Lecture 4: Principles of Psychometrics: Reliability II - jhsph ocw
Lecture 4: Principles of Psychometrics: Reliability II - jhsph ocw
Lecture 4: Principles of Psychometrics: Reliability II - jhsph ocw
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Solution 9<br />
Use Spearman-Brown Prophesy Formula<br />
<strong>Reliability</strong> New Scale = N(R)/(1+(N-1)R)<br />
N = (number <strong>of</strong> desired items)/(number <strong>of</strong> items in observed scale)<br />
R = reliability <strong>of</strong> observed scale<br />
For 20 item scale: R = (2*.75)/(1+.75) = .86<br />
For 15 item scale: R = (1.5*.75)/(1+.5*.75) = .82<br />
For 5 item scale: R= (.5*.75)/(1-.5*.75) = .60
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