A researcher studied the effect of an antidepressant on depression.He randomly assigned subjects with moderate levels of depression to two groups.One group received the antidepressant and the other a placebo.Subjects were blinded with respect to the treatment they received.After four weeks, the researcher interviewed all subjects and rated the change in their symptoms based on the comments of subjects during the interview.Critics said that the results were suspect because the ratings were not blind.Explain what this means and how lack of blindness could bias the reported results.