Sampling Flashcards
What is sampling?
Process of selecting units from a population of interest to generalize results back to the population.
How to generate a sample?
5 steps:
Start with population of interest.
Find sampling frame.
Mirror the image of the population
Sampling techniques to draw sample.
Sampling bias.
What is the sampling frame?
A formal and exhaustive list of units or elements that constitute the population.
Must represent every possible unit in the population.
How do we ensure external validity based on sampling?
Sample must fairly represent the population. The effect size and direction of sample are similar to that of the population.
What is an element?
Basic unit that defines the study population (people or schools).
What is the goal of any sampling technique?
To maximize generalizability of the sample to the population.
What is sampling bias?
Difference between sample and population that is not attributed to chance.
Systematic difference in sampling such that some members of the intended population have a lower or higher sampling probability than others.
It results in a biased sample of a population in which all individuals, or instances, were not equally likely to have been selected.
What is extrapolation?
Process of using sample to make inferences about an entire population. Reducing sampling bias allows for extrapolation.
What is random selection?
Any sampling method that allows chance to operate in the selection of units from a sampling frame.
What is simple random selection?
Each element has an equal and non-zero chance of being selected.
What is systematic random sampling?
Select one random variable as starting point then each sample is selected at an interval.
Does not ensure equal and nonzero chance of selection.
What is an interval?
A pre-determined distance between elements in a sampling frame.
What is periodicity?
Inherent ordering of particular characteristic within sampling frame. Potential to enhance representativeness of sample.
There is a pattern in the population consistent with the value of k that is chosen in systematic sampling.
What is stratified random sampling?
Identification of some variable that may be related indirectly to the research question and this variable is used to divide population into strata.
Then random or systematic sampling.
Proportionate:
Represents overall population and key subgroups.
Disproportionate:
Uses different sampling fractions to over-sample a small group.
What does stratified random sampling allow for?
Ensures critical confounding variable is mirrored perfectly between sample and population.
Sample bias for at least one variable is reduced to 0.
What is cluster sampling?
Researchers divide a population into smaller groups of clusters. The sampling frame is made up of these clusters. A simple random sample is then obtained.
The cluster is the intended unit of analysis.
Good for policy or organizational BH studies.
What is multistage cluster sampling?
Combines cluster with simple random.
Select random clusters (primary sampling unit).
Then employ simple random sampling from each cluster (secondary sampling unit).
What is multistage cluster sampling prone to?
Design effect:
When sampling elements are inherently correlated with one another.
Fixed with large number of clusters; they tend to be homogenous which reduces sampling error.
What is stratified multistage cluster sampling?
Clusters may be divided into strata before random selection occurs.
Reduces sampling error to 0 for variables that may otherwise introduce sampling bias.
List types of probability sampling.
6:
Simple random. Systematic random. Stratified random. Cluster. Multistage cluster. Stratified multistage cluster.
What is probability sampling?
Probability sampling is defined as a sampling technique in which the researcher chooses samples from a larger population using a method based on the theory of probability. For a participant to be considered as a probability sample, he/she must be selected using a random selection.
What is convenience sampling?
Use pre-existing groups to facilitate recruitment of sample. People in group my be approached and asked to volunteer.
High risk of sampling bias (no procedure for representativeness).
May be differences between preexisting group and population.
What is venue-based-time sampling? VDT?
Two-stage sampling that allows researcher to generate a sample with known properties from hard to reach populations.
Improves upon convenience sampling as it interjects a systematic approach to make inferences about the venue-visiting population.
What is purposive sampling?
Also known as judgmental, selective, or subjective sampling, is a form of non-probability sampling in which researchers rely on their own judgment when choosing members of the population to participate in their surveys based on the purpose of their research.
