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Experimental Psychology
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Terms in this set (65)
Post-test
A true experimental design in which the dependent variable (posttest) is measured only once, after manipulation of the independent variable
Solomon's 4 group design
Half of the participants are given the pretest; the other half receives the posttest only.
Repeated measures
an experiment in which the same subjects are assigned to each group.
IV
The variable that is manipulated to observe its effect on the dependent variable; variable that is the cause
DV
he variable that is the subjects response to and dependent on the level of the manipulated independent variable; Variable it effects
confounding variable
a variable that varies along with the independent variable; confounding occurs when the effects of the independent variable and an uncontrolled variable are intertwined so you cannot determine which of the variable is responsible for the observed effect.
Control
An extension of the interrupted time series quasi-experimental design in which there is a comparison or control group
randomization
ensures that the extraneous variable is just as likely to affect one experimental group as it is to affect the other group; determined entirely by chance
order effects
the order of presenting the treatments affects the dependent variable.
counterbalancing
a method of controlling for order effects in a repeated measures design by either including all others of treatment presentation or randomly determining the order for each subject.
representative sample
A subset of a statistical population that accurately reflects the members of the entire population. A representative sample should be an unbiased indication of what the population is like
Sampling error
When you only have a sample and it does not represent the entire population
Biased samples
a bias in which a sample is collected in such a way that some members of the intended population are less likely to be included than others
Straightforward Manipulation
manipulate variables with instructions and stimulus presentations; stimuli's may be presented verbally, in written form, videotape, or a computer
Staged manipulations
stage events during the experiment in order to manipulate the independent variable successfully
Self-Report
used to measure attitudes, judgments about someone's personality characteristics, emotional states
Behavioral
direct observations of behaviors
Physiological
recordings of responses of the body (EEG (electroencephalogram, EMG, GSR)
Ceiling Effect
the independent variable appears to have no effect on the dependent measure only because participants quickly reach the maximum performance level.
Floor effects
task is too difficult that hardly anyone can perform well
Demand characteristics
cues that inform the subject how he or she is expected to behave.
Single- Blind
participant is unaware of whether a placebo or the actual drug is being administrated.
Double-blind studies
Neither the participant nor the experimenter knows whether the placebo or the actual treatment is being given
Manipulation checks
An attempt to directly measure whether the independent variable manipulation has the intended effect on the participants
Pilot studies
Trial run with a small number of participants
Linear Relationships
Positive: Relationship in which increases in the values of the first variable are accompanied by increases in the values of the second variable
Negative: relationship in which increases in the values of the first variable are accompanied by decreases in the values of the second variable
Curvilinear relationships
relationship in which changes in the values of the first variable are accompanied by both increases and decreases in the values of another variable
Factorial designs
Designs with more than one independent variable (or factor); design in which all levels of each independent variable are combined with all levels of the other independent variables; allows investigation of the separate main effects and interactions of two or more independent variables
Interpreting main effect
The direct effect of an independent variable on a dependent variable
Interaction effects
The effect of one independent variable depends on the particular level of the other variable.
Moderating variables
Influences the relationship between two variables and independent and a dependent variable; in factorial the effect is revealed as an interaction.
Single case designs
An experimental in which the effect of the independent variable is assessed using data from a single participant.
Reversal designs
a single case design in which the treatment is introduced after a baseline period and then withdrawn during a second base line period. It may be extended by adding a second introduction of the treatment. Sometimes called "withdrawal" design.
Multiple baseline designs
Effectiveness of the treatment is demonstrated when a behavior changes only after the manipulation is introduced.
Quasi-experimental designs
A type of design that approximates the control features of true experiments to infer that a given treatments did have its intended effect
Pretest-posttest designs
is that the latter pretest is given before the experimental manipulation is introduced
Non-equivalent control group designs
separate control group, but he participants in the two conditions- the experimental group and the control group are not equivalent
Regression toward the mean
occurs whenever participants are selected because they score extremely high or low on some variable.
Self-selection bias
Individuals select themselves into a group
Cross-sectional method
person of different ages are studied at only one point in time
longitudinal designs
the same group of people is observed at different points in time as they grow older.
Nominal Scale
categories; have no numerical, quantitative properties (Ex. Males and females)
Ordinal Scale
allow us to rank order the levels of the variable being studied
Interval Scale
intelligence, aptitude test; difference between the numbers on the scale is meaningful
Ratio Scale
have an absolute zero point that indicates the absence of the variable being measured ex. Weight, age, reaction time
correlation coefficients
Index of how strongly two variables are related to each other
Effect size
the extent to which two variables are associated. In experimental research the magnitude of the impact of the independent variable on the dependent variable
regression
Used to predict a person's score on one variable when that persons score on another variable is already known
Third variable problem
Any variable that is extraneous to the two variables being studied
Null hypotheses
population means are equal- the observed difference is due to random error.
Research hypotheses
The population means are not equal; independent variable did have an effect
One-tailed test
Specified a direction of difference between the groups
two-tailed tests
did not specify a predicted direction of difference
File drawer problem
many studies in a given area of research may be conducted but never reported, and those that are not reported may on average report different results from those that are reported.
What does "statistically significant" really mean
very low probability of occurring if the population means are equal.
T-test
Used to examine whether two groups are significantly different from each other.
F-test
(Analysis of variance)- Statistical significance test for determining whether two or more means are significantly different. F is the ratio of systematic variance to error variance
Type I Error
Made when we reject the null hypothesis but the null hypothesis is actually true.
Type II errors
When the null hypothesis is accepted although in the population the research hypothesis is true.
Internal validity
Ability to draw a conclusions about casual relationships from our data) certainty in which results of an experiment can be attributed to the manipulation of the independent variable rather than some other confounding variable
External validity
the extent/degree to which findings of an experiment may be generalized
Random sampling
choose your entire group of participants randomly from a given population of potential participants.
convenience samples
selecting subjects in a haphazard manner, usually on the basis of availability, and not with regard
Problems with using convenience samples
Introduce biases into the sample so that the sample may not be an accurate representation of the population
Volunteer bias
External validity of the findings may be limited because the data from volunteers may be different from what would be obtained with a more general sample
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