Experimental PSY

Question

Rose works for a competing pharmaceutical company testing another drug to treat anxiety. She used the Pearson Correlation formula, which resulted in a .15 with 80 scores. So, this correlation accounts for _________% of the variance. (Fill in the blank.) Is this significant? Why or why not? (Inferential Stats: Effect Size).

r = .15

Answer 1

Hi Constance,

Percentage of variance is expressed by R², which is exactly what it sounds like. R is the Pearson correlation coefficient, R is its square, so percentage of variance is:

0.15² = 0.0225 = 2.25%

Technically, we cannot gauge statistical significance without more information--specifically an ANOVA table-- but an R² that low is unlikely to be significant. Only 2.25% of variability in anxiety scores is explained by the drug. Cohen classifies this percentage as "weak" or "small" depending on regression type, so unlikely to be significant.

I hope this helps.