INTRODUCTION
Many professions (business, government, engineering, science, social research, agriculture, etc.) seek the broadest possible factual basis for decision-making. In the absence of data on the subject, a decision taken is just like leaping into the dark. Sampling is a procedure, where in a fraction of the data is taken from a large set of data, and the inference drawn from the sample is extended to whole group. [Raj, p4] The surveyor’s (a person or a establishment in charge of collecting and recording data) or researchers initial task is to formulate a rational justification for the use of sampling in his research. If sampling is found appropriate for a research, the researcher, then:
(1) Identifies the target population as precisely as possible, and in a way that makes sense in terms of the purpose of study.
(2) Puts together a list of the target population from which the sample will be selected. This list is termed as a frame (more appropriately list frame) by many statisticians.
(3) Selects the sample, [Salant, p58] and decide on a sampling technique, and;
(4) Makes an inference about the population.
All these four steps are interwoven and cannot be considered isolated from one another. Simple random sampling, systematic sampling, stratified sampling fall into the category of simple sampling techniques. Complex sampling techniques are used, only in the presence of large experimental data sets; when efficiency is required; and, while making precise estimates about relatively small groups within large populations [In any research conducted, people, places, and things are studied. The opportunity to study the entire population of those people, places, and things is an endeavor that most researchers do not have the time and/or money to undertake. The idea of gathering data from a population is one that has been used successfully over the years and is called a census. This method is mentioned several times in the bible (Wikipedia). It was also used by the Ancient Egyptians “to obtain empirical data describing their subjects” (Babbie 37).
In past years, the idea of collecting data from the entire population was used by political entities to collect opinions about potential political candidates. Census data collection is still very popular for collecting public opinion for political endeavors. For most researchers, however, collecting data from an entire population is almost impossible because of the amount of people, places, or things within the population. Taking a census involves much time and money; something to which most researchers are not accustomed. To collect data on a smaller scale, researchers gather data from a portion or sample of the population.
The purpose of this paper is to describe sampling as a method of data collection.
Probability and non-probability sampling as well as the surrounding validity issues will
be discussed. Sampling theory may be adapted for content analysis, laboratory experiments, and participant observation (Babbie 100). However, this paper will focus on sampling as a method to select participants for surveys; more specifically interviewing and self-administered questionnaires.