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September 23, 2014

September 23, 2014

Posted by **terri** on Tuesday, April 9, 2013 at 11:09am.

- statistics -
**PsyDAG**, Tuesday, April 9, 2013 at 2:43pmI'm not sure what you mean by considering "in groups of 3."

Find the mean first = sum of scores/number of scores

Subtract each of the scores from the mean and square each difference. Find the sum of these squares. Divide that by the number of scores to get variance.

Standard deviation = square root of variance

Z = (score-mean)/SEm

SEm = SD/√n (Are you saying n = 3? If not, n = 5.)

Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the proportion/probability related to your Z scores.

I'll let you do the calculations.

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