Descriptive Statistics Numerical Methods：描述性统计数值方法.ppt

* * * * * * * * * * * * * * * * * * * 3-* Outliers Outliers are measurements that are very different from other measurements They are either much larger or much smaller than most of the other measurements Outliers lie beyond the limits of the box-and-whiskers plot Measurements less than the lower limit or greater than the upper limit LO3-4 3-* 3.4 Covariance, Correlation, and the Least Squares Line (Optional) When points on a scatter plot seem to fluctuate around a straight line, there is a linear relationship between x and y A measure of the strength of a linear relationship is the covariance sxy LO3-5: Compute and interpret covariance, correlation, and the least squares line (Optional). 3-* Covariance A positive covariance indicates a positive linear relationship between x and y As x increases, y increases A negative covariance indicates a negative linear relationship between x and y As x increases, y decreases LO3-5 3-* Correlation Coefficient Magnitude of covariance does not indicate the strength of the relationship Magnitude depends on the unit of measurement used for the data Correlation coefficient (r) is a measure of the strength of the relationship that does not depend on the magnitude of the data LO3-5 3-* Correlation Coefficient Continued Sample correlation coefficient r is always between -1 and +1 Values near -1 show strong negative correlation Values near 0 show no correlation Values near +1 show strong positive correlation Sample correlation coefficient is the point estimate for the population correlation coefficient ρ LO3-5 3-* Least Squares Line If there is a linear relationship between x and y, might wish to predict y on the basis of x This requires the equation of a line describing the linear relationship Line is calculated based on least squares line Discussed in detail in a later chapter Need to find slope (b1) and y-intercept (b0) LO3-5 3-* 3.5 Weighted Means and Grouped Data (Optional) Sometimes, some measurements are more important than others