Upload
buck-warren-oconnor
View
223
Download
3
Embed Size (px)
Citation preview
PSYC2030Exam Review #2
March 13th 2014
Chapter 5
Essential Features of Experimental Research
• What is an independent variable and what is meant by the term “levels” of an independent variable? Independent variable:
The factor of interest to the researcher Must have a minimum of two levels
(Situations/Conditions) Can be manipulated by the experimenter
E.g., experimentally eliciting anxiety in Group A but not in Group B
Participants can be selected based on their attributes E.g., selecting two groups that differ in
anxiety level
Essential Features of Experimental Research
• Distinguish between an experimental and a control group. Experimental group:
Receives treatment Control group:
Treatment is withheld = comparison group
Essential Features of Experimental Research
• What is a confounding variable and why is it a problem in experimental research? Confounding variable:
Any uncontrolled extraneous variable that covaries with the independent variable and could provide an alternative explanation of the results
Problem?Difficult to interpret resultsResults could be due to the effect of the
independent variable, confounding variable, or some combination of both
Essential Features of Experimental Research
• In psychological research, what is a dependent variable? Behaviour measured as an outcome of an
experiment If we study the effect of X on Y
X = Independent Variable Y = Dependent Variable
Essential Features of Experimental Research
• What is the difference between a ceiling and a floor effect? Ceiling effect
The average score in both groups is so high that no difference can be determined E.g., questions are too easy
Floor effect The average score in both groups is so low
that no difference can be determined E.g., questions are too difficult
Manipulated versus Subject Variables
• What is meant by a subject variable? Give two examples. Subject variable: Existing characteristics
of the individual participating in the study Examples
Sex Age Socioeconomic status
Manipulated versus Subject Variables
• When drawing conclusions from studies using manipulated variables, statements about cause can be made. These statements cannot be made when using subject variables. Why? With manipulated variables, groups are created based
on random assignment The researcher can be fairly confident that the groups
are are equal (i.e., any differences will be random) With subject variables, groups are created based on
participants’ characteristics The researcher can’t be certain that the groups are equal
(i.e., differences might not be random) Any differences might be due to individual differences
than covary with the subject variables
The Validity of Experimental Research
• Give two examples of mistakes that result in a loss of statistical conclusion validity. What is statistical conclusion validity?
The extent to which the researcher uses statistics properly and draws the appropriate conclusions from the statistical analysis
Examples of mistakes: Using the wrong analysis technique or violate
some of the assumptions required for performing a particular analysis
Reporting some results but not others
The Validity of Experimental Research
Distinguish internal from external validity. Internal validity: the degree to which an
experiment is methodologically sound and confound-free
External validity: the degree to which research findings generalize beyond the specific experiment being conducted
Threats to Internal Validity• How might attrition reduce an experiment’s internal
validity? Attrition: participants leaving the study over the
course of time Problem?
The group finishing the study is made up of different types of people than is the group that started the study.
Threats to Internal Validity• Distinguish between testing and instrumentation
as threats to the internal validity of a study. Testing: Occurs when the fact of taking a pretest
influences posttest scores (perhaps by sensitizing participants to the purpose of the study)
Instrumentation: Occurs when the measuring instrument changes from the pretest to the posttest
Chapter 6
Between-Subjects Designs In a between-subjects design, why is it
important to aim for equivalent groups? Between subjects design: an experimental
design in which different groups of participants serve in the different conditions of the study
we want to make sure that any differences between the groups is due to the levels of the independent variable
Between-Subjects Designs Other than the problem of equivalent groups,
what is a disadvantage of using a between-subjects design? Large numbers of people may be need to be
recruited, tested, and debriefed during the course of the study
The Problem of Creating Equivalent Groups
What is the difference between random selection and random assignment? Random selection: A procedure for getting
volunteers to come into your study. Every person has an equal chance to participating.
Random assignment: A procedure to assign participants to conditions. Every person participating has an equal chance of bring placed in any of the conditions/groups in the study.
The Problem of Creating Equivalent Groups
Explain how random assignment accomplishes the goal of creating equivalent groups Individual differences are randomly spread
out across conditions
The Problem of Creating Equivalent Groups
Explain how simple random assignment differs from blocked random assignment With simple random assignment, there is
no guarantee that the groups will be equal in size (e.g., flipping a coin 20 times can result in heads all 20 times)
With blocked random assignment, participants are assigned to blocks of alternating conditions
Within-Subjects Designs
What are the advantages of within-subjects designs over between-subjects designs? Within-subjects designs: an experimental
design in which the same participants serve in each of the conditions of the study
Advantage over between-subjects designs?Fewer people are required!Eliminate the equivalent groups problem
Within-Subjects Designs
What is the main problem that a within-subjects design has to solve? Order effect: the experience of
participating in one condition of the study influences performance in subsequent conditions
Within-Subjects Designs
What is the difference between a progressive effect and a carryover effect? Progressive effect: performance changes
steadily from trial to trial (e.g., fatigue) Carryover effect: performance changes as
a result of one sequence of events rather than another (e.g., easy-difficult Qs vs. difficult-easy Qs)
The Problem of Controlling Sequence Effects
• What is the general purpose of counterbalancing? The order of conditions/presentation is
randomized for each subject, thus eliminating order effects
The Problem of Controlling Sequence Effects
what is “complete” counterbalancing? If there are five different conditions in a study, how many sequences will be needed if complete counterbalancing is going to be used? complete counterbalancing occurs when
all possible orders are used Five conditions: 5! = 120 sequences
The Problem of Controlling Sequence Effects
• What is “partial” counterbalancing? What are two ways to accomplish partial counterbalancing? Partial counterbalancing: a subset of all
possible orders of conditions is used Sampling from the complete set of all
possible orders Randomizing the order of conditions for
each subject
Control Problems in Developmental Research
What is a cross-sectional design? In developmental psychology, a design in
which age is the independent variable and different groups of people are testedEach group is of different age
Control Problems in Developmental Research
What are cohort effects and how might they make the interpretation of cross-sectional designs difficult? Cohort: group of people born at the same
time Cohort effects: differences between
groups are due to growing up in different historical times
Control Problems in Developmental Research
What is a longitudinal design? In developmental psychology, a design in
which age is the independent variable and the same group of people is being tested repeatedly at different ages
Control Problems in Developmental Research
Describe how a cohort sequential design combines elements of cross-sectional and longitudinal designs A new cohort is added to a study every few
years and then studied periodically throughout the time course of the study
Attempts to balance cohort and attrition problems
Problems with Biasing What is experimenter bias and how can it be
demonstrated experimentally? Occurs when an experimenter’s
expectations about a study affect its outcome
Problems with Biasing What are two ways to control experimenter
bias? Research protocols: detailed descriptions
of of the sequence of events in a research sessionEnsures uniformity of treatment of research
participants A double blind procedure: neither the
participant nor the experimenter knows which condition of study is being tested
Problems with Biasing What is the Hawthorne effect?
A form of participant bias in which a participant’s behaviour is influenced by the mere knowledge of being in an experiment and therefore important to the experimenter
Problems with Biasing• What is the good subject effect, how does it relate
to demand characteristics, and how might it influence the outcome of a study? Good subject effect: A form of participant bias in
which participants try to guess the experimenter’s hypothesis and then behave in such a way to confirm it
Demand characteristics: A feature of the experimental design that increases the chance that participants will detect the true purpose of the study
Problems with Biasing• How can participant bias be controlled?
Reduce demand characteristics Deception Placebo control group
Manipulation check: Asks participants what they thought the
study was about Checks for the presence of demand
characteristics Conduct field research
Chapter 7
Single-Factor – Two Levels• Describe the Stroop effect and explain why his
first two studies were examples of single factor repeated-measures designs. Single factor design: An experimental
design with a single independent variable Stroop effect: When the name of a color is
printed in a color that doesn’t match the name, naming the color of the word takes longer and is more prone to errors than when the color of the ink matches the name of the color
Single-Factor – Two Levels Identify the situations when a t test for
independent samples will be used and when a t test for related samples will be used. Independent t-test
Used when two groups are completely independent from one another Random assignment Subject variables with two groups (males vs. females)
Dependent samples t-test: Matched groups design Repeated-measures designs
Presenting Data There are Three Ways: 1. Numbers can be presented in
sentence form 2. Construct a table of results 3. Graphical Representation
Presenting Data • How you present your data depends on the
type of IV you are interested in... Continuous Data: Use a line graph, but a
bar graph is adequate Discrete Data: Use a bar graph, line graph
is inappropriate. The IV is always presented on the X axis
or the horizontal line The DV is always presented on the Y axis
or vertical line
Control Group Designs• What is a placebo and what is the reason for
including a placebo control group in an experiment? Placebo: a substance given to a
participant in a form suggesting a specific pharmacological effect when in fact the substance in inactive
Purpose? Sometimes effect is caused simply by believing in the drug.
Control Group Designs Placebo Control Groups: Participants
are led to believe they are expecting some treatment when they are actually not. This type of control group is often used in pharmacological studies
Control Group Designs Waitlist Control Groups: Often used
to assess the effectiveness of the program and helps eliminate alternative explanations for the results you obtain such as general improvement because of passage of time
Control Group Designs Yoked Control Groups: when each
member of the control group is matched or “yoked” to a member of the experimental group so that the amount of time spent participating in the events in each condition is equivalent across your groups.