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14 Cards in this Set

  • Front
  • Back

Scatter plot

a collection of set data points, one data point per person or object.

If there is a clear relationship, quantities are said to be ...

correlated

Correlation is used to determine...

if there is a relationship between two variables and, if so, the strength and directions of that relationship

A line that fits the data points in a scatter plot is called a ...

regression line

Correlation Coefficient

A measure that is used to describe the strength and direction of a relationship between variables whose data points lie on or near a line

Correlation coefficient is designated by

r

Variables are _________ if they tend to increase or decrease together

positively correlated

Variables are negatively correlated if

one variable tends to decrease while the other increases

Perfect positive correlation

all points in the scatter plot lie precisely on the regression line that rises from the left to the right

Perfect negative correlation

all points in the scatter plot lie precisely on the regression line that falls from the left to the right

Correlation coefficient formula

r = n(sum of xy) - (sum of x)(sum of y)




divided by




square root of n(sum x squ)-(sum x) squ times square root of n(sum y squ) - (sum y)squared

When computing correlation coefficient by hand, organize work in 5 columns ...

x y xy x squared y squared




in graph form, bottom of graph will have:




sum of x's, sum of y's, sum of xy's, sum of x squareds, sum of y squareds

Writing the equation of the regression line by hand

-- y=mx + b




-- m= n(sum xy) - (sum x)(sumy)




divided by




(n(sum x squared) - (sum x) squared




-- b = sum y - m(sum x)




divided by


n

Significance level of 5% or 1% or... ex:

determines if variable correlation is not related to the population