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Flashcards in Experimental design Deck (35)
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What method is the best for identifying causal relationship?

- experimental method
- where groups systematically differ by only one variable


What internal validity threats are there to an experimenter's results?

1. Time
2. Group threats
3. Participant reactivity threats


What are more specific time related internal validity threats?

- history
- maturation
- Selection-maturation interaction
- repeated-testing
- instrument change


What are more specific Group related internal validity threats?

- selection: initial non-equivalence of groups
- regression to the mean
- Differential mortality
- Control group awareness of its status


What are more specific participant reactivity related internal validity threats?

- experimenter effects
- reactivity
- evaluation apprehension


Explain how history can threaten internal validity

- Extraneous events between pre-test and post-test affect ppt post test performance
SO add control


What in internal validity?

Having confidence that the changes to the dependent variable IS DUE to the independent variable


Explain how maturation threatens internal validity

- longitudinal experiment
- ppt can change during the course of the study
- so difference due to natural development/ things happening
SO have a control at each developmental point + try and control the natural programs


Explain how selection-maturation interaction threatens internal validity

- groups of different ages
- might have different maturation rates = response to manipulation
SO make sure they only differ by only one variable (eg match age)


Explain how repeated testing can threaten internal validity

- pre-test may improve their performance?
SO avoid repeated testing/ add control group who only get post-test


Explain how instrument change can threaten internal validity

Experimenter getting bored, not good = another systematic difference between conditions
SO having highly standardised procedures, random allocation + lots of familiarisation for the experimenter


Explain how initial non-equivalence of groups can threaten the internal validity

Cohort effect: groups differ on many variables other than the one interest


Explain how regression to the mean can threaten the internal validity

- testing once can result in extreme score and picking people from this score, their scores can be vastly different next time
SO select people randomly


Explain how differential mortality can threaten internal validity

- motivation to recover from something = making the treatment more effective


Explain how experimenter effects can threaten internal validity

- experimenters have expectations which may affect performance
- pygmalion effect
- Placebo effect
SO "double-blind" procedures if possible


What is the pygmalion effect?

Teacher's expectations affecting a pupil's IQ


Explain how reactivity can threaten the internal validity

Hawthorne effect
- productivity affected by other factors; Draper, 2006


What is the Hawthorne effect?

ppt's response may have been affected by their awareness of being studied/ experimental manipulatoins


What alternative reasons did Draper in 2006 give for why productivity may be affected in an experiment?

- Material factors
- Motivation - rewards?
- Learning - practice?
- feedback on performance
- Attention and expectations of observers


What are the different types of experimental design?

1. Quasi-experiemental designs
- no control over allocation of subjects to groups or timing manipulation of IV
2. True experimental designs


What are the different quasi-experimental designs?

1. One group pre-test/ post-test design
2. One-group post-test design
3. Interrupted time-series design
4. Static group comparison design


Describe the One-group post-test design

- after an event
EG: 9/11 lvls of anxiety
- prone to time effects
- no baseline against which to measure effects - pretty useless


Describe the one-group pre-test/ post-test design

- does have a baseline against which to measure effects of treatment (so like a control)
- still prone to time effects


Describe the interrupted time-series design

measurements are taken several times before and after the treatment
- still prone to time effects


Describe Static group comparison design

2 already pre-existing groups and compare them
- subjects are not allocated randomly to groups - so differences may be due to pre-existing group differences


What are the different true experimental designs?

1. Post-test only/ control group design
2. Pre-test/ post-test control group design
3. Solomon four group design


Describe the post-test only/ control group design

- RANDOM allocation
--> ensure observed differences are not due to pre-existing groups but can't be certain
- 2 different groups
- 1 = control


Describe the pre-test/post-test control group design

- RANDOM allocation
- measurement in the groups
- treatment
- measurement
--> ensures groups are indeed comparable before the experimental manipulation was administrated


Describe the Solomon four group design

- RANDOM allocation
- 4 groups
- A + B = pretest
- C + D = no pretest
- then either treatment or no treatment
- then measurement
--> ensures groups comparable before experimental manipulation
--> an pre-test hasn't affected performance
--> rarely used since need lots of people


What is the different between Within-subjects (repeated measures) and between-groups (independent measure) designs?

Between-groups (independent measures)
--> each subject in one condition only
Within-subjects (repeated measures)
--> Each subject does all of the conditions in a study