hen a measure is computed from a sample and therefore used as an index to describe the behaviour of the sample it is

When a measure is computed from a sample and used as an index to describe the behavior of the sample, it is referred to as a statistic. This is a key concept in the field of statistics.

Here are the steps to compute a statistic from a sample:

1. Define the Population: The first step in computing a statistic is to clearly define the population that the sample will be drawn from. This could be anything from the entire human population to a specific group such as women aged 18-24.

2. Draw a Sample: Once the population is defined, a sample is drawn. This should be a representative subset of the population. The method of drawing the sample can vary, but it's important that it's done in a way that doesn't introduce bias.

3. Compute the Measure: The next step is to compute the measure from the sample. This could be a mean, median, mode, standard deviation, etc. The measure that is computed will depend on what you're trying to find out about the population.

4. Use the Measure as an Index: Finally, the measure that was computed from the sample is used as an index to describe the behavior of the sample. This index, or statistic, can then be used to make inferences about the population as a whole.

Remember, the accuracy of the statistic in describing the population will depend on how representative the sample is of the population, and the size of the sample. The larger and more representative the sample, the more accurate the statistic will be.