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A pollster for the Public Policy Institute of California explains how the Institute selects a sample of California adults ("It's About Quality, Not Quantity," San Luis Obispo Tribune, January 21,2000 ): That is done by using computer-generated random residential telephone numbers with all California prefixes, and when there are no answers, calling back repeatedly to the original numbers selected to avoid a bias against hard-to- reach people. Once a call is completed, a second random selection is made by asking for the adult in the household who had the most recent birthday. It is as important to randomize who you speak to in the household as it is to randomize the household you select. If you didn't, you'd primarily get women and older people. Comment on this approach to selecting a sample. How does the sampling procedure attempt to minimize certain types of bias? Are there sources of bias that may still be a concern?

Step by step solution

01

Comment on the use of random phone numbers

First, note that the approach uses computer-generated random residential telephone numbers with all California prefixes. This allows for a random selection of households across California for representation, making it less likely to inherently favor certain groups since every person with a telephone has an equal chance of being chosen.

02

Discuss the attempt to reduce bias against hard-to-reach people

The pollster also mentioned making repeated calls to numbers that do not answer. This is done to minimize a bias against people who may not be home or able to answer the phone during the initial call. So, it works to include a diversity of lifestyles and work schedules in the sample.

03

Comment on the random selection of an adult in the household

By asking for the adult who had the most recent birthday, the sampling procedure randomizes who within the household is chosen to participate. This reduces possible bias towards certain members of the household, such as women and older people who might otherwise be disproportionately represented in telephone surveys.

04

Discuss potential persisting biases

Despite these measures, some possible sources of bias can still be a concern. People without residential telephones or who use only cell phones can't be included in the survey, which could exclude certain socio-economic groups. Plus, people who refuse to participate or continually miss the calls might represent distinct groups and their exclusion could also introduce bias. Lastly, this method assumes that households with more adults have more representation, potentially skewing the results.

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