True experimental designs
experimental control: keeping all extraneous variables constant
randomization: making sure the experimental and control groups are equal at the start of the experiment
Basic Experiments
- manipulate the independent variable at at least 2 levels (experimental group and control group)
measure effect on dependent variable
Post Test- only design
Recruit participants randomly, assign to experimental and control groups. Manipulate IU, measure effect on DU for each group
- any difference should be due to the IU
- random assignment eliminates selection difference many personal characteristics
Pretest- PostTest Design
- same as pretest only design but includes a pretest- before the IV manipulation
- ensures that the groups were in foot equivalent at the start
Pros of Pretests
Pretest- is a good idea with small sample sizes
- pretest- enables us to see change after IV, including for individual participants
- especially important for some participants drop out after the start of the experiment (called attraction or mortality)
Pros of Pretests
pretest- is good with small sample tests
pretest- enables to see change after IV, including for individual participants
- especially important if some participants drop out after the start of the experiment (called attraction or mortality)
cons of the pretests
- In real world usually no pretest- so having one may reduce external validty
- may be time consuming
- may give away the topic of your experiment
Assigning participants to experimental conditions
- 2 basic options
- random assignment
- called an independent groups design or between- subjects design
- Use same group of participants in both/all conditions
- called a repeated measures design or within subjects design
Characteristics of Repeated Measures Design
- each participant is their own control/comparison
- need fewer participants since you get to use them twice
- easier to find statistically sificant differences because can compare each person to him/herself
- need to watch out for order effects where the previous condition affects the next one
0 deal with this prob either by delaying between conditions or by counterbalancing the order in which conditions are presented
Order effects
- Practice effect: someone might perform better on the second condition because of experience on the first
- Fatigue effect: someone might do worse on the second condition because they’re tired from the first
- carryover effect: the intervention from the first condition might still be affecting someone when they do the second
Complete Counterbalancing
all possible orders for conditions
- Latin square: a limited set of order that ensures that 1) each condition goes first, and last, and all the other positions, the same number of times, and 2) each condition precedes and follows each other conditionce
Matched Pairs Design
- instead of randomly assigning participants to groups, match them into pairs a relevant variable, and randomly assign one person in each pair to experimental or control group
- helps ensure the groups one equivalent, at least on the match variable
- most important with a small sample
Solomon four group design
Half participants recieve pretest and post test other half recieve only post test
- if there is no impact of pretest, the PostTest scores will be the same in the two control groups and expieremental groups
Post test only design
A true experimental design in which the dependent variable (PostTest) is m/ only once. after manipulation of the iv
Pretest- PostTest design
A true experimental design in which the dependent variable is measured both before (pretest) and after (PostTest) manipulation of the iv)
Solomon Four Group design
experimental design in which the experimental and control groups are studied with a ND without a pretest
Between Subjects Design
An experiment in which different subjects are assigned to each group. Also called independent groups design
Within Subjects Design
An experiment in which the same subjects are assigned to each group
Matched Pairs design
A method of assigning subjects to groups in which pairs of subjects are first matched on some Characteristic and then individually assigned randomly to groups
Mixed design
A mixed subjects design, also known as a mixed design, is a research design that combines elements of both a within-subjects design and a between-subjects design.
Between subjects design
A between-subjects experimental design is a type of design where participants are split into two or more groups and each group is assigned a treatment condition. These treatments are then compared to the other groups to see differences in the outcome of the experiment.
within subjects design
A within-subjects design is a research method that involves testing the same group of participants under multiple conditions or over time. It’s also known as a repeated measures design or dependent groups design.
dependent groups design
A “dependent groups design,” also known as a “within-subjects design” or “repeated measures design,” is a research design where every participant experiences all conditions of the independent variable
repeated measures design
A repeated measures design is a research method that involves measuring the same variable on the same subjects multiple times.
