SAS code for sample sizepower calculation in twosample

• Procedure : power • The TWOSAMPLEMEANS statement performs power and sample size

1. Two-Sample t Test Assuming Equal Variances • You can use the NPERGROUP= option

proc power; twosamplemeans test=diff meandiff = 7 stddev = 12 npergroup =. power

• You can also specify an unbalanced design by using the NTOTAL= and

• Another way to specify the sample sizes is with the GROUPNS= option:

2. Two-Sample Satterthwaite t Test Assuming Unequal Variances • The following statements demonstrate a

Exercise data one; input y type @@; datalines; 65 1 64 2 81 1

proc power; twosamplemeans test=diff meandiff = 2 stddev = 9. 3155 npergroup = 10

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SAS code for sample size/power calculation in two-sample comparisons

• Procedure : power • The TWOSAMPLEMEANS statement performs power and sample size analyses for pooled and unpooled tests, equivalence tests, and confidence interval precision involving two independent samples.

1. Two-Sample t Test Assuming Equal Variances • You can use the NPERGROUP= option in a balanced design and express effects in terms of the mean difference, as in the following statements. Default values for the DIST=, SIDES=, NULLDIFF=, and ALPHA= options specify a two-sided test for no difference with a normal distribution and a significance level of 0. 05. proc power; twosamplemeans test=diff meandiff = 7 stddev = 12 npergroup = 50 power =. ; run;

proc power; twosamplemeans test=diff meandiff = 7 stddev = 12 npergroup =. power = 0. 8; run;

• You can also specify an unbalanced design by using the NTOTAL= and GROUPWEIGHTS= options and express effects in terms of individual group means: proc power; twosamplemeans test=diff groupmeans = 8 | 15 stddev = 4 groupweights = (2 3) ntotal =. power = 0. 9; run;

• Another way to specify the sample sizes is with the GROUPNS= option: proc power; twosamplemeans test=diff groupmeans = 8 | 15 stddev = 4 groupns = (25 40) power =. ; run;

2. Two-Sample Satterthwaite t Test Assuming Unequal Variances • The following statements demonstrate a power computation for the two-sample Satterthwaite t test allowing unequal variances. Default values for the DIST=, SIDES=, NULLDIFF=, and ALPHA= options specify a two-sided test for no difference with a normal distribution and a significance level of 0. 05. proc power; twosamplemeans test=diff_satt meandiff = 3 groupstddevs = 5 | 8 groupweights = (1 2) ntotal = 60 power =. ; run;

Exercise data one; input y type @@; datalines; 65 1 64 2 81 1 71 2 57 1 83 2 66 1 59 2 82 1 65 2 82 1 56 2 67 1 69 2 59 1 74 2 75 1 82 2 70 1 79 2 run; proc ttest data=one; class type; var y; run;

proc power; twosamplemeans test=diff meandiff = 2 stddev = 9. 3155 npergroup = 10 power =. ; run; proc power; twosamplemeans test=diff meandiff = 1 stddev = 9. 3155 npergroup =. power = 0. 9; run;