Statistics for Life Sciences: Exam 1 Practice Problems

The practice problems were found in the slides.

Researchers want to know how homeowners in Tempe feel about a proposed hazardous waste

site. Tempe’s residential area is divided into 947 blocks, each containing 20 homes. They want a

sample of 300 homes. How can cluster sampling be used?

1. Clusters blocks to make 947 clusters

2. Number the blocks 001 - 947

3. Reduce number of clusters randomly by dividing 300 by 20 to get 15

4. Check answer: 15 × 20 = 300

5. Survey the homes

Researchers want to learn how many hours elementary school students in Phoenix study each

week. There are 21 elementary school districts. Assume each district has 200 registered students.

Explain how to select a sample of 1000 students using cluster sampling.

1. Cluster the schools districts to make 21 cluster

2. number the districts 01 - 21

3. Reduce number of clusters randomly by dividing 1000 by 200 to get 5

4. Check answer: 5 × 200 = 1000

5. Use SRS to select the 5 district and interview 200 students in each district

A town has 250 homeowners: 25 upper income, 175 middle income, and 50 low income. The

town council wants a sample of n = 20 homeowners using stratified sampling with proportional

allocation.

Upper income = 2 students

Middle income = 14 students

Lower income = 4 students

ASU has 80,000 students enrolled: 64,000 undergraduates and 16,000 graduate students. Explain

how to obtain a sample of n = 30 students using stratified random sampling with proportional

allocation.

Undergrad = 24 students

Grad = 6 students

SRS, Cluster, or Stratified? Explain.

Twenty patients (10 randomly chosen male and 10 randomly chosen female) were enrolled in an

experiment to test the e!ectiveness of Tylenol.

Stratified

SRS, Cluster, or Stratified? Explain.

Researchers select 30 individual students, one from each of 30 randomly visited classrooms, to

survey time spent on Facebook.

Cluster

SRS, Cluster, or Stratified? Explain.

Researchers study job satisfaction by interviewing all workers from 5 randomly chosen hospitals.

Cluster

What type of bias is this? Explain.

A political poll is conducted by calling people on landlines

Undercoverage bias; excludes people who do not have a landline

What type of bias is this? Explain.

A political poll is conducted by having listeners call in to a radio program.

Self-Selection Bias; participation is voluntary and open to anyone

What type of bias is this? Explain.

Polls conducted by phone where only 2366/10000 individuals agreed.

Nonresponse Bias; many selected people did not respond

What type of bias is this? Explain.

A political poll asks a specific question whose wording elicits a particular response

Response Bias; the wording elicits a specific response, to the results may not reflect the true feelings of the participants