Evaluative research exam 1 Flashcards
what are the features of Random Assignment
People assigned to conditions based on chance.
Each person has a nonzero probability of being assigned to any given condition.
Random sampling is a different thing
What does Random assignment do for your study
Evenly distributes participant characteristics across conditions.
Rules out selection threat.
Makes it unlikely that other threats to internal validity are confounded with condition.
Basic random assignment design
subjects randomly assigned to treatment (Could be more than one) or control condition(or other treatment condition).
Post-test measure of outcome
Potential problem with random assignment
Attrition-people dropping out
Feasibility in terms of ethics and time or availibility of people that meet the criteria
it is difficult to randomize correctly
participants receive assigned treatment and no other
Why is attrition a problem in a random assignment design?
The people who drop out could be different in important ways (for particular conditions or the study as a whole) and their leaving could threaten validity.
Pretest helps assess the extent of the problem
Pretest-posttest design
Same as basic random assignment with a pretest condition, which could be used as a covariate or a repeated measures ANOVA can be performed.
Factorial design
Comnine two or more independent variables (factors) that each have at least two levels.
Major advantage: Test interactions along with main effects
Longitudinal design
Multiple pretest and posttest measurements of coutcome variable.
Show changes over time
Problems with longitudinal design
attriction, and can be unethical to withhold treatment for long periods of time
Crossover design
Two groups (randomly assigned), two treatment levels, put each group through both treatment conditions at different times: R O Xa O Xb O and R O Xb O Xa O
list the different Random assignment designs
Basic, Pretest-posttest, Factorial, Longitudinal, crossover
When would you use random assignment in feild research
when demand is greater than supply
when a treatment can’t be delivered to everyone at once
when temporal isolation is possible
when people are spatially seperated or don’t communicate much
when change is needed but it’s unclear which solution will work best
When there is ambiguous need
when some people have no preference among alternatives
when you can create your own organization
when you have control over experimental units
when loteries are expected
When should you not use random design
Short on time
research question is not about causation
impossible or unethical to manipulate the IV
More conceptual or empirical work must be done to determine whether an experiment is a good use of resources
What are some techniques of randomization
Simple random assignment
Restricted random assignment to force equal cell sizes
restricted random assignment to force unequal cell sizes
Haphazard assignment
Regression discontinuity design
subjects assigned to condition on the basis of a cutoff score on assignment variable
assignment variable mus be continuous and taken before the treatment
post-test measure after treatment
Interrupted time series
Building on the pre-test post test design by increasing number of both
the interuption is the treatment
time series because pretest and posttest measurements are taken at intervals
100 is a generally acceptable number of data points
interupted time series designs are vulnerable to what threats of validity?
History (biggest)-to alleviate make measurements intervals smaller.
Instrumentation
attrition
ITS additions to increase validity
Nonequivalent control group Nonequivalent DV Introducing and then removing treatment Multiple replications Switching replications
ITS potential difficulties
Gradual interventions
Delayed causation
Short time series
limitations of archival data
Quasi-experiments
attempt to test causal hypothesis
called “quasi” because they lack random assignment
How do you determine causation in quasi-experiments?
Cause precedes effect
cause co-varies with effect
Alternative explanations are implausible
Validity
The approximate truth of an inference
A matter of degree
A property of inferences, not designs or methods
Four types of validity
Statistical conclusion
Internal
Construct
External
Statistical Conclusion Validity
Validity of inferences about the covariance between treatment and outcome
I.E. How large and how reliable is the co-variation between the presumed cause and effect?