POLI 30 Lecture Notes - Lecture 11: Standard Deviation, Scatter Plot
Document Summary
Lecture eleven: scatterplots and correlation pt. 1 02/20/19. Additional variables/dimensions may be shown with color, symbols, or animation. Single number that describes the direction and strength of a straight line relationship between two quantitative variables: r. The word correlation is often used more loosely to describe any multivariate pattern, but here we have a very precise meaning. Sx and sy: standard deviation of x and y. Sigma means do this for each observation then add them up. The correlation coefficient doesn"t care about the units in which you measure your variables. It will be the same regardless of how you measure. For each variable we subtract the mean, centering it on zero, then divide the whole thing by the standard deviation of each variable. Calculate mean of x and of y. Calculate standard deviation of x and of y. Multiply (x-mean(x)) by (y- mean(y)) for each observation. R tells you the direction of the relationship (positive or negative)
