Psych 256 Exam 3

Bivariate correlations

Explain that measured variables, not any particular statistic, make a study correlational

Interrogate the construct validity and statistical validity (and, of lower priority, external validity) of an association claim

Explain why a correlational study can support an association claim, but not a causal claim

Multivariate correlations

Explain how longitudinal correlational designs can establish temporal precedence

Explain how multiple-regression analyses help address internal validity

Explain the function of a mediating variable

Simple experiments

Apply the three criteria for establishing causation to experiments, and explain why experiments can support causal claims

Identify an experiment’s independent, dependent, and control variables

Classify experiments as independent-groups and within-group designs, and explain why researchers might conduct each type of study

Evaluate three potential threats to internal validity in an experiment—design confounds, selection effects, and order effects—and explain how experimenters usually avoid them

Interrogate an experimental design using the four validities

Confounding variables

Interrogate a study and decide whether it rules out twelve potential threats to internal validity

Describe how researchers can design studies to prevent internal validity threats

Sampling

Explain why external validity is often essential for frequency claims

Describe which sampling techniques allow generalizing from a sample to a population of interest, and which ones do not

Population

entire set of people or things in which you are interested

Sample

smaller set of people or things taken from your population

Census

sample every member of the population

What is the population interest

population in not every person on the planet, but those to whom you hope your study generalizes

Biased sample

not all members of a population have an equal probability of being included

Representative sample

all members of a population have an equal probability of being included

When is a sample biased?

• convenient samples — sampling only those who are easy to contact (Amazon surveys - don’t have to recruit people)

• self selection bias — sampling only those who volunteer

Probability sampling techniques (obtaining a representative sample)

1. simple random sampling

2. systematic sampling

3. cluster sampling

4. multistage sampling

5. stratified random sampling

Simple random sampling

sample is chosen at random from the population of interest (names out of a hat)

Systematic sampling

use a randomly chosen number and count of every member of a population using that number (dice roll)

Cluster sampling

when clusters of participants within a population are randomly selected and then all individuals in each cluster are used (schools)

Multistage sampling

2 random samples, 1 is random sample of clusters, 2 is random sample of individuals within the clusters (not studying every preschooler but randomly selecting 10 from each school)

Stratified random sampling

multistage technique in which the researcher selects specific demographic categories and then randomly selects individuals from each category (gender, ethnicity)

• predetermine categories

• demographic categories then selecting within them

Oversampling

over represent one or more groups

Random assignment

2 or more groups where participants are randomly assigned (internal validity)

Random sampling

every person in the population has equal chance of being selected (external validity)

Non probability sampling techniques

1. convenient sampling

2. purposive sampling

3. snowball sampling

4. quota sampling

Convenient sampling

samples that are easy to access (undergrad students)

Purposive sampling

when you want to study certain kinds of people so you only recruit those kinds of people (convenience sample only targeting one group)

• standing outside of a smoke shop to recruit smokers

Snowball sampling

variation of purposive sampling, participants are asked to recommend other participants (illegal activities, embarrassing, sensitive)

Interrogating external validity

• in a frequency claim, external validity is a priority

• sampling technique, not a sample size, determines external validity

• frequency claim needs a representative sample