Alvin Poyser
PAM 210
Prelim 2
Chapter 2:
Association
two variables are assoc. if some values of one variable tend to occur more often with some values of the
other variable.
Response variable
 measures an outcome of a study.
Explanatory variable
explains or causes changes in the response variables.
Scatter plots:
•
Outlier: An individual observation that falls far away from the pattern.
•
Positive relationship
:
Above average values of one variable tend occur with above average values of the other
variable
and
below average values of one variable also tend to occur with below average values of the other
variable.
•
Negative relationship
:
Above average values of one variable tend to occur with below average values of the
other variable and vice versa.
Correlation coefficient
(
r
) gives us a numerical measurement of the strength of a linear relationship between the
explanatory and response variables
•
Correlation does not distinguish between response and explanatory variables.
•
Both variables
must be quantitative
.
r
does not depend on units of measurement
Values of r are always between 1 and 1
r
is greatly affected by extreme values or outliers
Least sqr regressions: we have a bunch of observations on an explanatory variable,
x
, and a response variable,
y.
We need to find the line: y= a+bx
(a, is intercept, b is slope)
2 types of prediction are
…
In sample
: For a value of the explanatory variable that is within the observed range of that
variable, but not actually observed.
& Out of sample
: For a value of the explanatory variable that is outside of the range
of values actually observed. This is usually referred to as
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 Fall '08
 ABDUS,S.
 Normal Distribution, Variance, average values

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