Chair and Single Sample

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This week's main DB requires you to answer all of the following questions completely and correctly to receive full credit.

1. A researcher studied the effect of television violence on concentration of a particular blood chemical. In this study, 40 participants were measured over a period of an hour prior to watching a violent show and then immediately after. In the results section, the researcher writes: ʺThere was a significant decline in blood concentration from a mean of 13.41 (SD=2.48) to 12.38 (SD=2.69), t(39)=3.38, p<.01 (one tailed).ʺ Explain this result (including the underlying logic of the computations) to a person who understands hypothesis testing involving a single sample and a known population, but knows nothing about t tests.

2. A psychiatrist hires you to study whether her clients self-disclosed more while sitting in an easy chair or lying down on a couch. All clients had previously agreed to allow the sessions to be videotaped for research purposes. You randomly assigned 10 clients to each condition. The third session for each client was videotaped and an independent observer counted the clientsʹ disclosures. You reported that ʺclients made more disclosures when sitting in easy chairs (M = 18.20) than when lying down on a couch (M = 14.31), t(18) = 2.84, p < .05, two-tailed.ʺ Explain these results to a person who understands the t test for a single sample but knows nothing about the t test for independent means.
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