28 worksheet t tests chi square continued 1 which

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28 WORKSHEET: T-tests & Chi Square (continued) 1. Which normal curve indicates that the data the greatest variation in its dataset? • Red • Green • Blue • Purple/Violet Which normal curve indicates that the data the least variation in its dataset? • Red • Green • Blue • Purple/Violet Which datasets have the exact same means? Mark all that apply. • Red • Green • Blue • Purple/Violet Which datasets have different means from those in question 3? Mark all that apply. • Red • Green • Blue • Purple/Violet
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Science Research Mentoring Program STATISTICS © 2013 American Museum of Natural History. All Rights Reserved. 29 Session Six: T-tests & Chi Square: ACTIVITY Run a T-test on the Data P R O C E D U R E 1. Please enter your “raw” oak length of leaves measurement data on the board AND your average. Use your own oak data and choose one other data set based on the location opposite yours. 2. In Excel, enter your data in the first column and the second data set in the second column. 3. Chose a blank tile for your T-Test answer. 4. Click on fX and type in ttest and press “go.” T-Test will appear in the lower window, Click OK. 5. Another window appears, enter your first column in Array 1, your second in Array 2, enter 1 in tail, and 1 in type. Click OK. 6. What answer are you getting and what does it mean? 7. Repeat step 3, 4 and 5. But now enter 2 in the tail section. 8. What answer are you getting and what does it mean? When you hit “1” in the tail section, this means are running a one-tail test. You are testing for the possibility of the relationship in one direction and completely disregarding the possibility of a relationship in the other direction. Let’s return to our oak leaves. Our null hypothesis is that the mean is equal to each other, or x. A one-tailed test will test either if the mean is significantly greater than x or if the mean is significantly less than x, but not both. Then, depending on the chosen tail, the mean is significantly greater than or less than x if the test statistic is in the top 5% of its probability distribution or bottom 5% of its probability distribution, resulting in a p-value less than 0.05. The one-tailed test provides more power to detect an effect in one direction by not testing the effect in the other direction.
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Science Research Mentoring Program STATISTICS © 2013 American Museum of Natural History. All Rights Reserved. 30 ACTIVITY: Run a T-test on the Data (continued) S O W H A T D O E S T H E T W O S T A N D F O R ? A T W O -T A I L E D T E S T If you are using a significance level of 0.05, a two-tailed test allots half of your alpha to testing the statistical significance in one direction and half of your alpha to testing statistical significance in the other direction. This means that .025 is in each tail of the distribution of your test statistic. When using a two-tailed test, regardless of the direction of the relationship you hypothesize, you are testing for the possibility of the relationship in both directions. For example, we may wish to compare the mean of a sample to a given value x using a t-test. Our null hypothesis is that the mean is equal to x. A two-tailed test will test both if the mean is significantly greater than x and if
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