The primary sampling is habitually done to warrant that the study populace that is being researched is accurately sampled while the study sample is equitably disseminated. In other words, the distribution of the sample within the population is fair. Moreover, the preliminary testing or previous sampling is useful in avoiding the problem of collecting large sets of data that would not be useful at the end of the survey. Collecting useless data may result from improper sampling preparation, preservation, or ineffective methods of sampling. Preliminary sampling prevents situations where the target population could easily be missed.
Preliminary sampling is the method used to get the auxiliary information that would be utilized to attain more efficient sampling as well as the estimation procedures. Moreover, preliminary samples are better used, especially where there is the unavailability of prior information about the entire population. The information attained through preliminary sampling is then used to estimate the smaller and final sample. Generally, the information gotten through the preliminary sample for sampling purposes is used to change the selection of probabilities, group the units, and for the direct use in forming the estimates.