Research Sampling

Interactive Infographic: Probability Sampling Methods Non-Probability Sampling Methods

Research Methodology

Regina Moreno | 41947Fernando Teran | 41907

Methods of sampling from a population. (2018, August 20). Healthknowledge.org. Retrieved October 15, 2020, from https://www.healthknowledge.org.uk/public-health-textbook/research-methods/1a-epidemiology/methods-of-sampling-population

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Probability Sampling Methods

In probability (random) sampling, you start with a complete sampling frame of all eligible individuals from which you select your sample. In this way, all eligible individuals have a chance of being chosen for the sample, and you will be more able to generalise the results from your study. Probability sampling methods tend to be more time-consuming and expensive than non-probability sampling.

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Examples

Say we select a sample of 100 students from a school with a population of 1,000 students; by dividing the total population by the desired sample size to get an interval of 10, then randomly selecting a number between 1 and 10 as the starting point to select every 10th student until a sample of 100 is obtained. In order to conduct a survey of 1,000 households in a city with a total of 10,000 households, systematic sampling can be used by dividing the total population by the desired sample size to get an interval of 10, randomly selecting a number between 1 and 10 as the starting point, and then selecting every 10th household until a sample of 1000 is obtained. Systematic sampling can be used to conduct a study on the usage of social media among university students by obtaining a list of all the students in the university, selecting every nth student on the list using an interval of 20 (for example), and randomly selecting a starting point between 1 and 20. Then, every 20th student on the list can be selected until a sample of 500 is obtained from a population of 10,000 students.

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Non-Probability Sampling Methods

In non-probability (non-random) sampling, you do not start with a complete sampling frame, so some individuals have no chance of being selected.Consequently, you cannot estimate the effect of sampling error and there is a significant risk of ending up with a non-representative sample which produces non-generalisable results. However, non-probability sampling methods tend to be cheaper and more convenient, and they are useful for exploratory research and hypothesis generation.

80%

of what we do and see, we remember.

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Examples

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A college professor conducting a survey of their students in class and only collecting responses from those who volunteer to participate. A market researcher conducting a survey on shopping habits by approaching customers at a shopping mall and only collecting responses from those who agree to take the survey. A fast food restaurant conducting a taste test of a new menu item by only inviting their regular customers who are already in the restaurant at a particular time.