Pullbacks are widely seen as buying opportunities after a security has experienced a large upward price movement. They shouldn’t be confused with reversals, which tend to be longer term downtrends where there has been a change in fundamentals. Traders should be sure to use technical analysis to verify that a pullback remains above key support levels to avoid possible longer term reversals that could result in losses.

The very simplest case of a single scalar predictor variable * x* and a single scalar response variable * y* is known as * simple linear regression * . The extension to multiple and/or vector -valued predictor variables (denoted with a capital * X* ) is known as * multiple linear regression* , also known as * multivariable linear regression* . Nearly all real-world regression models involve multiple predictors, and basic descriptions of linear regression are often phrased in terms of the multiple regression model. Note, however, that in these cases the response variable * y* is still a scalar. Another term * multivariate linear regression* refers to cases where * y* is a vector, ., the same as * general linear regression* .

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