## Practice Problems: t-tests

A researcher hypothesizes that electrical stimulation of the lateral habenula will result in a decrease in food intake (in this case, chocolate chips) in rats. Rats undergo stereotaxic surgery and an electrode is implanted in the right lateral habenula. Following a ten day recovery period, rats (kept at 80 percent body weight) are tested for the number of chocolate chips consumed during a 10 minute period of time both with and without electrical stimulation. The testing conditions are counter balanced. Compute the appropriate t-test for the data provided below.

 Stimulation No Stimulation D D2 12 8 4 16 7 7 0 0 3 4 -1 1 11 14 -3 9 8 6 2 4 5 7 -2 4 14 12 2 4 7 5 2 4 9 5 4 16 10 8 2 4 Mean = 8.6 Mean = 7.6 D = 10 D2 = 62 S = 3.306559138 S = 3.169297153 S2 = 10.933333333 S2 = 10.044444444

### Correlated t-test

2. What would be the null hypothesis in this study? Electrical stimulation of the lateral habenula has no impact on food intake; there will be no difference in the amount of chocolate chips consumed.

3. What would be the alternate hypothesis? Electrical stimulation of the lateral habenula will have an impact on food intake either increasing or decreasing the amount of chocolate chips consumed.

4. What probability level did you choose and why? .05 There is little risk involved if either a Type I or a Type II error is made.

5. What were your degrees of freedom? N-1 = 9

6. Is there a significant difference between the two testing conditions? There is no significant difference between the amount of chocolate chips consumed. The tobs fall in the middle section of the t-distribution.

7. Interpret your answer. Electrical stimulation appears to have no impact on the amount of chocolate chips consumed by the rat (t=1.315, not significant).

8. If you have made an error, would it be a Type I or a Type II error? Explain your answer. If an error was made, it would have to be a Type II error as we found no differences. It may be that the lateral habenula does play a role in food intake but we failed to demonstrate it with this study/sample.

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