What does

1
What does correlation mean?

• There is a positive correlation between average
  family income and MCAS passing rate.
• There is a negative correlation between family
  income and dental problems.
• There is a positive correlation between income
  and education.
• There is no correlation between shoe size and
  SAT scores.

Can your group define or explain correlation
with a picture or a few words?
2
Scatterplots for Correlation

• Which picture shows income and education? Income
  and dental problems? Shoe size and SAT scores?

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Note! We have an x and a y here, but we arent
asking whether x causes y.
3
What does correlation tell us?

• Does a higher family income cause higher MCAS
  scores or do higher MCAS scores cause higher
  family income?
• Could it be that something else makes income
  higher AND makes MCAS scores higher?

Can your group ask questions, be willing to
wonder, think of alternative explanations?
4
What does correlation tell us?

• Does a lower family income cause more dental
  problems or do more dental problems cause family
  income to fall?
• Could it be that something else is caused by
  lower income AND causes dental problems?
• Could it be that having a higher income causes
  something else to happen that prevents dental
  problems?

Can your group ask questions, be willing to
wonder, think of alternative explanations?
5
What does correlation tell us?

• Does education increase income or does income
  increase education? Could both be true?
• Could there be something that causes both income
  and education to increase?
• Could there be something that causes both income
  and education to decrease?

Can your group ask questions, be willing to
wonder, think of alternative explanations?