The list of individuals from which a sample is actually selected is called the sampling frame. Ideally, the frame should list every individual in the population, but in practice, this is often difficult. A frame that leaves out part of the population is a common source of undercoverage.

Step 1: Suppose that a sample of households in a community is selected at random from the telephone directory.

What households are omitted from this frame? Households that do not answer the phone.

Households with unlisted numbers or without telephones.

Households that refuse to take part in surveys.

Households with more than one telephone line.