FAQ/Power - CBU statistics Wiki

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Table of sample sizes required for tests of non-zero Kendall, Spearman and Pearson correlations

We assume 90% power and a Type I error of 5%

Null hypothesis : correlation = 0;

Alternative: correlation = non-zero value

If you know the sign of the non-zero correlation the test is one-tailed otherwise it is two-tailed.

Computations using methods in Kraemer, HC & Thiemann, S (1987) How Many Subjects? Statistical Power Analysis in Research. Sage:London.

  • Power calculator also available for the Pearson correlation.

  • Dunlap WP and Myers L (1997) show that for a Pearson correlation, r, 8/$$r^text{2}$$ gives a total sample size with at least 80% power.

Correlations of 0.1, 0.3 and 0.5 correspond to small, medium and high correlations using rules of thumb.

1-tail

2-tail

correlation

Kendall

Spearman

Pearson

Kendall

Spearman

Pearson

0.1

1041

1013

854

1277

1111

1047

0.2

224

250

212

274

307

259

0.3

106

107

93

129

130

113

0.4

58

62

51

70

75

62

0.5

37

39

32

44

46

38

0.6

25

26

21

29

30

25

0.7

18

19

15

21

21

17

0.8

13

<14

<10

15

15

12

0.9

9

<10

<10

11

11

<10

Reference

Dunlap WP and Myers L (1997) Approximating Power for significance tests with one degree of freedom. Psychological Methods 2(2) 186-191.