The effect of a new antidepressant drug on reducing the severity of depression was studied in manic-depressive patients at two state mental hospitals. In each hospital all such patients were randomly assigned to either a treatment (new drug) or a control (old drug) group. The results of this experiment are summarized in the following table; a high mean score indicates more of a lowering in depression level than does a low mean score.

a. Without performing any statistical tests, interpret the means in the table.
b. What regression model is appropriate for analyzing the data? For this model, describe how to test whether the effect of the new drug is significantly different from the effect of the old drug.

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Group Hospital Treatment Control n25.Y 8.5.S 1.3 n# 31, r 4.6. S 1.8 25,Y 2,3, S 0.9