STA215H5 Lecture Notes - Lecture 7: Standard Deviation, Scatter Plot, Simple Linear Regression

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1 Jun 2018
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STA215; Chapter 7
What is Linear Regression?
ā—Linear Regressionī€ is a linear approach to modelling the relationship between the
response variable and one or more explanatory variables.
ā— The case of one explanatory variable is called ī€simple linear regression
ā— Example;
ā—‹ Suppose we find that how long running shoes last is related to how much they
cost BUT we want to know how long a pair of running shoes are expected to
last if we pay $55?
ā—‹ Correlation alone wonā€™t answer this question. - Instead, we need a model!!
ā—‹ In particular, we need a model to be able to use one variable to predict the
other.
ā—‹ The solution: Linear Regression!
ā— Regression Line
ā—‹ A ī€regression lineī€ is a straight line that describes how a response variable, y,
changes as an explanatory variable, x ,changes.
ā—‹ We can use a regression line to predict the value of y for a given value of x.
ā— Equation of Straight Line
ā—‹ A straight line relating y (response variable) to x (explanatory variable) has an
equation of the form: ī€y = ax + b
ā—‹ Where;
ā– a is the slope,ī€ the amount by which y changes when x increases by
one unit
ā– b is the interceptī€ and corresponds to the value of y when x=0
ā— Example;
ā—‹ Using our motivating example from slide 3, we expect that how long running
shoes last is related to the cost. Data collected from 100 elementary school
students was used to develop a model for this relationship and the following
was obtained:
ā–  Amount of time running shoes last (hours) = 15.34 + 35.02 x price of
running shoes (dollars)
ā—‹ a) What is the slope of this line? Say in words what this value means.
ā–  The slope is 35.02. This means on average, the amount of time shoes
last increases by 35.02 hours for every dollar increase in price
ā—‹ b) What is the intercept? Explain why the value of the intercept is not
statistically meaningful.
ā–  The intercept is 15.34. This is the amount of time running shoes that
cost $0 last. Even though this interpretation is valid, such prediction
would not make sense because shoes are not free...unfortunately
ā—‹ c) Find the predicted amount of time running shoes that cost $55 will last
ā–  For shoes that cost $55, we predict they will last: 1,941.44 hours 15.34
+35.02(55) = 1,941.44 hours
ā— Example;
ā—‹ Suppose you have a lucky pencil and only use that pencil everyday. It initially
weighed 5 grams when you first bought it. Itsā€™ weight goes down 0.004 grams
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Document Summary

What is linear regression? response variable and one or more explanatory variables. Linear regression is a linear approach to modelling the relationship between the. The case of one explanatory variable is called simple linear regression. In particular, we need a model to be able to use one variable to predict the other. A regression line is a straight line that describes how a response variable, y, We can use a regression line to predict the value of y for a given value of x. changes as an explanatory variable, x ,changes. A straight line relating y (response variable) to x (explanatory variable) has an equation of the form: y = ax + b. A is the slope, the amount by which y changes when x increases by. B is the intercept and corresponds to the value of y when x=0 one unit.

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