ISCAM
Lab 4

1: Background 2: Files needed 3: Explore the data 4: Thought questions 5: Statistical inference 6: Computer simulation 7: Analysis 8: Conclusions 9: Summary

Statistical Inference

Although it is possible that the dolphin therapy is not more effective and the researchers were unlucky and happened to “draw” more of the subjects who were going to improve into the dolphin therapy group, the key question is whether such an outcome is probable.  But if 13 of the 30 people were going to improve regardless of whether they swam with dolphins or not (the “null hypotheses ”), we would have expected about 6 or 7 of them to end up in each group.  The key question is how unlikely a 10/3 split is by this random assignment process alone.

We will answer this question by replicating the random assignment process all over again, but in a situation where we know that dolphin therapy is not any more effective (assuming the null hypothesis is true).  We’ll suppose we were going to have 13 “improvers” and 17 non-improvers no matter which group they ended up in, and we’ll randomly assign 15 of these 30 subjects to the dolphin therapy group and the remaining 15 to the control group. 

Now the practical question is, how do we do this hypothetical random assignment?  One answer is to use cards, such as playing cards or index cards. 

Gather 30 cards and designate 13 of them to represent improvements (e.g., face cards or red suited cards, blue colored or S-labeled index cards) and then mark 17 of them to represent non-improvements (e.g., non-face cards or black suited cards, green colored index cards or F-labeled index cards).
Shuffle the cards well and randomly deal out 15 to be the dolphin therapy group.
Construct the 2×2 table to show the number of improvers and non-improvers in each group (where clearly nothing different happened to those in “group A” and those in “group B” – any differences between the two groups that arise are due purely to the random assignment process).

(f) Record the results by filling in the Repetition #1 table your lab report and then repeat the process (shuffling and creating a table) two more times and complete two more tables in your lab report.