Examples
A researcher wants to study all 1,200 students at a high school but surveys only 100 students. What is the population?
All 1,200 students at the high school.
A survey asks students how often they cheat on tests. Some students lie because they're embarrassed. What type of bias is this?
Response bias.
What is the term for collecting data from every member of a population?
A census.
A researcher surveys the first 30 students entering the cafeteria. What sampling method is being used?
Convenience sampling.
A researcher sends a survey to 200 students, but only 50 respond. If the respondents differ from nonrespondents in important ways, what bias may result?
Nonresponse bias.
A researcher randomly selects a starting position on an alphabetical class roster, then chooses every 10th student. What sampling technique is this?
Systematic sampling.
A survey about student sleep habits is posted on Instagram, and students choose whether to participate. What sampling method is used, and what type of bias might occur?
Voluntary response sampling; self-selection bias may occur.
A study about teen social media habits surveys only students who own smartphones, excluding teens without phones. What sampling problem is this?
Undercoverage.
A teacher assigns every student a number and uses a random number generator to choose 20 students. What sampling method is used?
Simple random sampling.
A researcher randomly selects 5 students from each grade to study homework habits. What sampling method is used? Is it a probability or non-probability method?
Stratified random sampling; probability sampling.
A school surveys only varsity athletes to estimate how much exercise all students get. Identify the sampling problem and explain why it affects the results.
Sampling bias, specifically undercoverage. Non-athletes are excluded, making the sample unrepresentative of the school.
A researcher separates students into freshmen, sophomores, juniors, and seniors, then randomly selects students from each grade. What sampling technique is used, and how is it different from cluster sampling?
Stratified random sampling. It selects individuals from every stratum, whereas cluster sampling randomly selects whole groups or clusters.
A school district wants to study student stress across its 10,000 high school students. Researchers randomly select 4 entire high schools and survey every student at those schools. Identify the population, sample, and sampling method.
Population: all 10,000 high school students in the district. Sample: students at the 4 selected schools. Method: cluster sampling.
A researcher emails 500 randomly selected adults about their political opinions. Only 100 respond, mostly people with strong political views. The survey also asks, "Don't you agree that our current leaders are doing a terrible job?" Identify TWO possible sources of bias.
Nonresponse bias, because respondents may differ from nonrespondents, and response bias, because the leading question influences answers.
A university wants to study student satisfaction. One researcher suggests surveying 50 nearby students; another suggests randomly selecting students across all four class years. Which approach is more likely to produce representative results, and what tradeoff does it involve?
Randomly selecting students across all four class years is more likely to be representative. It requires more planning, time, and resources than convenience sampling.