Effect Size Measures

d (Cohen)

Verbal description        effect size (d)         % of overlap
Small                                  .20                         85
Medium                              .50                          67
Large                                 .80                          53

Small                                  .20                         85
Medium                              .50                          67
Large                                 .80                          53

Effect size and non-overlapping areas (%) between two pop. distributions

d

% of nonoverlap

0
.1
.2
.3
.4
.5
.6
.7
.8
.9
1.0
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
1.9
2.0
2.2
2.4
2.6
2.8
3.0
3.2
3.4
3.6
3.8
4.0

O
7.7
14.7
21.3
27.4
33.0
38.2
43.0
47.4
51.6
55.4
58.9
62.2
65.3
68.1
70.7
73.1
75.4
77.4
79.4
81.1
84.3
87.0
89.3
91.2
92.8
94.2
95.3
96.3
97.0
97.7

           Cohen, J. (1988). Statistical power analysis for the behavioral sciences (Table 2.2.1 p.22). Hillsdale, NJ: Lawrence Erlbaum.

3.  Significance level vs. Effect Size

 

p

effect size

definition

 

 

 

 

 

effect of sample size  

 

 

 

 
use for comparison purpose  

 

 

 

 

4. Role of significance and sample size in interpreting experimental results

Outcome statistically significant

Sample size

Conclusion

Yes

Yes
 
 

No

No

Small

Large
 
 

Small

Large