Posted by
Maguin, Eugene on
Apr 09, 2013; 9:39pm
URL: http://spssx-discussion.165.s1.nabble.com/Program-evaluation-question-tp5719367p5719369.html
There could be a sample problem and there is a statistics problem. The likely sample problem is that some kids' enrollment spanned the program start date, e.g., they were there the year before and the year or two after program start. A clean sample design would drop those kids since they have pre and post data while the rest of the kids have either pre or post data. That's the sample.
Crude methods: Divide the number of incidents by the length of enrollment to get incidents per time period and compare the two groups. That will give you a very rough picture of what the story might be.
Better: To start, I'd guess that the data might conform to a poisson distribution, which I think can be checked in the one of the spss test collections that I seldom need to use. If the data, both pre and post do conform to a poisson distribution, I think but I'm not sure that genlin can be used to analyze the data. And, if not genlin, then genlinmixed. However, you might find that there is an excess of zeros--too many kids not doing anything! There's a number of different models that might be relevant although the one I first think of is a zero-inflated poisson. I don't know whether or not that is available in genlinmixed. I know there are others on the list that have a much broader range and depth of experience with these sorts of data than I do and I hope they will give correct advice where I have failed.
Gene Maguin
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From: SPSSX(r) Discussion [mailto:
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Sent: Tuesday, April 09, 2013 1:13 PM
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Subject: Program evaluation question
This is a program evaluation question.
I have dataset made up incidents at a school between 2006 and 2013. There are just two variables of interest: date of incident e.g., 12/01/2011) and type of incident (e.g., minor injury, physical aggression to staff).
Students stay at the school one to three years. The number of incidents during their stay at the school can vary from 1 to 173. In 2010 a program was instituted at the school to reduce aggressiveness. I’ve recoded type of incident into a new variable named aggress (0 = No, 1 = Yes). The problem I see is that no students have the same number of dates (incidents). How can I evaluate the effectiveness of the program?
Any ideas are more than welcomed.
TIA
Stephen Salbod, Pace University, NYC
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