PSYC 270 QUIZ 3

population

population

A larger group from which a sample is drawn; the group to which a study’s conclusions are intended to be applied.

Sample

The group of people, animals, or cases used in a study; a subset of the population of interest.

census

A set of observations that contains all members of the population of interest.

biased sample

A sample in which some members of the population of interest are systematically left out, and therefore the results cannot generalize to the population of interest.

Also called unrepresentative sample.

unbiased sample

A sample in which all members of the population of interest are equally likely to be included (usually through some random method), and therefore the results can generalize to the population of interest.

Also called representative sample.

convenience sample

Choosing a sample based on those who are easiest to access and readily available; a biased sampling technique.

self-selection

A form of sampling bias that occurs when a sample contains only people who volunteer to participate.

probability sampling

A category name for random sampling techniques, such as simple random sampling, stratified random sampling, and cluster sampling, in which a sample is drawn from a population of interest so each member has an equal and known chance of being included in the sample.

Also called random sampling.

nonprobability sampling

A category name for nonrandom sampling techniques, such as convenience, purposive, and quota sampling, that result in a biased sample.

simple random sample

The most basic form of probability sampling, in which the sample is chosen completely at random from the population of interest (e.g., drawing names out of a hat).

systematic sampling

A probability sampling technique in which the researcher uses a randomly chosen number N, and counts off every Nth member of a population to achieve a sample.

cluster sampling

A probability sampling technique in which clusters of participants within the population of interest are selected at random, followed by data collection from all individuals in each cluster.

multistage sampling

A probability sampling technique involving at least two stages: a random sample of clusters followed by a random sample of people within the selected clusters.

stratified random sampling

A form of probability sampling; a random sampling technique in which the researcher identifies particular demographic categories, or strata, and then randomly selects individuals within each category.

oversampling

A form of probability sampling; a variation of stratified random sampling in which the researcher intentionally overrepresents one or more groups

random assignment

The use of a random method (e.g., flipping a coin) to assign participants into different experimental groups.

purposive sampling

A biased sampling technique in which only certain kinds of people are included in a sample.

snowball sampling

A variation on purposive sampling, a biased sampling technique in which participants are asked to recommend acquaintances for the study.

quota sampling

A biased sampling technique in which a researcher identifies subsets of the population of interest, sets a target number for each category in the sample, and nonrandomly selects individuals within each category until the quotas are filled.

bivariate correlation

An association that involves exactly two variables.

mean

An arithmetic average; a measure of central tendency computed from the sum of all the scores in a set of data, divided by the total number of scores.

effect size

The magnitude, or strength, of a relationship between two or more variables.

replication

The process of conducting a study again to test whether the result is consistent.

outlier

A score that stands out as either much higher or much lower than most of the other scores in a sample.

restriction of range

In a bivariate correlation, the absence of a full range of possible scores on one of the variables, so the relationship from the sample underestimates the true correlation.

curvilinear association

An association between two variables which is not a straight line; instead, as one variable increases, the level of the other variable increases and then decreases (or vice versa).

directionality problem

In a correlational study, the occurrence of both variables being measured around the same time, making it unclear which variable in the association came first. See also temporal precedence.

third-variable problem

In a correlational study, the existence of a plausible alternative explanation for the association between two variables.

spurious association

A bivariate association that is attributable only to systematic mean differences on subgroups within the sample; the original association is not present within the subgroups.

moderator

A variable that, depending on its level, changes the relationship between two other variables.

statistically significant

In NHST, the conclusion assigned when when p < .05; that is, when it is unlikely the result came from the null-hypothesis population.