Systematic sampling

A method of sampling from a list of the population so that the sample is made up of every kth member on the list, after randomly selecting a starting point from 1 to k.

Example

Consider choosing a systematic sample of 20 members from a population list numbered from 1 to 836.

To find k, divide 836 by 20 to get 41.8.

Rounding gives k = 42.

Randomly select a number from 1 to 42 - say, 18.

Start at the person numbered 18 and then choose every 42nd member of the list.

The sample is made up of those numbered:

18, 60, 102, 144, 186, 228, 270, 312, 354, 396, 438, 480, 522, 564, 606, 648, 690, 732, 774, 816

Sometimes rounding may cause the sample size to be one more or one less than the desired size.

Curriculum achievement objectives references

Statistical investigation: Levels 7, 8.

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