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Stat ref sheet

# Stat ref sheet - Least squares regression equation y=a bx...

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Least squares regression equation: y=a+bx b=r(Sy/Sx) a=y-bx R^2 – x% of variation in Y can be explained by X 5 study elements: object of study, observational or experimental, how individuals are selected, how many individuals, what variables are measured. The best (and only?) method of clearly establishing causation is to conduct a carefully- designed randomized experiment that changes X, the explanatory variable, and observes the effect on Y Block design: matched pairs – assign individuals to a group, then pair them according to strata, and compare results. Right skewed = tail goes to the right 68-95-99.7 50% of observations are smaller than the median and 50% are larger than the median The variance (standard deviation) is sensitive to skew and outliers, the IQR is not • An outlier has no affect on the computation of IQR because it doesn’t change Q1or Q3 • The variance (standard deviation) makes efficient use of the data –especially if it is mound shaped
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