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February 29th, 2012, 06:27 PM   #1
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Statistics - chi square

I have a question to do in which the efficacy of a drug used to treat panic disorder is tested. Patients are given a placebo for one week and then the drug for one week, and the number of panic attacks is measured for each week. The data looks like this:

Placebo Drug
0 0
2 1
0 3
1 2
0 0
10 5
2 0
6 4
1 1
1 0
1 3
0 2
3 1
3 1
3 4
4 2
6 4
15 21
28 8
30 0
13 0
15 12
18 18
9 6
8 7
22 14
13 3
12 8
6 7
4 5
0 2

Where each line is a subject and each score is the number of panic attacks experienced that week. I am pretty sure that I need to do a goodness-of-fit chi square test, where my null hypothesis is that the distribution of panic attacks on the drug is the same as (or greater than) the distribution of panic attacks on the placebo. My alternative hypothesis is that the distribution of panic attacks on the drug is less than the distribution of panic attacks on the placebo. I also know that the chi-square test statistic is found by ((O-E)^2)/E.

I'm confused about how to set up my categories to perform the chi-square test. I don't think I'm supposed to use the raw panic attack data shown above because that gives me some divide by zero errors when I try to calculate my test statistic. I tried to create a 2x2 grid (placebo vs. drug by no panic attack vs. panic attack) but that loses information about the number of panic attacks. Any advice?
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March 1st, 2012, 12:33 AM   #2
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Re: Statistics - chi square

Well, what did the problem ask you to do? You're giving a bunch of data but not saying what you are supposed to be doing with it. Chi-square is used for about 3 different things that I can think of off-hand, and none of them seem to fit this. I don't see how goodness of fit applies.

Looks to me like it's a matched sample, but what are you supposed to be doing? The most obvious thing to me is just make inferences about the population using a matched sample t test. (Maybe possibly difference in variance??) I'm not see chi-square in here anywhere, but there may be things chi-square can be used for that I'm not aware of (given it can be used for more than one thing).

It would just help a whole lot to have the instructions and not just the data. Data by itself simply tells you what type of data you have, and not what you want to do with it. Even if it were left up to you to "make some conclusions" with the date, I would think it would still give you an idea of what type of thing you're trying to look for.
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