chapter 5 linear models linear models are studied intensively because: easiest to understand and...

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Chapter 5 Linear Models Linear Models are studied intensively because: •Easiest to understand and analyze •Relationships are often linear •Variables with non-linear relationship can often be transformed into linear relationship through an appropriate transformation •Even when a relationship is non-linear, a linear model may provide an accurate approximation for a limited range of values.

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Page 1: Chapter 5 Linear Models Linear Models are studied intensively because: Easiest to understand and analyze Relationships are often linear Variables with

Chapter 5 Linear Models

Linear Models are studied intensively because:

•Easiest to understand and analyze•Relationships are often linear•Variables with non-linear relationship can often be transformed into linear relationship through an appropriate transformation•Even when a relationship is non-linear, a linear model may provide an accurate approximation for a limited range of values.

Page 2: Chapter 5 Linear Models Linear Models are studied intensively because: Easiest to understand and analyze Relationships are often linear Variables with

5 Linear Models

• Least Square Line: • Let X and Y be two quantitative variables.• Let (x1, y1), (x2, y2), …, (xn, yn) be data

points collected on n individuals

• Goal: Find a linear model in the form Y = a + b X

that represents the given data set

Page 3: Chapter 5 Linear Models Linear Models are studied intensively because: Easiest to understand and analyze Relationships are often linear Variables with

5 Linear Models

Page 4: Chapter 5 Linear Models Linear Models are studied intensively because: Easiest to understand and analyze Relationships are often linear Variables with

5 Linear Models

Page 5: Chapter 5 Linear Models Linear Models are studied intensively because: Easiest to understand and analyze Relationships are often linear Variables with

5 Linear Models

Page 6: Chapter 5 Linear Models Linear Models are studied intensively because: Easiest to understand and analyze Relationships are often linear Variables with

5 Linear Models

Formulas for computing b and a

• b = Sxy/Sxx

• a = average(y) – b average(x)

• Sxy = Sum(xy) –Sum(x)Sum(y)/n• Sxx = Sum(x^2) –(Sum(x))^2/n

Page 7: Chapter 5 Linear Models Linear Models are studied intensively because: Easiest to understand and analyze Relationships are often linear Variables with

5 Linear Models

• Remarks:

• 1. Use linear regression if the scatter plot looks reasonably straight

• 2. Check for outliers which could drastically influence regression lines

• 3. If data seem to cluster in scatter plot, look data more carefully

• 4. Large magnitude of slope indicates steeper line• 5. Negative slope shows negative association• 6. Positive slope shows positive association