Question

In a large city school system with 20 elementary schools, the school board is considering the adoption of anew policy that would require elementary students to pass a test in order to be promoted to the next grade. The PTA wants to find out whether parents agree with this plan. Listed below are some of the ideas proposed for gathering data. For each, indicate what kind of sampling strategy is involved and what (if any) biases might result.

a. Put a big ad in the newspaper asking people to log their opinions on the PTA website.

b. Randomly select two of the elementary schools and contact every parent by phone.

c. Send a survey home with every students, and have parents fill it out and return it the next day. Assume all parents submitted a survey.

d. Randomly select 20 parents from each elementary school. Send them a survey, and follow up with a phone call if they do not return the survey within a week.

Answer 1

a.

Sampling Strategy - Voluntary sample because sample is made up of people who self-select into the survey.

Bias - Voluntary response bias because sample members are self-selected

b.

Sampling Strategy - Cluster sampling because sample of clusters (school) is chosen and only individuals within sampled clusters are surveyed.

Bias - Undercoverage - Because of low number of sampled clusters (only two). And parent who are not reachable by phone are inadequately represented in the sample.

c.

Sampling Strategy - Census because all members of the population are included.

Bias - Response bias is possible if the survey has Leading questions. Else would be unbiased.

d.

Sampling Strategy - Stratified sampling with follow-up. because sample consists of random 20 parents from each elementary school (strata) and then a followup for non-response.

Bias - Response bias is possible if the survey has Leading questions. Else would be unbiased.