Assume that I have just conducted a study comparing cognitive development of lowbirthweight (premature) and normal-birthweight babies at one year of age. Using a score of my own devising, I found the sample means of the two groups to be 25 and 30, respectively, with a pooled standard deviation (sp) of 8. There were 20 subjects in each group. If we assume that the true means and standard deviations have been estimated exactly, what was the a priori probability (the probability before the experiment was conducted) that this study would find a significant difference?
Answer to relevant QuestionsLet’s modify Exercise 15.12 to have sample means of 25 and 28, with a pooled standard deviation of 8 and sample sizes of 20 and 20. (a) What is the a priori power of this experiment? (b) Run the t test on the data. (c) ...Generate a table analogous to Table 15.2 for power equal to 0.60, with a = .05, two-tailed. In Exercise 15.3 what sample sizes would be needed to raise power to 0.70, 0.80, and 0.90? The data in Exercises 16.7 and 16.9 both produced a significant F. Do you have more or less faith in one of these effects? Why? What effect does smoking have on performance? Spilich, June, and Renner (1992) asked nonsmokers (NS), smokers who had delayed smoking for three hours (DS), and smokers who were actively smoking (AS) to perform a pattern ...
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