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In an experiment to learn whether Substance M can help restore memory, the brains of 20 rats were treated to damage their memories. First, the rats were trained to run a maze. After a day, 10 rats (determined at random) were given M, and 7 of them succeeded in the maze. Only 2 of the 10 control rats were successful.

The two-sample z test for "no difference" against "a significantly higher proportion of the M group succeeds":

a) should not be used because the Large Counts condition is violated.

b) gives z = 2.25, P < 0.02

c) gives z = 2.60, P < 0.005

d) should not be used because the Random condition is violated

e) gives z = 2.25, P < 0.04 but not < 0.02

Answer :

Final answer:

A two-sample z-test is used to compare the success rates of two groups of rats in a maze, considering the Large Counts condition and randomness of the experiment. If the z-score is above 1.96, it indicates a statistically significant difference, thus rejecting the null hypothesis. However, actual calculations would need to be performed to give precise z-score and p-value.

Explanation:

When considering whether Substance M can help restore memory in rats and analyzing the experimental data using a two-sample z-test, multiple factors need to be taken into account. The Large Counts condition is a prerequisite for using a z-test, which requires the expected number of successes and failures for each group to be at least 5. Since 10 rats were in the control group and only 2 succeeded, potentially violating this rule, one might argue that a z-test should not be used, as stated in option (a).

Nevertheless, if we proceed with the z-test assuming that the condition is met, the proportions of successes in each group (7 out of 10 for the Substance M group and 2 out of 10 for the control group) would lead to a calculation of a z-score. A z-score above 1.96 suggests that we should reject the null hypothesis, indicating there is a statistically significant difference between the two groups. However, to determine which answer is correct and which z-score and p-value are to be reported (options b, c, and e), we need to perform the actual calculations, which are not provided here.

Furthermore, random assignment is essential to ensure that the results are not biased by any confounding variables, addressing concerns in option (d). Finally, the confidence in the results can be bolstered by comparing them to documented effect sizes and p-values in related studies.

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