StATS: Injury index creation (September 23, 1999)

Dear Professor Mean, I want to create an injury index that describes the severity of an injury to a child. This would include information about the type of injury, the location of the injury, the age of the child, etc. What's the best way to do this?

It seems to me like you have two choices. First, you can build an index based on your judgment, intuition, and knowledge of medicine. You might let a few graphs and tables of your data give you some guidance, but the predominant emphasis is on what the knowledge and experience that you have accumulated over time. You might get other humans involved by asking them to review and critique your index.

Second, you can let an automated procedure create the index for you. You might tweak things a bit, but the computer does most of the work for you. There are a variety of tools, such as stepwise regression, factor analysis, neural nets, classification and regression trees, and cluster analysis that might help here.

With either approach, of course, you have to take the time to look at validity and reliability. You are probably already more familiar with how to do this than I am.

I would strongly urge you to build your own index rather than letting a machine build it for you. If you don't feel like you know enough to build an index on your own, how will you be able to critically evaluate an index that your automated procedure creates? Also, the number of variables you have is small enough that you can sift through them easily. A lot of these automated procedures shine when you have hundreds or thousands of variables to consider in your index. They also work well when you have thousands or millions of cases to examine. I suspect that your data set is not quite this large.

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