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ACCA Applied Knowledge · Management Accounting · Sampling methods

A cost accountant selects every 20th invoice from a filing system in which invoices are stored in batches of 20, each batch beginning with a large monthly contract invoice. Which problem is most likely to affect this systematic sample?

The likely problem is bias from a periodic pattern. Because invoices repeat in batches of 20 with a large one first, selecting every 20th item could always pick, or always miss, the large invoices, so the sample would not represent the population.

  1. ABias because of a periodic pattern in the populationCorrect
  2. BInability to calculate the sampling interval
  3. CNeed to number every item in a separate random-number table
  4. DOver-representation of small clusters of geographic areas

Explanation

Systematic sampling selects items at a fixed interval. If the population has a repeating pattern that matches the interval, the sample may consistently pick the same type of item (for example always the large contract invoice, or never one). This produces bias. The interval is easily calculated, and no random-number table is needed beyond the starting point.

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