Quiz 1 - Sampling

what is random sampling?

• a sampling technique in which everyone in the population has an equal chance of being selected

what is the difference between internal and external validity?

• internal validity: the extent that a change in the DV can be attributed to the IV; the extent that a study can rule out alternate explanations for the relationship between two variables

• external validity: the extent that findings from a sample can be generalized to the corresponding population

• what are the different types of probability sampling methods?

  • (simp ran, syst, strat, prop strat, clus)

• simple random: everyone has an equal and independent chance of selection

  • independence: means that the choice of one individual does not influence or bias the probability of choosing another individual

• systematic: select every nth participant from a list containing the total population after a random starting point

• stratified: identify pre-existing groups, then draw random samples of equal size from groups (although the corresponding groups in the population may not necessarily be the same size)

  • ex. suppose the pre-existing groups are left and right handed people, and that 88% of people are right-handed

  • 50 right 50 left (not proportionate to percentage of people who are r and l in population)

• proportionate stratified: identify pre existing groups, then draw random samples of proportionate size groups

  • ex. 12 L and 88 R

• identify pre-existing clusters, randomly select some clusters, and then measure everyone in the selected clusters

  • ex. suppose the pre-existing clusters are 3rd grade classes in public school in CA. Assign each class a number, draw a random sample of these numbers, and then include all 3rd graders from those classes in the study

• what are the different types of nonprobability sampling methods?

  • convenience, quota, snowball

• convenience: recruit participants who are easily accessible

• quota: identify pre-existing subgroups, recruit a specific number of participants from each group (using a non-random selection method)

• snowball: ask participants to help recruit more participants by asking people they know to also participate

memorize this chart