: 9781452256801, Edition: 1, Year of publication: 2013 (Summary chapter 6)

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  • No
  • H6
  • February 19, 2017
  • 8
  • 2016/2017
  • Summary

Subjects

  • psychologie
  • psychology
  • psychometrics
  • psychometrie
  • furr
  • bacharach
  • erasmus
  • reliability
  • betrouwbaarheid
  • cronbach
  • alpha
  • estimate
  • 25

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  • Erasmus Universiteit Rotterdam (EUR)
  • Psychologie
  • Psychometrics: An Introduction (FSWP2052A)
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Furr, & Bacharach (2014) – Psychometrics An introduction




Chapter 6 – Empirical Estimates of Reliability
- Reliability is theoretical property  only estimate can be made.
- Methods: all from notion of parallel tests, but differ in terms of kind of data that are
available + assumptions on which they rest. BUT: no single method gives completely
accurate estimates under all conditions.

1. Alternate/parallel forms reliability
- Obtaining scores from 2 different form of test  compute correlation between forms
+ interpret this correlation as estimate of reliability. Consistent differences = reliable.
- Only interpret if 2 test forms are parallel: correlation tests = reliability.
o They’re measuring the same set of true scores.
o They have the same amount of error variance.
- Problems:
o Can never truly know if tests are parallel  not sure if both measuring same
psychological attribute = both having same true scores, because contain
different items  correlation not good estimate of reliability.
o Potential for carryover/contamination effects due to repeated testing: taking
one form of test has effect on performance on second form, e.g., memory,
learning, attitudes, mood states, etc.  error scores of both forms are
correlated (COMPARE CTT assumption: error affecting test should be
random/uncorrelated).
- Forms have same means + standard deviations, we think they measure same
construct, then they could be close enough to be parallel  correlation can be used
as estimate of reliability.

Recap: assumptions CTT
- Each observed score is additive function of true scores + error scores (Xo = Xt + Xe).
- True scores are completely identical across 2 forms.
- Error scores sum to 0 for each form.
- True scores are uncorrelated with error scores.
- Error variances are equal for 2 forms.
- Errors of 2 forms affecting test should be random/uncorrelated.
 Both forms equally reliable.

2. Test-retest reliability
- Avoid some problems of alternate forms method + is potentially useful for measures
of stable psychological construct (e.g., intelligence).
o No problem of parallel tests in 2 alternate forms, because same people take
same test on >1 occasion  correlation between 1st test scores + retest scores
can be interpreted as estimate of test’s reliability.
- BUT: applicability also rests on assumptions.
o Stability assumption: participants’ true scores are stable across 2 testing
occasions = being certain true scores don’t change.
o Error variance of 1st test is equal to error variance of 2nd test.
 2 testing occasions must produce scores that are equally reliable; if so, then
correlation = estimate of score’s reliability.

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