Populations, Samples, and Observational Units: 10 practice questions

Question 1 of 10

A hospital studies all emergency visits but observes 500 records. Which statement correctly separates the target population from the sample?

1. AThe target population is the full group about which the analyst wants to draw a conclusion, while the sample is the smaller observed group.
2. BThe target population is every row in the available database, and the sample is whichever subset remains after cleaning, even if the database omits entire target groups.
3. CAn observational unit is one cell in a table, while a variable is the row containing all recorded cells.
4. DThe target population and sample become identical once the sample exceeds half of the listed records, regardless of who was excluded from the list.

Question 2 of 10

An electoral register omits unregistered residents. What role does the register play in the sampling process?

1. AThe target population is every row in the available database, and the sample is whichever subset remains after cleaning, even if the database omits entire target groups.
2. BEach repeated visit row is a new independent patient, even when several rows belong to the same person.
3. CThe target population and sample become identical once the sample exceeds half of the listed records, regardless of who was excluded from the list.
4. DA sampling frame is the operational list or mechanism from which units can actually be selected, and it may differ from the target population.

Question 3 of 10

A study analyzes patients, and each patient has three visit rows. What is the distinction between an observational unit and a measured variable?

1. AEach repeated visit row is a new independent patient, even when several rows belong to the same person.
2. BA case or observational unit is the entity from which measurements are collected, and a variable is a characteristic that can vary across cases.
3. CA sample fact is automatically a population fact whenever the sample contains more than one thousand units.
4. DAn observational unit is one cell in a table, while a variable is the row containing all recorded cells.

Question 4 of 10

In a study of patients, each row records one visit. What does the waiting-time value recorded in that row represent?

1. AEach repeated visit row is a new independent patient, even when several rows belong to the same person.
2. BA measurement is the recorded value of a variable for a particular observational unit.
3. CNothing learned from a sample can describe a population under any design, because only a census permits inference.
4. DAn observational unit is one cell in a table, while a variable is the row containing all recorded cells.

Question 5 of 10

Why can a statistic computed from the 500 observed visits differ from the corresponding population parameter?

1. AFacts about a sample are not necessarily facts about the population because samples vary.
2. BA sample fact is automatically a population fact whenever the sample contains more than one thousand units.
3. CNothing learned from a sample can describe a population under any design, because only a census permits inference.
4. DA larger sample from an incomplete frame removes coverage bias because the standard error decreases.

Question 6 of 10

What must connect the target population, operational frame, and selected units before generalizing the result?

1. ACoverage bias disappears once most listed units respond, even if an entire region is absent from the list and the sample remains very large.
2. BInference to a target population requires a defensible link between that population, the sampling frame, and the selection process.
3. CNothing learned from a sample can describe a population under any design, because only a census permits inference.
4. DA sample fact is automatically a population fact whenever the sample contains more than one thousand units.

Question 7 of 10

A survey draws 100,000 addresses from a frame that excludes temporary housing. What problem remains despite the sample size?

1. AFive measurements from each patient create five independent patients, so the record count should be used directly as the independent sample size.
2. BCoverage bias disappears once most listed units respond, even if an entire region is absent from the list and the sample remains very large.
3. CIncreasing the size of a sample from a systematically incomplete frame does not remove coverage bias.
4. DA larger sample from an incomplete frame removes coverage bias because the standard error decreases.

Question 8 of 10

A hospital needs waiting-time precision within two minutes for all shifts; its frame excludes nights, its 2,000 records are daytime-only, and waiting times are highly variable. Which factors determine whether this sample is adequate?

1. AThe adequacy of a sample depends on representativeness, sample size, population variability, and the desired precision of estimates.
2. BCoverage bias disappears once most listed units respond, even if an entire region is absent from the list and the sample remains very large.
3. CCluster membership matters only for the point estimate; uncertainty is unchanged when records from the same cluster are positively dependent.
4. DA larger sample from an incomplete frame removes coverage bias because the standard error decreases.

Question 9 of 10

A device records each of 40 patients once per minute for an hour, the readings are positively correlated, and the target is patient-to-patient variation. Why are 2,400 rows not automatically 2,400 independent units?

1. AWhen several records come from the same person or cluster, the record count is not automatically the number of independent observational units.
2. BTreat positive within-patient correlation as extra independent confirmation.
3. CUse 2,400 as the independent sample size because every stored row contains a distinct measurement.
4. DTreat all minute-level readings as independent because their timestamps differ.

Question 10 of 10

A large weekday sample estimates visits precisely, but its frame omits nights and the target covers all emergency visits. How should the conclusion's scope be stated?

1. AThe conclusion should be narrowed to the observed records only, even after a defensible representative design.
2. BThe conclusion should retain its original population scope even when some target groups had no chance to enter the frame.
3. CThe scope of a conclusion should be narrowed when the observed sample does not represent parts of the intended population.
4. DThe target population and sample become identical once the sample exceeds half of the listed records, regardless of who was excluded from the list.