Task 8/Lecture 6 Flashcards
Error Variance
variability among scores caused by variables other than your independent variables.
Sources:
- rarely possible to hold all extraneous variables constant
- subjects differ in many ways
- environmental conditions
Reducing Error Variance
- Lab environment to ensure strict control
- using subjects with similar characteristics (reduces external validity)
- increasing the effectiveness of the independent variable
- random assignment - then use inferential stat to assess the probability with which error variance alone would produce between-group differences
Sources of carryover effects
Learning: subject may learn how to perform a task.
Fatigue: subject may become fatigued due to performance in earlier treatments
Habituation: reduction in responsiveness to a stimulus after repeated exposure.
Sensitization: exposure to a stimulus can cause subjects to respond more strongly to another stimulus.
Contrast: a contrast effect may emerge when subjects can compare what they receive in one condition to what they receive in another condition.
Adaptation: a subject can go through a period of adaptation. Adaptive changes may increase or decrease responsiveness to a stimulus.
Counterbalacing
assign the various treatments of the experiment in a different order for different subjects → distribute any carryover effects equally across treatments, so it does not produce differences in treatment that could be mistaken for the independent variable.
Complete counterbalancing: every possible order of treatments is tested
- only practical for experiments with small number of treatments
Partial counterbalancing: only some possible treatment orders –> these are chosen randomly.
Latin square design
the number of selected treatment orders equal to the number of treatments → each treatment is represented once in a row and once in a column.
(Partial counterbalancing)
Minimizing carryover effects
- Pre-train subjects
- Allow time for subjects to adapt/habituate.
- Allow breaks between treatments.
