Correlations and Regressions

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  • Correlation and Regression
    • Correlation
      • for positive correlation the points on the scatter diagram increase as you go from left to right.
      • for a negative correlation the point on the scatter diagram decrease as you from left to right.
      • r is a measure of linear relationship
        • r=1 perfect positive linear correlation
        • r= -1 perfect negative correlation
        • r=0 no linear correlation
      • Coding
        • you can rewrite the variable x and y using coding
        • r is not affect by coding
    • Regression
      • the equation of the regression line of y on x
        • y = a +bx
        • where b =Sxy / Sxx
        • a =  ?y  -b ?x
      • Coding
        • to turn a coded regression line in to an actual regression line substitute the codes into the answer
      • the purpose of the regression line is to make predictions about values of one variable for some given values of the other
      • predictions should only be made in the range of the data
        • extrapolaion are predictions made outside the range of data and are unreliable
      • outliers do effect the regression line

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