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29 Cards in this Set
- Front
- Back
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Positive association
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slopes upward to the right, the y-coordinates of the points tending to increase with their x-coordinates.
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Point of averages
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point showing the average of the x-values and the average of the y-values (locates the center of the cloud)
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Most of the points will be within __ vertical and horizontal SDs on either side of the point of averages
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2
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The correlation coefficient (r) measures ________ _______ _ ____
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clustering around a line
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The relationship of two variables can be summarized by:
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-average and SD of the x values
-average and SD of the y values -correlation coefficient |
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Negative correlation:
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As one variable decreases the other decreases as well
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Correlations are always between
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-1 and 1
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The SD line goes through ....
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the point of averages and all points which are an equal number of SDs away from the average for both variables
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What is the slope of the SD line?
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(SD of y) / (SD of x) when its positive, if negative tack on a minus sign
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Procedure for computing the correlation coefficient
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-convert each variable to standard units
-subtract the average found in the SD equation from each value and divide by the SD to find each x value in standard units -repeat for y -multiply each pair for -average of the products gives the correlation coefficient |
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r=
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average of (x in standard units) x (y in standard units)
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The relationships between 2 variables can be represented by a ______ ________
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scatter diagram
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The correlation coefficient is a pure number without ____
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units
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Correlation coefficient is not affected by:
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-interchanging the two variables
-adding the same number to all the values of one variable -multiplying all the values of one variable by the same positive number |
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The correlation coefficient can be misleading in cases of _______ and ___________
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outliers and nonlinearity
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Points can be rejected from a study only if there is a good reason to do so
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.
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r measures _______ association, not association in general
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linear
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Ecological correlations are based on rates or averages
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tend to overstate the strength of association for individuals
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Correlation measures _______.
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association
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Association is not the same as ________.
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Causation
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Correlation coefficient measures clustering around a line, relative to the _____
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SD's
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The regression line for y on x estimates the average value for ___ corresponding to each value of ___
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y,x
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Regression method
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Associated with each increase of one SD in x there is an increase of only r SDs in y, on the average
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The regression line is a smoothed version of the graph of ______
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averages
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Regression method:
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In virtually all retest situations, the bottom group on the first test will on average show some improvement on the second test and the top group will on average fall back
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Regression Fallacy
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Thinking that the regression effect must be due to something important, not just the spread around the line
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observed test score=
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true score + chance error
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associated with an increase of one SD in x, there is an increase of only r SDs in y, on the average
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.
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If the graph of averages has a strong non-linear pattern, regression may be inappropriate
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