bias and sampling This was an interview question I encountered. can some one answer this
When you sample, what bias are you inflicting? How do you control for biases?
 What are some of the first things that come to mind when I do X in terms of biasing your data?
 A: The type of bias will depend on the type of sample.  Simple random samples ought not impose any bias.
However, depending on the context, SRS may be impossible.  You didn't say what job you were interviewing for, so it's hard to know what sort of example to give.  But suppose you are doing a political poll.  No matter what method you use (phone, internet, mail, in-person), not everyone you ask will answer and not everyone who answers will do so honestly. E.g. some people will try to guess what the interviewer wants to hear and give that answer (I remember one study that found that, if the person asking the questions had a southern accent, the answers were more likely to be racist - fascinating set of biases there!) 
If you are asking about stigmatized behavior, people will (in most cases) underestimate it.
If you ask about drug adherence, people will over estimate.
Then there are all the non-SRS methods of sampling (cluster sampling, stratified sampling, snowball sampling and many many more).
As to what could be done.... That depends hugely on the field you are in.
A full answer to this question would be several books long. 
