What is Reliability?
Reading Reflection Chapter 9
“Reliability”
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Please submit minimum of 250 word statement (APA style) with references (2) regarding this week chapter reading, explain what are some of the important aspects of this week’s reading, provide examples when possible.
Power point with chapter 9 added.
Chapter 9
Reliability
What is Reliability?
Reliability is concerned with questions of consistency
Other terms for reliability are:
Repeatability
Reproducibility
Stability
Consistency
Predictability
Agreement
Homogeneity
Measurement
Measurement is the assignment of number to object or events according to certain rules (Carmines and Zeller, 1979)
Measurement
Measurement is important in quantitative research because:
Quantification allows for powerful statistical analysis
Numbers are often more clearly communicated
Objectivity is increased
Efficiency may be increased
Levels of Measurement
Nominal: a label but nothing more
Categorical: identifies group membership
Ordinal: indicates an order
Interval: also in order but an estimation of distance between the scores
Ratio: order, defined distance, and a zero point
Measurement Error
The sources of error causing unreliability may be one or more of the following:
Measurement is inaccurate or inconsistent
Raters or testers are inaccurate or inconsistent
Measurement Error
The sources of error causing unreliability may be one or more of the following:
Phenomenon being measured varies from one measurement time to the next
The situation is confounding the measurement
Classic Measurement Equation
| X = | t + | e |
| Observed | True | Random |
| Score | Score | Error |
Consistency
In order to maintain consistency of measurement there needs to be:
Interrater reliability
Intrarater reliability
Intercoder reliability
Cohen’s Kappa
A way to calculate the percent of agreement between the two coders
K = fo – fc K = kappa
N – fc fo = frequency of agreement
fc = frequency expected by chance
N = number evaluated
Test-Retest Reliability
A type of reliability that is evaluated by administering the same test to the same people or taking the same measurement on the same people after a specified period of time
The results of the two testing times are then compared statistically
Test-Retest Reliability
Factors affecting the test-retest reliability:
Assumes stability in the phenomenon being measured
May be affected by reactivity
Practice effect may also affect reliability
Test-Retest Reliability
Ways to calculate test-retest reliability include:
Pearson product moment correlation
Intraclass correlations (ICCs)
Homogeneity
Cronbach’s alpha can be used to test the homogeneity of items within a measure
It indicates the extent to which all of the items on the test are “behaving” similarly
Homogeneity
Alpha of 0.70 is acceptable for new measures
Alpha of at least 0.80 is expected for established measures
Higher alphas (at least 0.90 or higher) are desirable for use in clinical evaluation
Reliability of Physical Measures
Systematic error: a consistent error
Random error: inconsistent, unpredictable errors
Random errors can cancel each other out unless the researcher know how to detect them by using the technical error of measurement (TEM)
√ ∑ d2 d = the difference between scores of paired examiners
__________
2 N N = number of pairs of scores
Technical Error of Measurement (TEM)
Improving Reliability
Thoroughly trained raters
Periodic monitoring of raters
Retest and calibrate instruments
Add appropriate items and delete those that lower the alpha coefficient to increase homogeneity
Improving Reliability
Standardize the conditions under which testing is done and minimize any distractions
Make instructions clear, standardized
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