The test-retest method is one way of establishing the reliability of a test. The

Question

The test-retest method is one way of establishing the reliability of a test. The test is administered, and then, at a later date, the same test is re-administered to the same individuals. The correlation coefficient is computed between the two sets of scores. The following test scores were obtained in a test-retest situation. (Give your answers correct to two decimal places.)

(a) Find r.
  

(b) Set a 95% confidence interval for .

First Score 72 67 91 71 96 69 71 62 77 82 Second Score 68 85 65 57 61 78 89 75 82 61

Explanation / Answer

The value of the correlation coefficient r is calculated in the excel

Now, R = -0.52657

The bounds are set as:

Lower bound =

[ (1+R) - (1-R)e2z / sqrt(n-3) ] / [ (1+R) + (1-R)e2z / sqrt(n-3) ]

= -2.4421

Upper Bound

[ (1+R) - (1-R)e-2z / sqrt(n-3) ] / [ (1+R) + (1-R)e-2z / sqrt(n-3) ]

= 0.15418

Hope this helps. Ask if you have any queries.

First Score Second Score 72 68 67 85 Correlation -0.52657 91 65 71 57 96 61 69 78 71 89 62 75 77 82 82 61

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