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|
|Mean = 8.6||Mean = 7.6||D = 10||D2 = 62|
|S = 3.306559138 ||S = 3.169297153|
|S2 = 10.933333333||S2 = 10.044444444|
- 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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