When you want to size the sample size, the procedure proceeds in three distinct steps:

1. Evaluate the data collection instrument and judge the most important variable of the questionnaire or the most significant group of variables;

2. Analyze if it is ordinal, interval or nominal;

3. Check if the population is finite or infinite;

Interval variable and infinite population | |

Interval variable and finite population | |

Nominal or ordinal variable and infinite population | |

Nominal or ordinal variable and finite population |

Note: The proportion (p) will be the estimate of the true proportion of one of the chosen levels for the adopted variable. For example, 60% of the sample phones is Nokia, so p will be 0.60.

The ratio (q) will always be 1 - p. In this example q, will be 0.4. The error is represented by d.

For cases where the proportions cannot be identified, 0.5 is given for p and q.

Next: Data Types