The circuit judges in a rural county are considering a change in how jury pools are selected for felony trials. They ask the administrator of the courts to assess the county residents’ reaction to changing the requirement for membership in the jury pool from the current requirement of all registered voters to a new requirement of all registered voters plus all residents with a current driver’s license. The administrator sends questionnaires to a random sample of 1,000 people from the list of registered voters in the county and receives responses from 253 people. What is the population of interest? What is the sampling frame? What possible biases could be present in using the information from the survey?
The circuit judges in a rural county are considering a change in how jury pools are selected for felony trials. They ask the administrator of the courts to assess the county residents’ reaction to changing the requirement for membership in the jury pool from the current requirement of all registered voters to a new requirement of all registered voters plus all residents with a current driver’s license. The administrator sends questionnaires to a random sample of 1,000 people from the list of registered voters in the county and receives responses from 253 people.
- What is the population of interest?
- What is the sampling frame?
- What possible biases could be present in using the information from the survey?
Time magazine, in an article in the late 1950s, stated that “the average Yaleman, class of 1924, makes $25,111 a year,” which, in today’s dollars, would be over $150,000. Time’s estimate was based on replies to a sample survey questionnaire mailed to those members of the Yale class of 1924 whose addresses were on file with the Yale administration in the late 1950s.
- What is the survey’s population of interest?
- Were the techniques used in selecting the sample likely to produce a sample that was representative of the population of interest?
- What are the possible sources of bias in the procedures used to obtain the sample?
- Based on the sources of bias, do you believe that Time’s estimate of the salary of a 1924 Yale graduate in the late 1950s is too high, too low, or nearly the correct value?
A professional society, with a membership of 45,000, is designing a study to evaluate its members’ satisfaction with the type of sessions presented at the society’s annual meeting. In each of the following descriptions of the method of selecting participants in the survey, identify the type of sampling method used (simple random sampling, stratified sampling, or cluster sampling).
- The society has an alphabetical listing of all its members. It assigns a number to each name and then using a computer software program generates 1,250 numbers between 1 and 45,000. It selects these 1,250 members for the survey.
- The society is interested in regional differences in its members’ opinions. Therefore, it divides the United States into nine regions with approximately 5,000 members per region. It then randomly selects 450 members from each region for inclusion in the survey.
- The society is composed of doctors, nurses, and therapists, all working in hospitals. There are a total of 450 distinct hospitals. The society decides to conduct onsite in-person interviews, so it randomly selects 20 hospitals and interviews all members working at the selected hospital.
For each of the following situations, decide what sampling method you would use. Provide an explanation of why you selected a particular method of sampling.
- The major state university in the state is attempting to lobby the state legislature for a bill that would allow the university to charge a higher tuition rate than the other universities in the state. To provide a justification, the university plans to conduct a mail survey of its alumni to collect information concerning their current employment status. The university grants a wide variety of different degrees and wants to make sure that information is obtained about graduates from each of the degree types. A 5% sample of alumni is considered sufficient.
- The Environmental Protection Agency (EPA) is required to inspect landfills in the United States for the presence of certain types of toxic material. The materials were sealed in containers and placed in the landfills. The exact location of the containers is no longer known. The EPA wants to inspect a sample of 100 containers from the 4,000 containers known to be in the landfills to determine if leakage from the containers has occurred.
A medical study is designed to evaluate a new drug, D1, for treating a particular illness. There is a widely used treatment, D2, for this disease to which the new drug will be compared. A placebo will also be included in the study. The researcher has selected 10 hospitals for the study. She does a thorough evaluation of the hospitals and concludes that there may be aspects of the hospitals that may result in the elevation of responses at some of the hospitals. Each hospital has six wards of patients. She will randomly select six patients in each ward to participate in the study. Within each hospital, two wards are randomly assigned to administer D1, two wards to administer D2, and two wards administer the placebo. All six patients in each of the wards will be given the same treatment. Age, BMI, blood pressure, and a measure of degree of illness are recorded for each patient upon entry into the hospital. The response is an assessment of the degree of illness after 6 days of treatment.
Identify each of the following components of the experimental design.
- Factors
- Factor levels
- Blocks
- Experimental unit
- Measurement unit
- Replications
Covariates - Treatments
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