CA Foundation · Quantitative Aptitude · Correlation and Regression
In the concurrent deviation method of finding correlation, if each of two series has 11 observations, what value of n is used in the formula r = ±√±(2c − n)/n?
The value of n is 10. In the concurrent deviation method, n is the number of pairs of deviations, which is one fewer than the number of observations. Eleven observations produce ten successive changes in each series, so n equals 10.
- A11
- B10Correct
- C22
- D5
Explanation
Deviations are taken between successive observations, so 11 observations give 10 pairs of deviations. In the formula n is the number of these pairs of deviations, not the number of observations. Using 11 would be the common error of ignoring that the first item has no deviation.
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