Biostatistics: systematic sampling: practice question

A PSM question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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PSM · Biostatistics: systematic sampling

Sample item

An outpatient register has 1200 patients and a sample of 120 is required by systematic random sampling. How is the sample chosen?

AEvery 10th patient, starting from a randomly chosen number between 1 and 10BEvery 10th patient, always starting from patient number 1C120 patients chosen using a random number table with no intervalDTen patients from each of 120 strata

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

A. Every 10th patient, starting from a randomly chosen number between 1 and 10

The sampling interval is N/n = 1200/120 = 10. A random start between 1 and the interval is chosen and every 10th unit after it is included. The random start preserves the element of chance, and a register arranged in an unrelated order makes the method comparable to simple random sampling.

Option by option

A. Every 10th patient, starting from a randomly chosen number between 1 and 10 (correct)
Correct. Interval 10 with a random start between 1 and 10.
B. Every 10th patient, always starting from patient number 1
A fixed start of 1 removes randomisation and is not random sampling.
C. 120 patients chosen using a random number table with no interval
Choosing numbers from a random table describes simple random sampling, not systematic sampling.
D. Ten patients from each of 120 strata
Taking units from strata describes stratified sampling and the numbers do not fit the design.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

Questions about this PSM question

What is the answer to this PSM question?

The best answer is A, Every 10th patient, starting from a randomly chosen number between 1 and 10. The sampling interval is N/n = 1200/120 = 10.

Why is "Every 10th patient, always starting from patient number 1" not the answer?

A fixed start of 1 removes randomisation and is not random sampling.

Why is "120 patients chosen using a random number table with no interval" not the answer?

Choosing numbers from a random table describes simple random sampling, not systematic sampling.

Why is "Ten patients from each of 120 strata" not the answer?

Taking units from strata describes stratified sampling and the numbers do not fit the design.

What concept does this question test?

It tests Biostatistics: systematic sampling in PSM. A random start between 1 and the interval is chosen and every 10th unit after it is included. The random start preserves the element of chance, and a register arranged in an unrelated order makes the method comparable to simple random sampling.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Biostatistics: systematic sampling?

Practise biostatistics with small calculations until sensitivity, predictive values and risk measures are automatic. Then use the flashcards and the other PSM questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.