Answer
There is probably a nonresponse effect from the half or more of the original sample that don't respond. A confidence interval does not account for this, as it only accounts for the random variation due to sampling errors. It has to be accounted for in addition to the confidence interval.
Work Step by Step
There is probably a nonresponse effect from the half or more of the original sample that don't respond. A confidence interval does not account for this, as it only accounts for the random variation due to sampling errors. It has to be accounted for in addition to the confidence interval.
