The Household sample provides an example of hierarchical data. Unlike the Museum and Short Drinks samples, which are based on real surveys, the Household sample has been created artificially to demonstrate hierarchical data. The Household sample is a small data set that includes a very small number of cases at each level. This is to make it easy to understand what happens when you aggregate the data at the different levels.

The Household sample comes in the following formats:

The Household sample represents the data collected using the following fictitious survey:

Loops called person, trip, and vehicle are used to ask the person, overseas trip, and vehicle questions, respectively. The loops are iterated (and therefore the questions are asked) as many times as necessary. For example, in a household of three people, the person loop will be iterated three times, whereas in a single-person household it will be iterated once. In a household that has no cars, bikes, or other vehicles, the vehicle questions will not be asked at all and the vehicle loop will have no iterations. Click below to see a diagram that provides a representation of the loops and variables in the metadata.

The structure of the tables in the case data in the hierarchical HDATA view of the data corresponds to the structure of the loops in the metadata. This means that because the trip loop is nested within the person loop, the trip table is a child of the person table. The two grids are also represented in the case data by hierarchical tables, each nested within its parent table. Click below to see a diagram that shows the case data for two households (the first and third) represented in the HDATA hierarchical tables. (For simplicity, not all of the variables are shown.)

Notice that there are no trip or vehicle records for the second household that is shown. Click below to see a diagram that shows the relationship of the hierarchical tables .