Overview of experimental research

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Overview of experimental research

• How it differs from descriptive research
• Manipulation of variables
• Cause and effect
• General logic behind experiment
• Two or more groups
• On average as similar as possible
• Manipulation performed on one group
• Example Study by Simpson and Clark Effects of
  THC (active ingredient in marijuana) on memory

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Components of an experiment

• Independent and dependent variables
• Variables in our example
• Control and experimental group
• How do they differ
• How are subjects assigned
• Importance of random assignment

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Why is randomization your friend

• Best way to make it so that ON AVERAGE the
  control and experimental groups are as similar as
  possible on any given measure
• Not a guarantee
• Not randomizing introduces potential confounds
• Example Suppose didnt randomize in THC study
• Imagine following data
• Average weight of control group 150 lbs
• Average weight of experimental group 190 lbs
• Experimental group remembers 2 items more than
  control
• Manipulation of THC confounded with weight

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Randomization example
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Analyzing results

• Once data is collected (both descriptive and
  experimental) need to be analyzed
• Measures of central tendency
• Purpose
• Mean
• Median
• Mode
• Measures of variability
• Range
• Standard deviation

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Understanding standard deviations

• On average, how much does each score differ from
  the mean?
• First find mean of a set of scores
• Next subtract each score in the set from the mean
• Square each difference (gets rid of negative
  numbers)
• Add all the squared differences (analogous to
  computing mean)
• Divide by 1 less than total number of scores
• Take the square root of the result

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Example

• Scores on first exam 10, 40, 90, 50
• First find mean (10 40 90 50)/4 47.5
• Subtract mean from each score then square
• (10 47.5)2 (40-47.5)2 (90-47.5)2
  (50-47.5)2 3275
• 3275/3 1091.6
• Square root of 1091.6 33
• Standard deviation of the above scores is about
  33

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Importance of standard deviation

• Standard deviation tells how variable your data
  set is
• When you report a mean MUST MUST report standard
  deviation
• The standard deviation tells you how
  representative the mean is of your data set
• The effects of outliers on the mean

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Deciding whether to curve exam

• Exam 1 10, 10, 10, 50 Mean 20
• Exam 2 10, 20, 25, 25 Mean 20
• Conclusion? Because means are the same must
  either curve both or curve neither. Sorry no
  curve
• Standard deviation exam 1 20
• Standard deviation exam 2 7
• Relationship between mean and standard deviation

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Summary

• Psychology is a science because relies on
  scientific method
• Importance of data collection
• Descriptive methods of collecting data
• Naturalistic observations, case studies,
  interviews, surveys, correlations
• Experiment as method for gathering data
• Independent and dependent variables
• Control and experimental group
• Random assignment
• Data analysis
• Measures of central tendency
• Measures of variability

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Ethics in research
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General ethical guidelines

• Do no harm
• Principle of informed consent
• Participation is voluntary
• No coercion
• Free to withdraw
• Compensation is NOT contingent on completion
• Importance of debriefing

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Who enforces the guidelines

• Institutional review board (IRB) at each
  University
• Professional societies
• APA, APS
• Journals
• Granting agencies
• NIH, NSF

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What about studies using animals

• Why use animals
• Need to protect physical comfort/health of
  animals
• What about psychological health of animals
• Example of Harlowe and importance of comfort vs.
  sustenance
• Get all food from wire mother
• Allowed to spend as much time with cloth mother
  as want

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