Units and Target Population

The target population is the collective of units about which we would like to draw conclusions. Care needs to be taken in specifying both.

In 1879, Michelson was keen to determine the speed of white light as it travels between any two relatively stationary points in a vacuum. A unit, then, is one transmission of such light between a source and destination, both located in a vacuum. The target population is all such transmissions, before, during and after 1879.

For some investigations it may be easier to define the units or the collective in terms of a process which generates them. An example is a manufacturing process producing units under specified conditions. In such cases it might be more convenient to refer to the target process rather than the target population.