Which sampling method involves selecting the first item at random and then every nth item thereafter?

Which sampling method involves selecting the first item at random and then every nth item thereafter?

• A. Random
• B. Systematic - random selection of first item and every nth item
• C. Haphazard
• D. Block selection, e.g. sales invoices in July

Answer: (B)

This method is systematic sampling with a random start. You begin by selecting a random starting position in the population list, then choose every nth item after that fixed interval. It provides a spread across the entire population and is efficient for choosing a representative sample without needing a fresh random draw for every item. However, beware that if the data have a hidden pattern that repeats at the chosen interval, bias can creep in. The other approaches don’t fit: random sampling would give each item an equal chance without a fixed gap; haphazard selection is informal and lacks a defined interval; block selection collects contiguous items in a block rather than items spaced at regular intervals.

This method is systematic sampling with a random start. You begin by selecting a random starting position in the population list, then choose every nth item after that fixed interval. It provides a spread across the entire population and is efficient for choosing a representative sample without needing a fresh random draw for every item. However, beware that if the data have a hidden pattern that repeats at the chosen interval, bias can creep in.

The other approaches don’t fit: random sampling would give each item an equal chance without a fixed gap; haphazard selection is informal and lacks a defined interval; block selection collects contiguous items in a block rather than items spaced at regular intervals.