According to classical test theory, if the observed variance of a test is 50 and the true variance is 40, what is the estimated reliability of the test?

a. 0.40
b. 0.50
c. 0.80
d. 0.90

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50 To calculate the estimated reliability of a test based on classical test theory, you can use the formula:

Reliability = (True Variance) / (True Variance + Error Variance)

In this case, the observed variance of the test is 50 and the true variance is 40.

Error Variance = Observed Variance - True Variance
= 50 - 40
= 10

Now we can calculate the estimated reliability:

Reliability = 40 / (40 + 10)
= 40 / 50
= 0.80

So, the estimated reliability of the test is 0.80.

Therefore, the correct answer is option c. 0.80.