Week 7 - Sampling Flashcards
Define: population, sample and census
Population: the entire set of people or products in which you are interested
Sample: smaller set, taken from a population
Census: getting info from every item in a population
What is a bias sample?
Some people have a higher chance of getting included in the sample than others
How can biased samples happen? what are the terms used to describe these processes?
Convenience sampling - sampling only those who are easy to contact and readily available to participate
Self-selection - when a sample is known to contain only people who volunteer to participate
Define probability sampling? what are the different types of probability sampling?
Probability Sampling; every member of the population of interest has an equal and known chance of being selected for the sample (rando)
Simple rando samp
Cluster samp
Multistage samp
Stratified rando samp + oversampling
Define non probability sampling? what are the different types?
Nonprobability sampling; techniques involve nonrandom sampling and result in a biased sample
Purposive samp
Snowball samp
Quota samp
Define and give examples of simp rando samp and cluster samp?
Simp rando - pick random people
Ex: pingpong balls in a cup, completely equal chance of getting whoever
Cluster samp - people pre-divided into arbitrary groups, then random groups out of those groups are selected (all indis in each group are used)
Ex: make random groups of colors, randomly select groups of colors from those groups (use all colors from the random groups selected)
Define and give examples of multistage samp, stratified rando samp + oversampling
Multistage Sampling; two random samples; sample of clusters and sample of people within those clusters
Ex: choose random groups of candy, choose randoms candies from those groups
Stratified random Sampling; researcher purposefully selects particular demographic categories, and then randomly selects individuals in each of the categories
a) Strata are meaningful categories, clusters arbitrary.
b) Strata final sample size reflect their proportion in the population, clusters do not
Oversampling; (variation of stratified random samp.) Researcher intentionally over represents one or more groups.
Define systematic sampling?
Using computer or random number table, researcher pick 2 nums, ex) 4 & 7. Researcher would start at 4 and count by 7 until the sample is the desired size.
Define random assignment? what validity does this enhance?
what validity does random sampling enhance?
Rando assignment: (only in experimental designs) when researchers want two groups, assign them at random.
Random Sampling enhances EXTERNAL VALIDITY, Random Assignment enhances INTERNAL VALIDITY
Define purposive sampling? Give an example?
When, in a non random way, researchers want to study a specific group of ppl, recruiting only those ppl.
Ex: recruiting smokers by putting up posters at a local tobacco store
Define snowball sampling?
Participants are asked to recommend a few acquaintances for the study.
Unrepresentative and un-random
Define quota sampling?
Researcher identifies subsets of the population of interest and then sets a target number for each category in the sample
What is the no. 1 validity in a frequency claim?
External validity, ei generalization, in a priority
