A random sample of 49 Kwakiutl native Americans reported that they went fishing an average of 68 days each year. Information from a non-native local population showed that they fished an average of 66 days per year (sd = 14). Do the Kwakiutls fish more than the non-Kwakiutls and if so is it a big difference?
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Concerning the question "is it a big difference" probably your teacher wants you to wrestle with the concept of "effect size", perhaps after testing to see if the difference of 2 days is statistically significant. You can also approach the question of the size of this 2 day (3%) difference by asking questions such as: If the average non-Kwakiutl can feed his/her family by fishing on 66 days, why does it take 68 days for the average Kwakiutl? Are their families larger? Bigger eaters? Do they fish less efficiently? Also, does fish keep for 5 days (365/68 is about 5)? What do the people eat on the days they are not fishing? But if you ask these questions you might find out that the data are hypothetical and there are no answers to these questions. You may just have a hypothetical data set to provide a statistical exercise to help you learn about effect size and/or statistical significance. Look up "effect size" and "statistical significance" in your textbook (if it is not clear, try another textbook). To measure effect size you might use a difference statistic usually denoted by the letter "d". To test for statistical significance you might use a t-test or a z-test. Good luck. |
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