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PSY 311 Ch.8
Book notes and slides
| Question | Answer |
|---|---|
| 2 basic research designs are used to obtain the groups of scores that are compared in an experiment: | Within-subjects and between-subjects design |
| Within -subject design | the different groups of scores all can be obtained from the same group of participants |
| Between-subjects design | obtain each scores from a different group of participants, using a separate, independent group of individuals for each treatment condition being compared -allows only 1 score for each participant |
| Advantages of Between-Subjects experimental design | each individual score is independent from the other scores |
| Between-Subjects Design: each participant is exposed to only 1 treatment condition. Thus, the participant's score is not influenced by such factors as: | -practice or experiencing gain in other treatments -fatigue or boredom from participating in multiple treatments -contrast effects that results from comparing one treatment to another |
| Disadvantage of Between-subjects experimental design | require a relatively large number of participants -each score is obtained from a unique individual who has personal characteristics that are different from all the other participants -Individual Differences |
| Individual differences | are personal characteristics that differ from one participant to another -2 major concerns: can become confounding variables and produce high variability making it difficult to determine whether the treatment has any effect |
| 2 major sources of confounding that exist in a between-subjects design: | 1. confounding from individual differences 2. confounding from environmental variables |
| 3 general techniques for controlling confounding variables: | randomization, matching, and holding constant |
| With a between-subjects design, a researcher must also protect the study from individual differences between groups to make them equal. Specifically, the separate groups must be: | 1. Created equally 2. Treated equally 3. Composed of equivalent individuals |
| In a between-subject design, if the participants in one group have characteristics that are different from the participants in another group, then which of the following is threatened? | Internal validity |
| In a restricted random assignment, the group assignment process is limited to ensure | predetermined characteristics (such as equal size) for the separate groups |
| Advantage of using a random process: | fair and unbiased but does not guarantee a perfectly balanced outcome |
| Matching | the assignment of individuals to groups so that a specific variable is balanced or matched across the groups |
| Matching requires 3 steps: | 1. identification of the variable to be matched across groups 2. measurement of the matching variable for each participant 3. assignment of participants to groups by means of a restricted random assignment that ensures a balanced between groups |
| Holding variable constant | eliminate a variable, whenever a variable is prevented from reaching its natural range of variation, the external validity of the research is limited |
| Which of the following does not guarantee that a specific participant variable will not become a confounding variable? | randomizing the variable across treatment |
| Which of the following is a limitation of using matching rather than random assignment to form groups in a between-subjects experiment? | matching requires another measurement procedure |
| How does holding a variable constant prevent the variable from becoming a confound? | it eliminates the possibility that the variable will be substantially different from one group to another |
| Variance | a measure of validity obtained by computing the average squared distance from the mean |
| Big differences within treatments are bad because | the differences that exist inside the treatment conditions determine the variance of the scores |
| Variance within treatments | a measure of the differences between scores for a group of individuals who have all received the same treatment. Intent is to measure naturally occurring differences that have not been caused by a treatment effect |
| Minimizing variance within treatments | standardize procedures and treatment setting, limit individual differences, random assignment and matching, large sample size |
| Which of the following is an option for limiting the variance within treatment conditions? | hold a participant variable constant |
| Which of the following is a potential problem with holding a participant variable constant? | it threatens the external validity of the study |
| Attrition | refers to participants withdrawal from a research study before it is completed |
| Differential attrition | refers to differences in attrition rates from one group to another and can threaten the internal validity of a between-subjects experiment |
| Diffusion | a threat to internal validity that occurs when a treatment effect spreads from the treatment group to the control group, usually from participants talking to each other |
| Compensatory Equalization | a threat to internal validity that occurs when an untreated group demands to receive a treatment that is the same as or equivalent to the treatment received by another group in the research study |
| Compensatory Rivalry | a threat to internal validity that occurs when an untreated group learns about special treatment received by another group, then works extra hard to show they can perform just as well as that group |
| Resentful Demoralization | a threat to internal validity that occurs when an untreated group learns of special treatment given to another group, and becomes less motivated and productive because they resent the other group's expected superiority |
| The simplest version of a between-subjects experimental design involves comparing only 2 groups of participants: | the researcher manipulates 1 IV with only 2 levels (single-factor, 2 group design) -mean is computed for each group and then an independent-measures t-test |
| Advantage of two-group design | simplicity, best opportunity to maximize the difference between the 2 treatment conditions |
| Disadvantage of two-group design | provides little info., obtains only 2 real data points for comparison, limits the options when a researcher wishes to compare a treatment and control group |
| Single-factor multiple-group design | a research design comparing more than 2 groups of participants representing more than 2 levels of the same factor, conduct a single-factor ANOVA -mean computed for each group and single-factor analysis of variance is used to determine a diff. (post hoc) |
| Advantage of single-factor multiple-group design | tends to reduce or minimize difference between treatment |
| Disadvantage of single-factor multiple-group design | risk of reducing the differences between treatment so much that the differences are no longer significant |
| Experiments | experiments manipulate, not measure, the IV -Then measure and compare groups on the DV |
| Experiments rule out alternative explanations that can plague non-experimental studies | -directionality problem -confounding variables |
| Random assignment | experiments use RA- randomly assign people to a condition -groups should be similar before the manipulation -Quasi-experimental designs don't use random assignment |
| Manipulation: most basic experiment involves 2 groups: | -IV is manipulated in the experimental group -Not manipulated in the control group -Everything other than the manipulation should be the same |
| Posttest-only design | random assignment to a condition, manipulate the IV, measure the DV (post-test) |
| Advantages of posttest-only design | random assignment increase confidence that IV causes DV |
| Disadvantages of posttest-only design | cannot assess whether groups are actually similar pre-manipulation: even with RA, the groups might not be equal -cannot assess amount of change: unable to tell which (or both) conditions changed |
| Pretest-posttest design | Measure the DV (pre-test), random assignment to a condition, manipulate the IV, measure the DV again (post-test) |
| Advantages of pretest-posttest design | can assess equivalency of groups: pre-test can confirm whether groups are similar -can measure the exact amount of change |
| Disadvantages of pretest-posttest design | more time consuming, might inform participants of the hypotheses, pre-test might be a demand characteristic |
| Within subject design | participants are in all conditions -compare differences within subjects Ex: Robber's cave study: record behavior--> stage 1 ---> record behavior--> stage 2 |
| Advantages of a within-subjects design | eliminates preexisting differences between conditions -with within-subjects, such differences aren't possible because the same people are in all conditions |
| Disadvantages of a within-subjects design | Testing effects: participants could improve because of practice, not IV -Fatigue effects: participants could get worse because they are tired or bored, not IV -Sequence effects: outcome in one condition is influenced by previous condition |
| Between-subject design | participants are in only one condition -compare differences between subjects -we hope random assignment eliminates differences between groups |
| Addressing these issues in within-subjects design | Counterbalance conditions: some people get condition 1-->2, others get 2-->1, can identify sequence, testing, fatigue effects |
| Experiments can also be more complicated... -Ex: 2 experimental groups | Might want to compare experimental groups -more than 2 groups -more than 1 IV |
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