Non-Probability Sampling Techniques
These sampling techniques are more convenient than the techniques discussed on the first page. However, one must note that the data thus obtained is not as reliable or as accurate as the data obtained through probability sampling. In most cases, these techniques are put to use in large scale surveys where it is difficult to use any of the probability sampling techniques, due to unavailability of accurate information about the population. Also, it is important to note here that with these non-probability techniques for sampling, it is quite likely that some elements of the population may not get selected as respondents.
There are again four commonly used non-probability techniques, which are discusses below.
As simple as it sounds, the criteria for selecting the respondents is entirely based on who are readily available or are easy to contact. This technique is so convenient that at times, this is referred to as a convenience technique. Since, this technique involves surveying only those respondents who are easily available; it makes the survey fairly easy and economical to conduct. However, the convenience seriously jeopardizes the reliability of the data obtained.
This is an improvised version of the above technique, which involves fixing up quotas so that the respondents bear some specific characteristics – based on their ratio of existence within the population. For instance – if the population consists of 70% college students and 30% young executives, then the respondents should be picked up in the same ratio from the population.
Purposive or Dimensional Sampling
A further extension of the quota sampling is the purposive technique, which is also commonly referred to as dimensional sampling. It takes into account more than one characteristic and requires that at least some specific percentage of the respondents represent all of these characteristics. For instance – if a survey sets up a 30% quota for respondents who are male, in the age group of 20-25 and unemployed, then if 100 respondents are to be selected for a survey at least 30% of them must hold true to these three characteristics.
This technique works in a very unique way and the sampling begins with the selection of one respondent from the population, based on certain characteristics. This person is then asked to identify the respondents that should be included in the survey. The procedure may be repeated until the desired numbers of respondents have been surveyed.
The researcher has a wide range of sampling techniques to choose from, and the best way to decide on which technique should be used is to keep the desired outcome of the survey in mind.