a typical experiment

1
a typical experiment

• prototype of a controlled laboratory
  investigation

2
In the most typical experiment

• Subjects are randomly assigned to a treatment
  or control group.
• The treatment group is exposed to the
  experimental stimulus.
• The control group is not exposed to the
  experimental stimulus
• The researcher measures any resulting differences
  between the treatment and control group

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Example 1 treatment group versus control group

• RQ Does caffeine consumption increase physical
  stamina?
• Independent variable caffeine consumption versus
  no caffeine consumption
• Dependent variable physical stamina as measured
  by the total distance jogged on a treadmill in 1
  hour.

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Random assignment

• Random assignment produces equivalent groups for
  comparison purposes
• 200 volunteers are randomly assigned to a
  treatment group or control group

N 200
treatment group 100
control group 100
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Operationalization of the independent variable

• treatment group
• Consumes 12 oz. (500 milligrams) of coffee just
  before jogging on a treadmill

• control group
• Consumes 12 oz. Of decaffeinated coffee just
  before jogging on a treadmill

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Measurement of the dependent variable

• The total distance of each jogger is measured by
  the treadmills counter to the nearest 1/10 mile.
  There is a 1 hr. time limit. Two observers
  watch to ensure the joggers are jogging (8-12
  minute pace), not walking, until they stop.
• The average distance of the joggers in the
  treatment group is compared with the average
  distance of joggers in the control group.

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Example 2 comparison groups

• RQ Do dog owners report greater relationship
  satisfaction than cat owners?
• Independent variable pet ownership, e.g., dogs
  owners versus cat owners
• Dependent variable relationship satisfaction, as
  measured by the Dyadic Adjustment Scale.

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Non-random assignment

• Some experiments rely on intact or
  self-selected groups
• People already own their pets. They cant be
  randomly assigned to own one pet or another

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Operationalization of the independent variable

• 91 dog owners are selected using a mall
  intercept technique
• The dog owners do not own a cat or any other pets.

• 103 cat owners are selected using a mall
  intercept technique
• The cat owners do not own a dog or any other pets.

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Measurement of the dependent variable

• All of the respondents are asked to complete the
  Dyadic Adjustment Scale
• a paper-pencil survey that asks respondents to
  rate the quality of their relationship with a
  significant other.
• The average ratings of the dog owners are then
  compared with the average ratings of the cat
  owners to see if there is a significant
  difference.