Sampling Bias Math Example 2

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Example 2

hard
A researcher studies income by sampling shopping mall visitors on weekday afternoons. Identify at least three sources of sampling bias and explain the likely direction of each bias.

Solution

  1. 1
    Bias 1: time-of-day — weekday afternoon visitors are likely unemployed or retired (lower income), excluding working adults who earn more → downward income bias
  2. 2
    Bias 2: location — mall visitors may be middle-income; very poor (can't afford to shop) and very rich (shop elsewhere/online) are underrepresented
  3. 3
    Bias 3: voluntary participation — people who refuse to answer surveys may differ systematically from those who comply (non-response bias)
  4. 4
    Net effect: the sample income distribution is unrepresentative of the broader population in multiple ways

Answer

Three biases: time selection (underrepresents workers), location selection, and non-response bias.
Real sampling bias is usually multifaceted. Researchers must think carefully about who is included, who is excluded, and who refuses to participate. Each source of bias can distort results in different directions, sometimes canceling, sometimes compounding.

About Sampling Bias

Sampling bias occurs when the method of selecting a sample systematically over- or under-represents certain groups relative to their actual proportion in the population.

Learn more about Sampling Bias →

More Sampling Bias Examples

Example 1 medium

A magazine surveys its readers about political preferences and finds 75% support Policy X. Explain w

Example 3 easy

A school wants to know students' favorite lunch option. They survey only students in the cafeteria a

Example 4 hard

An online survey about internet usage gets 10,000 responses. Explain why this large sample does not

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