Introduction section of article

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Introduction section of article

• Purpose of study and research question(s)
• Problems related to study topic
• Literature review
• Rationale (justification) for the study
• Hypotheses

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Experimental Research
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Example
Objective To find out the impact of sunshine on
plants growth.
Treatment
I.V.
I.V.
Experimental
Control
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Experimental Research

• Researchers manipulate independent variable - 2
  levels
• And measure the other (dependent variable)
• Give treatment to participants and observe if it
  causes changes in behavior
• Compare experimental group (w/ treatment) with a
  control group (no treatment)
• Can say IV caused change in the DV

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Experimental research design

1. Measure dependent variable
2. Control extraneous variables
3. Hold constant
4. The only difference between experimental group
   and control group is the manipulated variable.
5. Treat groups equally except for treatment.
6. Randomize effects across treatments
7. Design to eliminate alternative explanations

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• Random Assignment
• A way to assign participants in your sample to
  the various treatment conditions (groups that
  will receive different level of the IV)
• Any member of your sample has equal chance of
  being assigned in any treatment group

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Control Variable

• The variable that you would like to keep constant
  in order to clarify the relationship between
  Dependent Variable and Independent Variable
• Confounding variable (if not controlled)

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Internal Validity

• Ability of your research design to adequately
  test your hypothesis
• Showing that variation in I.V. CAUSED the
  variation in the D.V. in experiment
• In correlational study,
• Showing that changes in value of criterion
  variable relate solely to changes in value to
  predictor variable

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Example -- Design

• Question Does new teaching method work better
  than traditional method in intro psych course?
• Method Teaches class in morning using new
  method.
• Teaches afternoon class using traditional method.
• Both classes will use same book, tests, etc.

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Findings

• Students exposed to new method have higher
  grades.
• Concludes New method better.
• Justified?
• Why or why not?

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Confounding

• Whenever 2 or more variables combine in a way
  that their effects cannot be separated
  confounding.
• Thus, the teaching method study as designed lacks
  internal validity.

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Threats to Internal Validity -- 7 Sources of
Confounding

• Campbell Stanley (1963)
• History
• Other events occur that affect results
• Maturation
• Effect of age or fatigue
• Testing

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Threats to validity continued

• Instrumentation
• Changes in criteria used by observers or
• instrument - (is scale set to 0?)
• Statistical regression
• If participants selected cause of extreme scores,
  will tend to be closer to average of pop. upon
  re-measure.

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Threats to internal validity cont.

• Biased selection of subjects
• If participants differ in ways that affect their
  scores on DV
• Experimental mortality
• People drop out of study due to frustration, etc.
  those that remain differ than drop outs.

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Completely randomized

• Independent groups
• Completely randomized 2-group experimental design
• Advantages
• no pretesting or categorizing of participants
• adequate to test hypothesis

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2-Treatment Within-Subjects Design

• Repeated measures
• Randomly assign participants to different
  treatment groups,
• Each participants performance is measured under
  Treatment A and again under Treatment B
• Advantages reduce error variance
• Disadvantages - attrition, carryover effects

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2-treatment within-subjects matched design

• Repeated measures
• When participant characteristic correlates w
  Dependent Variable
• Assess the participants for the characteristics
• Group participants w/ matching characteristics.
• Matched sets of participants distributed at
  random, one per group.
• Advantages - Effect of error ?, effect of
  characteristic distributed evenly across
  treatment groups.

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Carryover effects

• First treatment alters the behavior observed in
  next treatment
• Sources
• learning
• fatigue
• habituation - repeated exposure -- reduced
  responsiveness
• To ?effect - (breaks between treatments, change
  treatment order)