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Medical Pearls from the Internet Medical Association

This survey had a 55.6% response rate. 85% of the respondents believed that gun related violence was a public health issue, and 76% believed that gun control laws would help reduce the risk of gun related injuries or death.

Comment: LOW SURVEY RESPONSE RATES: this study demonstrates a common problem when performing a survey -- a low response rate. In general, it is preferred to have a smaller sample with a high response rate (> 80%) than a large sample with a low response rate (< 80%). There is really no satisfactory way to deal with missing data that is not random. With low response rates, there typically is a difference in the two groups: respondents vs non-respondents. For example, people who respond to a survey may be more politically active than those who do not respond. Some research indicates that low response rates do not always lead to significant bias, however, medical journals such at the British Medical Journal still greatly prefer high response rates. One proposed way to conservatively deal with low response rates is to assume non-respondents have a strong bias opposite that of the respondents. In this example, 324 out of 573 people surveyed responded, and 275 of these 324 people believed gun violence is a public health issue. The 99% confidence interval for this proportion of 85% is 71% to 99%. Let us now assume the non-respondents are equally biased in the opposite direction. That is, 85% of the respondents is 35% ABOVE 50%. So for the non-respondents, assume they go the other way, and that this group is 35% BELOW 50%. The result that follows: 275 out of 324 respondents believe gun violence was a public health issue. For the 249 non-respondents, we would estimate that 37 (15%) believed gun violence was a public health issue. Combining these two groups, we find that 312 out of 573 would believe gun violence was a public health issue, which equals 54%. The 95% confidence interval for 312/573 is 44% to 65%. This is a much different conclusion than the authors stated in their article.

Ann Intern Med. 2014 Apr 10    (retrieved Apr, 2014). There are currently 919 pearls in the database. While every attempt has been made to ensure accuracy, mistakes can and do occur. Use databank at your own risk. All pearls © 2020 by the Internet Medical Association. Click Here to view more medical pearls.