Chapter 11 (Within Subjects Experimental Design)

What statistic is used for a "two-related samples" within subjects design?

- related-samples t test

State and describe the two types of "controlling order":

-Complete counterbalancing= all possible order sequences in which participants receive different treatments are balanced or offset -Partial counterbalancing= some, but not all, possible order sequences in which participants receive different treatments or participate in different groups are balanced or offset in an experiment

Define within-subjects experimental design:

-Design in which the same participants are observed one time in each group of a research study 1) with two or more groups/assessments, observations for each participant occurs two or more times 2) reasons: to observe changes over time, to limit sample size

T of F: The between subjects design has greater power to detect an effect that the within subjects design? Why?

-False -We can remove the between-person's variance

A Solomon four-group design is an experimental design that includes four groups. Describe the procedures for each group.

-Group 1: pretest, treatment, post-test -Group 2: treatment, posttest -Group 3: pretest, posttest -Group 4: posttest

What is the relationship between the design and the within-subjects factor? What kind of threats are involved with this?

-The levels of a within-subjects factor are manipulated, then the same participants are observed in each group or at each level of the factor -Because groups and assessments occur at different times, other things that covary with time can influence the dependent variable (i.e., threaten internal validity) 1) maturation, testing, regression toward the mean, attrition 2) participant fatigue (esp. in intensive studies)

What is a within-subjects factor:

-Type of factor in which the same participants are observed in each group, or at each level of the factor 1) in non-experimental, longitudinal studies, the assessment points are the levels of the factor 2) in experimental studies, assessment points include different exposures

What is a matched-samples design?

-a within-subjects design in which participants are matched, experimentally or naturally, based on preexisting traits

What is a related sample?

-also called a dependent sample -the same or matched participants are observed in each group

What are time-related factors that need to be controlled for?

-attrition -testing effects -regression towards the mean -participant fatigue

What source of variability is attributed to each of the following: -indiv. differences -the manipulation -participant responding within each group

-between-persons variability -between-groups variability -within-groups variability

What are two ways to control timing?

-control the interval between treatments or groups -control the total duration of an experiment

How do we control for these threats to internal validity?

-controlling order (counterbalancing or partial counterbalancing) -control timing

Explain why the within-subjects design has greater power to detect an effect than the between-subjects design?

-fewer participants are required (economizing) -it's because we calculate it: * between subjects= (diff. or variance between groups)/(within-groups + between persons error) * within-subjects= (diff. or variance between groups)/(within-groups error)

What must be done in order to make a within-measures design count as an experiment?

-manipulate levels of the factor and include a comparison/control group -make added efforts to control for order and time-related factors

To minimize risks related to participant fatigue, what precautions are taken?

-minimize duration needed to complete an experiment -allow for a reasonable time interval or rest period between treatment presentations

What are the two types of matching in a matched-samples design?

-naturally occurring matched pairs (participants are matched based on preexisting characteristics) -experimentally matched pairs (participants are matched based on scores on a dependent measure)

What are the steps used for a with-subjects experimental design?

-obtain a sample -create two or more groups by manipulating the variable -observe the same participants in each group -control for order and time-related factors -measure the same dependent variable in each group -use inferential statistics to compare differences between groups -make a decision

What statistic is used for a "multiple related samples" within subjects design?

-one-way within-subjects analysis of variance

What is a related-samples t test and how do you calculate it? What else is it called?

-paired-samples t test -used to test hypotheses concerning the diff. in interval or ratio scale data for two related samples in which the variance in one population in unknown -t=mean difference between groups/mean difference attributed to error

What is the difference between a repeated-measures design and a matched-samples design?

-repeated measures can be used in an experiment -quasi-experimental uses a quasi-experimental design and can't be used in an experiment

What is counterbalancing?

-some subjects within a group will get treatment A first and then treatment B, while other subjects will get treatment B first and then treatment A

What source of variation is equal to zero using a within-subjects design? How does the related-samples t test estimate the source of variation, thereby reducing its value to zero?

-the between-persons source of variation -it eliminates the between-persons variability by reducing the data to one column of different scores

What are the two ways to select two related samples?

-the same participants are observed in each group -participants are matched, experimentally or naturally, based on common traits

What are the two common reasons that researchers observe the same participants in each group are as follows:

-to manage sample size -to observe changes in behavior over time

When is partial counterbalancing appropriate? How do you ensure that the few counterbalanced order sequences are representative of all order sequences?

-when there is a large number of groups -each treatment or group appears equally often in each position -each treatment or group precedes and follows each treatment or group one time

How do you calculate all possible number of order sequences?

= k! (number of treatments groups) -Ex. k=4, k1= (4 x 3 x 2 x 1)= 24

What is a carryover effect?

A threat to internal validity in which participation in one group carries over or causes changes in performance in a second group.

What are order effects?

A threat to internal validity in which the order in which participants receive different treatments or participate in different groups causes changes in a dependent variable.

In a within-subjects design, why do we assume that the value of the between-persons variability is equal to zero?

Because we assume that indiv. differences are the same in each group (there is no difference)

What is participant fatigue?

The state of physical or psychological exhaustion resulting from intense research demands

What is between-persons variability?

a source of variance in a dependent measure that is caused by or associated with individual differences or differences in participant responses across all groups.

What is within-group variability?

a source of variance in a dependent measure that is caused by or associated with observing different participants within each group.

What is between-groups variability?

a source of variance in a dependent measure that is caused by or associated with the manipulation of the levels (or groups) of an independent variable.

Which source of variation is computed and removed from the denominator of the test statistic for the one-way within subjects ANOVA?

between-persons variability

Which type of design, the between-subjects or within-subjects design, allows for the random assignment of participants to groups?

between-subjects

What test statistic is used to compare differences in interval or ratio data between two or more groups to which the same participants were observed in each group?

one-way within-subjects ANOVA

For a within-subjects design, the same participants are observed in each group or at each level of an independent variable. Which requirement of an experiment (manip., random., or comparison/control) is not met using this design?

randomization

Which sampling design, repeated measures of matched samples, can include the manipulation of an independent variable and is therefore more appropriate for use in an experiment?

repeated measures

What else is a within-subjects design called?

repeated measures design

State two ways that researchers control for order effects:

researchers control order and control timing

When we observe the same participants in each group, do we assume that the individual differences are the same or different?

same

Which design can be used when the same participants are observed in more than two groups?

the repeated measures (not matched samples)

Why do researchers compute a post hoc test?

to determine which pairs of group means significantly differ

Which type of design, the between or within, is associated with a smaller value in error variance?

within-subjects