External validity
The extent to which we can generalize the results of a research study to people, settings, times, measures, and characteristics other than those used in that study.
Population
Set of all people, objects, or events of interest to the researcher
Population element
Single member of the population
Stratum
Mutually exclusive subsets of the population containing population elements that have a common characteristic
Sample
Group of population elements used in an experiment
Sampling error
difference in the distribution of characteristics between a sample and the population as a whole
Law of Large Numbers
The larger a sample, the more likely values obtained from the sample will be similar to the actual values of the population.
Types of Probability sampling
Simple Random Sampling
Stratified Random Sampling
Cluster Sampling
Types of Non-probability sampling
Convenience Sampling
Quota Sampling
Snowball Sampling
Probability sampling
Sampling method in which every element of the sampled population has a known probability of being included in the sample
Nonprobability sampling
sampling method in which there is no way to estimate the probability each element has of being included in the sample
Simple random sampling
sampling method in which all population elements have the same chance at being selected
Stratified random sampling
sampling method in which population is divided into homogenous subgroups and simple random samples are drawn from each subgroup
Cluster sampling
: sampling method in which a random sample of pre-existing clusters/groups are selected from a larger list of clusters within a population
Convenience sampling
sampling method in which the most easily/readily available individuals are selected
Quota Sampling
sampling method in which subgroups of interest are identified, then quotas are set for the number of individuals to be collected within each subgroup.
Snowball sampling
sampling method in which members of the initial sample from the target population enlist other members of the target population who meet the criterion for inclusion