Two basic types

1
Statistics

• Two basic types
• Descriptive
• Describes the nature and properties of the data
• Helps to organize and summarize information
• Inferential
• Used in testing hypothesis
• (e.g., differences between groups, relationships
  between variables)

2
Describing Individual Differences

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

3
Descriptive Statistics

• 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

4
Descriptive Statistics

• Measures of Variability
• Range
• subtract the lowest from the highest score and
  add 1
• Standard Deviation
• measure of the spread of the scores around the
  mean

5
Calculating the standard deviation
1.58
6
Frequency Plots
Frequency Distribution
7
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

8
Normal Distributions

• 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)

9
(No Transcript)
10
Correlation

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

11
Positive Correlation
r .95
12
No Correlation
r .00
13
Negative Correlation
High
r -.95
Low
Low
High
14
Data Set 3 Example Scatter Plot
15
(No Transcript)