Description and Correlation

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Description and Correlation

• Psych 7
• March 6th

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Reminder

• The last day to participate in experiments is
  THIS FRIDAY (MARCH 9TH)!!
• If you are writing a paper, it is due THIS FRIDAY
  by 5pm
• Give to Chris McFerron in Room 1813

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Outline

• What are statistics?
• Analyzing your results
• Frequency Distributions
• Measures of Central Tendency and Variability
• Correlations

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What are Statistics?

• A set of mathematical procedures for summarizing
  and interpreting observations (data)
• Goals

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Two Kinds of Statistics

• Descriptive Statistics
• Inferential Statistics

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Analyzing your Results

• 3 Basic Ways to Describe Results
• Compare group percentages
• Correlate scores of individuals on 2 variables
• Compare group means

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Compare Group Percentages

• How often do you wash your hands after using the
  bathroom?
• Always Sometimes Never
• Gender who said Always
• Female 82
• Male 79

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Compare Group Percentages, cont.

• I get cravings for chocolate
• Never Sometimes Fairly Often All
  the Time
• Gender who said Fairly Often or All the
  Time
• Female 60
• Male 15

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Correlate Scores

• Is stress correlated with chocolate cravings?
• When you are stressed, how likely are you to eat
  more than usual?
• 1 (Very unlikely) 7 (Very likely)
• I get cravings for chocolate
• Never Sometimes Fairly Often All
  the Time

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Correlate Scores, cont.

• Does waiting to have sex correlate with the
  number of sexual partners one has?
• I think it is acceptable to have more than one
  sexual relationship at a time.
• Strongly Disagree Disagree Undecided Agree
  Strongly Agree
• Approximately how long do you wait before having
  sex with a person you are romantically involved
  with?
• ____until marriage
• ____5 years
• ____3 years
• ____1 year
• ____1 week
• ____1 day

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Compare Group Means

• On average, how many minutes per day do you spend
  taking a shower? ____________

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Compare Group Means, cont.

• How many pairs of underwear do you own? _________

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Frequency Distributions

• Different Types of Frequency Distributions
• Table
• Pie Charts
• Bar Graphs
• Frequency Polygon

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Frequency Distributions Table

• When looking for a mate, I consider the following
  qualities most important

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Frequency Distributions Pie Chart

• When looking for a mate, I consider the following
  qualities most important.

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Frequency Distributions Bar Graph

• When looking for a mate, I consider the following
  qualities most important.

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Frequency Distributions Polygon

• When looking for a mate, I consider the following
  qualities most important.

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Measures of Central Tendency and Variability

• Central Tendency
• Mean, median, mode
• Variability
• Range and standard deviation

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Measures of Central Tendency

• Mean
• Computed by summing scores and dividing the sum
  by the number of individuals
• Median
• The score or point in the distribution above
  which half of the scores lie
• Rank order the scores and select the middle score
• Mode
• The score that occurs most frequently

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Measures of Central Tendency Example

• Consider the following set of reading scores for
  15 second graders
• 31 33 35 38 40 41 41 41 44 46 47 48
  49 49 51
• Mean 42
• Median ?
• Mode ?

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Measures of Central Tendency When to Use

• Now consider the following set of reading scores
  for 15 second graders
• 31 33 35 38 40 41 41 41 44 46 47 48
  49 98 99
• Mean 48
• Median 41
• Mode 41

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Measures of Central Tendency When to Use, cont.

• It depends on the type of data you are
  describing
• Mean
• Median
• Mode

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Measures of Variability

• Range
• Standard Deviation

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Measures of Variability Example

• Here are the heights for two groups of men

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Correlations

• A statistical value that assesses the
  relationship between 2 variables
• More specifically
• The direction of the relationship (/-)
• The form of the relationship (straight,
  curvilinear)
• The degree or strength of the relationship (-1 to
  1)
• Small relationship .10 - .20
• Medium relationship .30
• Large relationship gt.40

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Graphing Correlations
C
A
D
B
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Another Correlation from the Class Survey

• Do you think there is a relationship between the
  following items?
• I enjoy watching movies like The Notebook.
• I am concerned with how much I weigh.

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Tuesday

• Statistical Inference
• Cozby, Chapter 13