I have a dataset asking people whether they have been to a certain places (e.g. A, B, C, D), and they can make more than one choice, then a specimen is taken from their nose to see if they are infected with some disease.

I need to find out the relative risk of getting infected for one going to a certain place, I can only think of logistic regression right now, is there any other suggestions?



1 Answer 1


You can still use logistic regression because your outcome is dichotomous, infected vs not-infected. I would just simply take a dummy variable approach and use no travel as the reference category (i.e. for each of your places you have a variable coded as 1 if they visited that place and coded as 0 if they did not visit that place). As such if you transform your beta coefficients to odds (i.e. exponentiate the log odds) the interpretation of the dummy variable for location A would be the odds ratio of visiting location A over not visiting location A controlling for other places one visited. Also note in this approach multi-collinearity is a concern (e.g. if many of the people who travel to A also travel to B it may bias each of their coefficients).

  • 5
    $\begingroup$ This model assumes the response is an additive function of traveling to each place, which is highly unlikely. It can still be made to work by including interaction terms. A full set of all possible interactions might be needed (beyond just the two-way interactions). (That would be mathematically identical to providing a separate dummy for each possible combination of destinations.) $\endgroup$
    – whuber
    Oct 14, 2010 at 4:59
  • 4
    $\begingroup$ Better have a lot of data if you use all interactions (15 parameters) rather than just the main effects (4 parameters)... $\endgroup$ Oct 14, 2010 at 6:56
  • $\begingroup$ @whuber and @Stephen, Thanks for the responses, and I agree completely with each of you. I personally would be ok with the main effects dummy variable approach if multiple responses weren't all that common, which may not be a tenable assumption given the original posters concerns. I would maybe propose other designs if the original poster was interested in the risk of travelling to A vs B (such as some type of matching procedure). And I agree additive risk does not make sense except if some selection bias is occurring. $\endgroup$
    – Andy W
    Oct 14, 2010 at 12:31

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.