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Cause and Effect Chapter 3, section 3.4. Determining if a correlation exists is only the first step in a statistical analysis More important than if a relationship exists is why it exists. Cause and Effect Relationship.
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Determining if a correlation exists is only the first step in a statistical analysis • More important than if a relationship exists is why it exists
Cause and Effect Relationship • A change in one variable (independent) produces a change in another variable (dependent) Examples: • Lowering interest rates causes people to invest more money • Carbon dioxide in the atmosphere causes an increase in the global temperature
Cause and effect relationships are nice because if we want to change the dependent variable we know we can produce this by changing the independent variable • Sometimes there is a correlation between two variables but this is not a result of a cause and effect relationship.
Common Cause Factor • An external variable is causing the two variables to change in the same way Examples: • The number of cases of frostbite increases as the sales of winter tires increases
Reverse Cause and Effect Relationship • The independent and dependent variables are reversed Examples • Crime rates rise as the number of people in prison rise so someone argues that releasing all the criminals will decrease the crime rate • The mayor who orders his citizens to celebrate before the World Series so their team will win
Accidental Relationship • There is a correlation between two variables but it is just a coincidence Example • The unemployment rate is increasing at the same time that the Blue Jays go on a winning streak
Presumed relationship • The relationship does not seem to be accidental but it is difficult to show a cause and effect or common cause relationship Example • Heart attack rates drop as fitness clubs bring in more revenue
Extraneous Variables • External variables that affect either the independent or dependent variable (or both) • These may make it difficult to determine if a causal relationship exists Example: What type of relationship would you expect to see between your term mark in data and your exam mark? Possible external variables: -you have a Calculus exam on the same day as data -you play on the rugby team and you have to go to OFSAA the week before exams