BIOSTATISTICS Linear regression. Copyright ©2011, Joanna Szyda INTRODUCTION 1.Linear regression equation 2.Estimation of linear regression coefficients.

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Presentation transcript:

BIOSTATISTICS Linear regression

Copyright ©2011, Joanna Szyda INTRODUCTION 1.Linear regression equation 2.Estimation of linear regression coefficients Least squares Weighted least squares 3.Examples of regression equations Multiple regression Polynomials Logarithmic regression 4.Results interpretation

LINEAR REGRESSION EQUATION

Copyright ©2011, Joanna Szyda REGRESSION EQUATION 1.Dependent variable 2.Independent variable BODY WEIGHT ADIPOSE TISSUE DATA SET

Copyright ©2011, Joanna Szyda REGRESSION EQUATION INTERCEPT

Copyright ©2011, Joanna Szyda REGRESSION EQUATION x i -x i-1 y i -y i-1 slope

Copyright ©2011, Joanna Szyda no dependence gradient = 0 changes in the same direction gradient > 0 changes in opposite directions gradient < 0 EXAMPLES how much will the dependent variable change when the independent variable increases by 1 unit REGRESSION EQUATION SLOPE

Copyright ©2011, Joanna Szyda ERROR error intercept REGRESSION EQUATION

Copyright ©2011, Joanna Szyda small errorlarge error REGRESSION EQUATION ERROR

Copyright ©2011, Joanna Szyda observed value (y) predicted value (ŷ) REGRESSION EQUATION

Copyright ©2011, Joanna Szyda Dependent variableIndependent variable intercept slope REGRESSION EQUATION

Copyright ©2011, Joanna Szyda dependent variableindependent variable intercept slope HOW TO INTERPRET THOSE VALUES ??? REGRESSION EQUATION

ESTIMATION OF REGRESSION COEFFICIENTS

Copyright ©2011, Joanna Szyda LEAST SQUARES HOW TO ESTIMATE REGRESSION COEFFICIENTS ? SO THAT DISTANCES BETWEEN OBSERVED AND PREDICTED VALUES WERE AS SMALL AS POSSIBLE - least squares method

Copyright ©2011, Joanna Szyda  ( ) 2 → minimum LEAST SQUARES

Copyright ©2011, Joanna Szyda LEAST SQUARES

Copyright ©2011, Joanna Szyda LEAST SQUARES

Copyright ©2011, Joanna Szyda WEIGHTING OF OBSERVATIONS WEIGHTED LEAST SQUARES HOW TO ESTIMATE REGRESSION COEFFICIENTS WHEN y ARE MEASURED WITH DIFFERENT ACCURACY?

Copyright ©2011, Joanna Szyda WEIGHTED LEAST SQUARES

EXAMPLES OF REGRESSION EQUATIONS

Copyright ©2011, Joanna Szyda EXAMPLES OF REGRESSION EQUATIONS MULTIPLE REGRESSION BODY WEIGHTAGE ADIPOSE TISSUE

Copyright ©2011, Joanna Szyda POLYNOMIALS 1st grade polynomial 2nd grade polynomial 3rd grade polynomial EXAMPLES OF REGRESSION EQUATIONS

Copyright ©2011, Joanna Szyda LOGHARITMIC REGRESSION EXAMPLES OF REGRESSION EQUATIONS

RESULT INTERPRETATION

Copyright ©2011, Joanna Szyda RESULT INTERPRETATION

Copyright ©2011, Joanna Szyda 1.Time between calls diminishes with temparature rise 2.Temperature increase by 1°C results in call interval shorter by 0.21 s. 3.At 10°C frogs call every 6.26 s. on average: RESULT INTERPRETATION

Copyright ©2011, Joanna Szyda RESULT INTERPRETATION

Copyright ©2011, Joanna Szyda 1.Model: 2.Partners who in 2003 were on average 40 years old and where a husband was 15 years older than his wife, have on average 2.42 children: 3.Partners who in 2003 were on average 25 years old and where a husband was 4 years older than his wife, have on average 2.66 children: RESULT INTERPRETATION

LINEAR REGRESSION