Lesson 3

• Population


  An entire group that is under study or investigation
• Sample


  A subset taken from a population, either by random or non-random sampling techniques
• Random sample


  A selection of n elements derived from a population N, in which each sample point has an equal chance of being selected using an appropriate sampling technique
• Lottery sampling


  1. Every member of the population has an equal chance of being selected

  2. Names represented by small pieces of paper, mixed together and picked out at random

  3. Selected members included in the sample
• Systematic random sampling


  1. Members of the population are listed and samples are selected in intervals called sample intervals

  2. Every nth element from a list is selected from a randomly selected starting point
• Stratified random sampling


  1. Members of the population are grouped based on their homogeneity

  2. Population classified into subpopulations or strata based on characteristics

  3. Selection of elements made separately from within each stratum, usually by random or systematic sampling methods
• Cluster sampling


  1. Sampling at higher levels first before going down to lower levels

  2. Randomly take samples from provinces, then cities, municipalities, or barangays, then households
• Multi-stage sampling


  1. Combination of different sampling techniques

  2. Lottery method for regions and cities, then stratified sampling for chosen areas and clusters
• Non-random sampling


  Sample is not a proportion of the population and there is no system for selecting a sample
• Types of non-random sampling techniques


  • Accidental sampling
  • Quota sampling
  • Convenience sampling
  • Purposive sampling
• Accidental sampling includes only those whom the researcher meets by chance
• Quota sampling includes a specified number of persons of certain types to be taken as samples
• Convenience sampling is the most convenient and fastest sampling technique that makes use of the telephone, mobile phones, or the internet
• Purposive sampling is used in very small sample sizes, e.g. deans of certain universities or area managers of certain institutions