5.6: Experimental Research (Summary)
- Page ID
- 309646
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)Key Takeaways
Key Terms and Concepts
EXPERIMENT
A study that manipulates an independent variable, measures a dependent variable, and controls extraneous variables.
INDEPENDENT VARIABLE
The variable that the researcher manipulates.
DEPENDENT VARIABLE
The outcome variable that is measured.
CONDITIONS
The different levels or values of the independent variable.
CONTROL
Holding extraneous variables constant or using random assignment.
EXTRANEOUS VARIABLES
Variables other than the IV that might affect the DV.
SINGLE FACTOR TWO-LEVEL DESIGN
An experiment with one independent variable with two levels.
SINGLE FACTOR MULTI LEVEL DESIGN
An experiment with one independent variable with three or more levels.
CONFOUNDING VARIABLE
An extraneous variable that varies systematically with the independent variable.
TREATMENT
An intervention or manipulation applied to participants.
TREATMENT CONDITION
A condition in which participants receive the experimental treatment.
CONTROL CONDITION
A condition used for comparison that does not receive the treatment.
RANDOMIZED CLINICAL TRIAL
An experiment testing a treatment with random assignment.
PLACEBO
An inactive substance or fake treatment given to control for expectation effects.
PLACEBO EFFECT
Improvement resulting from expectations rather than the treatment itself.
PLACEBO CONTROL CONDITION
Participants receive a placebo that resembles the treatment, but lacks the treatment element.
WAIT-LIST CONTROL CONDITION
Participants are told they will receive the treatment at a later time.
BETWEEN-SUBJECTS EXPERIMENT
An experiment where different participants are in each condition.
RANDOM ASSIGNMENT
Assigning participants to conditions using a random process.
BLOCK RANDOMIZATION
Random assignment in blocks to ensure equal sample sizes.
MATCHED-GROUPS DESIGN
Matching participants on key variables before randomly assigning them to conditions.
WITHIN-SUBJECTS EXPERIMENT
An experiment where the same participants experience all conditions.
ORDER EFFECT
The influence of experiencing one condition on performance in subsequent conditions.
CARRYOVER EFFECT
Effects from one condition that persist into the next condition.
PRACTICE EFFECT
Improvement in performance due to repeated practice or exposure.
FATIGUE EFFECT
Decline in performance due to tiredness or boredom.
CONTEXT EFFECT (OR CONTRAST EFFECT)
The influence of one condition on another by providing a comparison context.
COUNTERBALANCING
Varying the order of conditions across participants to control for order effects.
COMPLETE COUNTERBALANCING
Including all possible orders of conditions.
RANDOM COUNTERBALANCING
Randomly determining the order of conditions for each participant.
INTERNAL VALIDITY
The degree to which changes in the dependent variable are directly caused by the independent variable, and not other factors.
EXTERNAL VALIDITY
The degree to which findings generalize beyond the study.
MUNDANE REALISM
The extent to which an experimental situation resembles real-world situations.
PSYCHOLOGICAL REALISM
The extent to which an experiment creates genuine psychological involvement.
CONSTRUCT VALIDITY
The extent to which the test or measure adequately measures the constructs.
OPERATIONALIZATION
The process of defining constructs in measurable terms.
STATISTICAL VALIDITY
Whether statistical conclusions are appropriate and accurate.
SUBJECT POOL
A group of individuals available for participation.
EXPERIMENTER EXPECTANCY EFFECT
Researcher expectations that influence participant behavior or data interpretation.
DOUBLE-BLIND STUDY
A study where neither participants nor experimenters know who is in which condition.
MANIPULATION CHECK
A measure to verify that the independent variable manipulation had its intended effect.
PILOT TEST
A small-scale trial run to identify problems before conducting the full study.
Test Your Knowledge (answers at end of section)
1. What is the key characteristic that distinguishes an experiment from other research methods?
A. Experiments are conducted in laboratories
B. Experiments involve the manipulation of an independent variable by the researcher
C. Experiments use larger sample sizes than other methods
D. Experiments are more expensive than other research methods
2. A confounding variable differs from an extraneous variable in that a confounding variable:
A. Cannot be controlled by the experimenter
B. Varies systematically with the independent variable
C. Is always related to participant characteristics
D. Only occurs in between-subjects designs
3. Researchers studying a new therapy find that patients in the treatment condition improve more than those in a no-treatment control condition. However, they cannot conclude the therapy works because:
A. The sample size was too small
B. The improvement could be due to placebo effects rather than the therapy itself
C. Random assignment was not used
D. Internal validity was too high
4. In a between-subjects design, each participant experiences:
A. All levels of the independent variable
B. Only one level of the independent variable
C. Both the independent and dependent variables
D. Multiple dependent variables simultaneously
5. Complete counterbalancing becomes impractical when the number of conditions is large because:
A. Participants cannot remember which condition they were in
B. The number of possible orders increases factorially (e.g., 6 conditions = 720 orders)
C. Carryover effects become too strong
D. Random assignment no longer works effectively
6. A researcher finds that sleep deprivation reduces test performance in a laboratory study, but participants knew they were being studied and the artificial environment may have affected results. This scenario illustrates concerns about:
A. Statistical conclusion validity
B. Internal validity
C. External validity (generalizability)
D. Construct validity
7. Fredrickson and colleagues had participants complete a math test while wearing a swimsuit. Although this seems artificial, the researchers argued the study has value because:
A. It has high mundane realism since people often wear swimsuits
B. The psychological process of self-objectification likely operates in various situations, giving it psychological realism
C. Laboratory studies always have high external validity
D. Statistical validity is more important than external validity
8. When is it most appropriate for a researcher to use a manipulation check in an experiment?
A. Only in between-subjects designs
B. When the researcher wants to verify that the independent variable manipulation had its intended psychological effect on participants
C. Only when using random assignment
D. When the dependent variable is difficult to measure
9. In Rosenthal and Fode's study, students training 'maze-bright' rats got better results than those training 'maze-dull' rats, even though all rats were genetically similar. This demonstrates:
A. Random assignment failed
B. Experimenter expectancy effects where experimenters' expectations unintentionally influence results
C. That genetic factors are more important than training
D. A placebo effect in animal research
Answer Key with Explanations
1. B - Experiments involve the manipulation of an independent variable by the researcher
The defining characteristic of an experiment is that the researcher actively manipulates the independent variable and then observes the effect on the dependent variable. This manipulation, combined with control and random assignment, allows researchers to draw causal conclusions.
2. B - Varies systematically with the independent variable
A confounding variable is an extraneous variable that differs on average across levels of the independent variable. For example, if participants in one condition have substantially higher IQs on average than participants in another condition, then IQ would be confounding because it varies systematically with the conditions. However, if IQ varies randomly across conditions (some high, some low in each), it's merely extraneous. The systematic variation is what makes confounding variables problematic.
3. B - The improvement could be due to placebo effects rather than the therapy itself
Placebo effects are often driven by expectations which poses a serious problem for researchers who want to determine whether a treatment works. An alternative is using a placebo control condition.
4. B - Only one level of the independent variable
In a between-subjects (or between-groups) design, each participant is assigned to only one condition or level of the independent variable. Different groups of participants experience different conditions, and performance is compared across groups.
5. B - The number of possible orders increases factorially (e.g., 6 conditions = 720 orders)
Factorial growth (calculated as n!, where n is the number of conditions) makes complete counterbalancing impractical with many conditions. Latin square designs are a more efficient way of counterbalancing that require far fewer orders.
6. C - External validity (generalizability)
External validity refers to the extent to which research findings generalize beyond the specific study context to other settings, populations, and times. Concerns about the artificial laboratory environment and participants' awareness suggest the findings may not generalize to real-world settings, which is an external validity issue.
7. B - The psychological process of self-objectification likely operates in various situations, giving it psychological realism
At first, this manipulation might seem silly. When will undergraduate students ever have to complete math tests in their swimsuits outside of this experiment? However, the process of self-objectification and its effect on attention is likely to operate in a variety of situations. Psychological realism can have value even when mundane realism is lacking.
8. B - When the researcher wants to verify that the independent variable manipulation had its intended psychological effect on participants
A manipulation check is used to verify that the manipulation of the independent variable actually had the intended effect. For example, if you manipulate anxiety, you might include a manipulation check to confirm participants in the high-anxiety condition actually experienced more anxiety than those in the low-anxiety condition.
9. B - Experimenter expectancy effects where experimenters' expectations unintentionally influence results
Although the rats were genetically similar, some of the students were told that they were working with "maze-bright" rats that had been bred to be good learners, and other students were told that they were working with "maze-dull" rats that had been bred to be poor learners. Over five days of training, the "maze-bright" rats made more correct responses, made the correct response more quickly, and improved more steadily. The students' expectations about how the rats would perform made the difference and demonstrates how experimenters' expectations can unintentionally influence results—an experimenter expectancy effect.