Natural Resource Biometrics

Unit Expansion in Sampling

The idea of an expansion factor is the sample area may be convenient for sampling but makes little sense in reporting. We need a conversion factor to change the sample area to the reporting unit. Common reporting units include:

• acre.
• hectare.
• square mile.
• square kilometer.
• day.
• year.

We usually sample in fractional units of these reporting units. When we are using Probability Proportional to Frequency (PPF) the expansion is the fractionali of the area of the sample, in relation to reporting unit.

Here is an example, if we sample a plot that is 1/4 of an acre. We assume that the plot is representative, of the unsampled trees on the acre. Therefore, we multiple the 1/4 acre sample by 4 to get thei trees per acre.

This concept works the same with other units. For example, we can sample conduct a time sample of 15 minutes. If our reporting unit is a hour the expansion factor is 4 as there are 4 15 minute time periods in 1 hour or 60 minutes.