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« September 26, 2006 | Main | September 28, 2006 »

27 September 2006

Mind the Coding

Here's something new to pick at, in addition to methods problems: coding isues. A recent Science (August 18, 2006, pages 979-982) article by Bruce Dohrenwend and colleagues reported on revised estimates of post traumatic stress disorders of Vietnam veterans. See here for an NYT article. The new study indicates that some 18.7% of Vietnam veterans developed diagnosable post-traumatic stress, compared with earlier estimates of 30.9%. The differences comes mainly from using revised measures of diagnosis and exposure to combat for a subset of the individuals covered in the original data source, the 1988 National Vietnam Veterans' Readjustment Study (NVVRS). The authors added military records to come up with the new measures.

Given the political and financial importance (the military has a budget for mental health), this is quite a difference. One critical issue pointed out by the Science article is that the original study did not adequately control for veterans who had been diagnosed for mental health problems before being sent to combat. Just looking at the overall rates after combat is not a great study design. But this also makes me wonder about how the data was collected in the first place. Maybe the most disabled veterans didn’t reply to the survey, or were in such state of illness that they couldn’t (or had died of related illnesses). The NVVRS is supposedly representative but this would be an interesting point to examine.

This article also illustrates how important the data, measures and codings are in social science research these days. It seems that taking these issues more seriously should be part of the academic and policy process just like replication should be (see here and here for some discussion this issue). While study and sample design are under much scrutiny these days, there are still few discussions about the sensitivity to coding and data. Given the difference they can make, this should change.

Posted by Sebastian Bauhoff at 11:00 PM