M2: sampling methods

• Sampling

  • is a fundamental concept in research, particularly in statistics and social sciences, where researchers need to make inferences about a population based on a smaller subset (or sample) of that population.
  • Rather than studying every individual or item within a population, which can be time-consuming, expensive, or impractical, researchers collect data from a sample that is representative of the larger group.
• Sampling Frame

  • is the term used to mean the list of the members of such population from where you will get the sample.
• 2 CLASSES OF SAMPLING

  1. Probability or Unbiased Sampling
  2. Non-Probability Sampling
• Simple Random Sampling

  • every element of the population has the same probability of being selected for inclusion in the sample.
• Some simple random sampling techniques:

  • Lottery or drawing - with or without replacement
  • Using random numbers
• Systematic Random Sampling

  • a list of randomly arranged elements of the population is used as a sampling frame, and the elements to be included in the sample are selected by skipping through the list at regular intervals.
• Stratified random sampling

  • the population is partitioned into several subgroups or strata, then samples are randomly selected separately from each stratum.
• Cluster or area sampling

  • the population is broken into small groups or clusters, then some of the clusters are randomly selected.
• TYPES OF PROBABILITY SAMPLING

  1. Simple Random Sampling
  2. Systematic Random Sampling
  3. Stratified random sampling
  4. Cluster or area sampling
• TYPES OF NON-PROBABILITY SAMPLING

  1. Quota sampling
  2. Voluntary sampling
  3. Purposive or judgmental sampling
  4. Availability sampling
  5. Snowball sampling
• Quota sampling

  • The researcher divides the population into different subgroups or quotas, usually based on specific characteristics like age, gender, or income.
  • The researcher then selects participants from each subgroup until the quota for that subgroup is met.
  • This ensures that certain characteristics are represented in the sample.

  Example: A researcher might want to sample 100 people, with 50 men and 50 women, to ensure equal representation of gender.
• Voluntary sampling

  • This method relies on individuals volunteering to be part of the sample.
  • The participants self-select, often by responding to a call for participation or an advertisement.
  • While it's easy to implement, it can lead to a sample that may not be representative of the general population.

  Example: A survey posted online, where individuals choose to participate in the research.
• Purposive or judgmental sampling

  • In this type of sampling, the researcher deliberately selects individuals who meet certain criteria or who have specific knowledge or experience relevant to the study.
  • It's a subjective method where the researcher uses their judgment to pick the sample.
• Availability sampling

  • Also known as convenience sampling, this method involves selecting individuals who are easiest to reach or most readily available to the researcher.
  • It's a very convenient method, but it often leads to biased samples since it doesn't represent the entire population.

  Example: A researcher conducting a survey might sample people in their immediate area or workplace because it's convenient, rather than seeking a broader, more representative sample.
• Snowball sampling

  • is used when the population is difficult to access.
  • It starts with a few initial participants, who then refer the researcher to others in the target group.
  • This "snowballs" as more participants are found through recommendations from others in the group.

  Example: A researcher studying a rare disease might begin by interviewing a few patients and ask them to refer others who also have the condition.
• Sample

  • is a subset of the population.

  Example: 1200 voters selected at random for a survey A few cell phones selected for testing Random receipts selected for audit
• Population

  • is the set of all items or individuals of interest.

  Example: All registered voters Cell phones manufactured today Sales receipts for August