Seminar aus Statistik für das Magisterstudium - Example 7.4

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The following data are given by Moss et al (1992) for the somatostin-immunoreactive cell density before and after eradication of H. Pylon using DeNol. If a new cross-over study was planned with 15 patients, what effect size could be detected with 80% power and 2-sided 5% significance?

> comb = expand.grid(power=c(.8,.9),alt=c("one", "two"))
> data.frame(comb,
+            n=apply(comb, 1, function(r)
+                                ceiling(power.t.test(delta=10,
+                                                     sd=10,
+                                                     power=as.numeric(r[1]),
+                                                     type="paired",
+                                                     alt=r[2])$n)))
  power alt  n
1   0.8 one  8
2   0.9 one 11
3   0.8 two 10
4   0.9 two 13