The selection probability for each unit equals the specified rate. Systematic random sampling controls the distribution of the sample by spreading it throughout the sampling frame or stratum at equal ...

Depending on the sample size and the values of the size measures, it may be possible for a unit to be selected more than once. The expected number of selections or hits for unit i in stratum h equals ...

With systematic sampling you can then select ... to an environmental factor. For example: 'are more snails found nearer the edges of the lake?' Random sampling would give an estimate of the ...