Lecture 4 - Experimental Design II Flashcards
What are the different kinds of validity?
- Internal validity
- External validity
- Statistical conclusion validity
- Construct validity
What is internal validity?
To what extent does the research tell us what we think it tells us
What are history effects (internal validity)?
An event (other than the manipulation) occurs between pretest and post-test and affects the study outcome
What are maturation effects (internal validity)?
Participants naturally change between pre-test and post-test
What is regression to the mean (internal validity)?
DV scores may vary up and down naturally over time and between individuals and groups.
What is testing effect (internal validity)?
Participants perform better at a post-test because they had practice
What is intrumentation effect (internal validity)?
Performance at pre- and post-test differs because different measures are used
What are selection effects (internal validity)?
Happens when random assignment fails (participants in different conditions are not equivalent)
What factor does mortality play in internal validity?
- Participants with certain characteristics drop out of the study (non-randomly)
- Probably doesn’t involve the death of any Ps, but they may leave the study for other reasons.
What is external validity?
The extent to which results can be generalised beyond the context of the study
What is ecological validity?
The extent to which results are generalised to other environments
What is temporal validity?
The extent to which results can be generalised to other times/ occasions
Why is it important to generalise findings to other populations?
Samples must be representative on theoretically relevant dimensions
What is the problem with having student samples?
- A problem when the process is expected to operate differently in a student population (e.g., social influence)
- Not a problem if we study a process that operates in the same way in all humans (e.g., perception)
What is gender bias?
Generalising from male Ps to people in general, e.g., Kohlberg’s moral development scale or research/advice around cardiac arrest
What is cultural bias?
Generalising to Ps from other cultures or backgrounds
What is statistical conclusion validity?
Is reduced when inappropriate statistical procedures are used
→ E.g. Assumptions made by a statistical test are not met by the data, such as normal distribution, scale type
What is construct validity?
- Adequate manipulations of IVs used
- Appropriate measures of DVs chosen
- In other words, operational definitions of IVs and DVs fit the purpose of the study
→ Allows researcher to test the effect of IV on DV
What is a between participant design?
–When the IV is an individual differences variable (i.e., self-selecting)
–When experience gained from participating in one condition makes it impossible to participate in another (e.g., deception)
What are the advantages of between participant designs?
Each participant is fresh and naive to the hypothesis
What are the disadvantages of between participant designs?
- More participants are needed to be recruited
- There may be unexpected differences between groups of participants
What is random assignment?
- Every participant has same chance of being placed in any of the conditions
- Objective is to spread important individual differences evenly across conditions, thus controlling for possible extraneous variables
- Select Ps and randomly allocate to group
- Goal is to spread important characteristics across groups
What are the possible issues with random assignment?
- Groups may not be equal size
- Random assignment doesn’t necessarily achieve even spread of important characteristics across conditions or groups
- Confounding variable?
What are three ways to create equal-sized groups?
- Block randomisation
- Stratified block randomisation
- Matching procedure, followed by random assignment