Systematic sampling and stratified sampling are the types of probability sampling design. Systematic sampling has slightly variation from simple random sampling. Here only the first sampling unit is selected at random and the remaining units are automatically selected in a definite sequence at equal intervals.

When the population to be studied is not homogeneous with respect to a variable or characteristic under study then it is divided into small homogeneous groups called strata. Item within each strata are homogeneous with respect to characteristic under study. From each stratum a simple random sample is selected in proportion to the sample size and the over all sample is obtained by combining the samples for all strata.

When the population to be studied is not homogeneous with respect to a variable or characteristic under study then it is divided into small homogeneous groups called strata. Item within each strata are homogeneous with respect to characteristic under study. From each stratum a simple random sample is selected in proportion to the sample size and the over all sample is obtained by combining the samples for all strata.