Question

A researcher is interested in studying the effect of playing video-games on reaction time. Specifically, he thinks that playing a videogame will change reaction times, but he doesn’t know if it will make subjects faster or slower. He collects the following reaction times (in milliseconds) from a sample of 10 subjects before and after playing a video game for one hour.

Before Playing a Video Game (T1) After Playing a Video Game (T2) Difference Score (D) = T1-T2

360 374

217 254

352   361

399 405

324 370

384 389

307 345

346 377

295 341

386 425

Calculate the Standard Error of the difference scores

2. A researcher decides to study if having a pet leads to lower levels of anxiety. She collects data from a sample of dog owners (n=30) and measures their anxiety levels, which range between 0 and 100. She finds a mean level of anxiety of 68 with a standard deviation of 5. This researcher knows that the mean anxiety level of the population is 60, and wants to compare it to this sample.

Calculate the 95% confidence interval for this test (One-Sample t-Test).

3. A researcher is interested in studying if drinking coffee makes people more or less impulsive (he doesn’t know which). He collects two samples of subjects (100 subjects each) from the same population, one that drinks coffee (group 1) and one that does not (group 2). He measures each on an impulsivity questionnaire, that ranges from 0 (not impulsive) to 100 (very impulsive). He finds that coffee drinkers have an impulsivity of 75, whereas non-coffee drinkers have an impulsivity of 67. He also calculates a standard error of the differences between groups (SE_M1-M2) of 4.08.

Calculate the test statistic (t-score) for this test (Two Independent Samples t-Test).

Answer 1

(1)

T1	T2	d = T1 - T2
360	374	-14
217	254	-37
352	361	-9
399	405	-6
324	370	-46
384	389	-5
307	345	-38
346	377	-31
295	341	-46
386	425	-39
	d-bar =	-27.1
	s =	16.7362

n = 10

Standard error of the difference between means = s/√n = 16.7362/√10 = 5.2925

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