Week Four Flashcards
internal validity
how sound is the design, how strongly can we assert that changes in our DV are down to our IV and not other things we haven’t controlled for.
external validity
how generalizable are our findings, how representative of the real world is the study.
steps to internal validity
- Sound operationalisation of the DV
○ Measures should be reliable and valid.- Strong experimental design logic
- Sound operationalisation of our Ivs
- Consideration and use of appropriate remedies to control for extraneous variables.
factorial
more than one IV
○ May have all repeated measures or all between groups or mixed.
○ Allows examination of interplay between two or ore Ivs and the splitting p of these effects into interactions and main effects.
strengths of factorial designs
○ More than one independent variable allows for more precise hypotheses.
○ Control of extraneous variable by including as an independent variable.
Ability to determine the interactive effect of two or more independent variables
main effect
○ The influence of one independent variable on the dependent variable
One main effect for each IV in a study
interaction effect
○ The joint, combines or interactive effect of two or more independent variables on the dependent variable.
factorial design notation
2 x 3
= 2 IVs, one 2 levels and one 3 levels
weakness of factorial design
- Using more than 2 IVs may be logistically cumbersome.
- Higher order interactions are difficult to interpret.
variability
In any study, what we are trying to do is establish whether the variation in the DV between groups I different from the normal variation in the DV within groups.
how to ensure a strong experimental design
- In order to maximise our chances of getting a true picture of how the IV affects the DV we need to:
○ Maximise the impact on our dependent variable that is related to the independent variable.
§ Increase between group/condition/level variation.
○ Minimise variation in our dependent variable that is not related to our independent variable
§ Compress within group/condition variation.
Done by adopting good research design and controlling variables.
separation
In any experiment we are trying to establish whether the variation in the DV between groups (caused by the IV) is different from normal variation in the DV within groups.
Separation of the IV and DV: achieved by IV operationalisation
compressions
achieved by controlling extraneous variables.
types of extraneous variables
○ Noise creating
§ Randomly impact the DV, not related to the IV, but potentially create extra variation in the DV not due to the IV, want to minimise this.
§ Has an effect randomly on the DV
○ Confounding
§ Systematically impact the DV, related to the IV, potentially explaining changes in the DV that you would be expecting the IV to make, want to control for this by eliminating, keeping constant or building into study so can measure impact.
§ Varies systematically on the DV.
EVs and between groups
- Two separate groups of people who could differ on a whole range of things. Both relevant and irrelevant to the study at hand.
self assignment
Self assignment: subject selects which treatment groups
experimenter assignment
experimenter selects which treatment group.
arbitrary assignment
selection based on seemingly non-relevant criteria.
random assignment
- Random Assignment/Allocation: best to have no criteria for selection.
○ Provides max. insurance that the groups are equal.
○ Eliminates systematic differences between groups.
○ Doesn’t eliminate Evs but does help to decrease.
matching
○ Use of a variety of techniques to equate participants in the treatment groups on specific variables.
§ Should be done with variables thought to be related to the IV or may confound the IV
□ E.g. intelligence, age etc.
○ Advantages
§ Controls for the variables on which participants are matched
§ Increases the sensitivity of the experiment.