5, The researchers cited in the previous problem (Liguori Robinson, 2001) also e

Question

5, The researchers cited in the previous problem (Liguori Robinson, 2001) also examined the effect of caf- and feine on response time in the driving simulator. Ina similar study, researchers measured reaction time 30 minutes after participants consumed one 6-ounce cup of coffee. Using the same driving simulation task, for which the distribution of reaction times is normal with 400 msec and = 40, they obtained a mean of M-392 for a sample of n = 36 participants. a. Are the data sufficient to conclude that caffeine has a significant effect on reaction time? Use a two- tailed test with = .05. b. Compute Cohen's d to estimate the size of the effect. Write a sentence describing the outcome of the hypothesis test and the measure of effect size as it would appear in a research report. c. tor in the north

Explanation / Answer

a) we know that the test statistic is given as

t = (M-Mu)/(sd/sqrt(n))

Putting the values in the formula to calculate the stat as

t = (392-400)/(40/sqrt(36)) = -1.2

also the df = n-1 = 36-1 = 35

and alpha = 0.05 , from the t table the critcal value is

+-2.03

as th t stat is less than the critical value hence we fail to reject the null hypothesis and conclude that caffience doesnt have signficant effect

cohens d is calculated as

Cohen's d = (M2 - M1) SDpooled

SDpooled = ((SD12 + SD22) 2)

d = (392-400)/40

d = -0.2

The effect size is very small , and hence can be considered a small effect size. This means that if two groups' means don't differ by 0.2 standard deviations or more, the difference is trivial, even if it is statistically signficant.

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