Describing Behavior

1
Describing Behavior

• Chapter 4

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Data Analysis

• Two basic types
• Descriptive
• Summarizes and describes the nature and
  properties of the data
• Inferential
• What is the likelihood the results in the sample
  actually occur in the population
• (e.g., differences between groups, relationships
  between variables)

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Describing Individual Differences

• Measures of Central Tendency
• Measures of Variability
• Distribution of the data

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Measures of Central Tendency

• Mean
• average score of all observations in distribution
• Median
• midpoint of all scores in distribution
• Mode
• most frequently occurring score in distribution

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Measures of Variability

• Range
• subtract the lowest from the highest score
• Standard Deviation
• measure of the spread of the scores around the
  mean
• Variance
• square of the standard deviation

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Calculating the standard deviation
1.58
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Data Distributions
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Descriptive Statistics

• Distribution of the data
• Shapes of distribution curves
• Bell (normal distribution)
• The bell curve has desirable statistical
  properties
• A number of inferential statistics assume data
  is normally distributed
• Skewed Curves
• Negative Skew - tail of the curve is to the left
• Positive Skew - tail of the curve is to the right

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Properties of a Normal Distribution

• Measures of central tendency are the same
• mean median mode
• We know percentage of scores that fall within
• ? 1 standard deviation (68)
• ? 2 standard deviations (95)
• ? 3 standard deviations (99)

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Correlation

• The extent to which one variable can be
  understood on the basis of another
• Properties of correlation coefficient
• direction (positive or negative)
• magnitude (strength of the relationship)

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Positive Correlation
r .95
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No Correlation
r .00
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Negative Correlation
High
r -.95
Low
Low
High
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Correlation A Review
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Distribution for Example
M 3.00 SD 1.10