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
- What is your computed answer? tobs = 1.315
- 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.
- 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.
- 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.
- What were your degrees of freedom? N-1 = 9
- 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.
- 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).
- 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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