Regression & Correlation

• PMCC: product moment correlation coefficient
• r : $-1\ \le r\ \le\ 1$
• What does r measure?

  strength and positivity or negativity of correlation
• Regression line = line of best fit
• What is the typical form of the regression line?

  
  

  $y\ =$$\ a\ +$$\ bx$
• In the regression line what does a represent?

  y when x = 0
• In the regression equation what does b represent?

  how much y changes with x
• extrapolation: estimating outside the data range
• What's more reliable, interpolation or extrapolation?

  interpolation
• If you have a non-linear model, what must you do?

  take logs
• In the case of $y\ =$$\ ab^x$ :

  
  

  $\ln y\ =$$\ \ln a\ +$$\ x\ln b$
• In the case of $y\ =$$\ ax^n$ :

  
  

  $\ln y\ =$$\ \ln a\ +$$\ n\ln x$