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# Chapter 8 (3-4), 9 - PowerPoint PPT Presentation

Chapter 8 (3-4), 9. More about Correlation. Today’s Lecture. SD Line Calculating r correlation vs causation. The SD Line. the line the points cluster around passes through the point of averages: (AVGx , AVG Y ) Has slope : . Calculating r (call variables “X” and “Y”).

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## PowerPoint Slideshow about ' Chapter 8 (3-4), 9' - zinna

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### Chapter 8 (3-4), 9

• SD Line

• Calculating r

• correlation vs causation

• the line the points cluster around

• passes through the point of averages: (AVGx , AVGY)

• Has slope :

Calculating r(call variables “X” and “Y”)

• Step 1: Calculate AVGx and AVGy

• Step 2: Calculate SDx and SDy

• Step 3: Standardize each variable

• Step 4: Find average of products of z-scores (standard scores)

NOTE: The Correlation Coefficient is unaffected if the units of measurement are changed

Example:

Correlation between height and weight remains the same whether height is measured in inches, cm., feet, etc.

Important Note: Correlation DOES NOT Imply Causation

• strong association between 2 variables is not enough to justify conclusions about cause and effect

Strong association between:

• number of firefighters and amount of damage

• Does sending more firefighters cause more damage?

• shoe size and score on a reading comprehension exam for elementary school children

• What’s the explanation?

• SAT and GPA scores

• What’s the explanation?

Important Note: Correlation DOES NOT Imply Causation

• strong association between 2 variables is not enough to justify conclusions about cause and effect

• best way to get evidence that X causes Y is through a controlled experiment