Is this survey question potentially biasing downstream analyses? I encountered a survey question of this general form (sorry, I have forgotten the citation):

Are you currently taking drug class [X]?

*

*(a) No, and I do not want to take them.

*(b) No, but I want to.

*(c) Yes.


The methods say that youth were also given the option:


*

*(d) Prefer not to answer.


but did not offer this option to adults. So the asymmetry between adult and youth responses is one potential issue.
Another potential issue is how the question only enquires into the participant's desire to take the drug when they are going to respond that they are not currently taking the drug. It certainly seems possible that someone is using a class of drug but doesn't want to, or is using and wants to.
In the study methods they end up encoding "1" for "yes" and "0" for "no", and tie it to a mental health instrument (for depression I believe).
Does the setup of this survey question potentially introduce systematic bias due to the asymmetries noted above?

Potentially yes, if the drug is some sensitive one. Adults may tend to choose (a), so there is some underreporting bias. One possible reason is that the society thinks people who take the drug are bad so people don't want others to know if they take the drug or not. It's likely that there is also a systematic difference between the youth and the adults. Some survey methods can be used to improve the analysis. I suggest trying the survey package in R or Stata.
