biased
study conducted by a procedure that tends to overestimate or underestimate the true value
unbiased
study conducted by a procedure that produces the correct result on average
voluntary
people are invited to participate
does not reflect the entire population
self-interest
only give one side (positive) because it is in your best interest
social acceptability
answer in a way that would be less judging
leading question
asking the question to lead toward one answer
nonresponse
people do not respond (non responders)
sampling
some members of the population are more likely to be included in a sample than others