10. BEST_FIT (BEST_FIT.WQ1)
==========================

BEST_FIT is a macro library that calculates and plots the best
fit (trend) line for a regression analysis.  A regression
analysis is used to study the correlation between two variables
to determine if a relationship exists.  BEST_FIT will plot your
trend line and independent and dependent variables on an
XY graph.

                      REGRESSION TERMINOLOGY

Ind. Variable  The data that affects the dependent variable.
               (Ex. Number of sales advertisements mailed.)

Dep. Variable  The data that is affected by the independent
               variable.  (Ex. Sales generated by the
               advertisement.)

Constant       The Y intercept of the regression.  This the
               point where the line meets the Y axis.

Std Err / Y Est
               The estimated deviation of the regression line.

R Squared      Measures the validity of the model.  Ranges from
               0 to 1 with 1 being optimal.  It is used as an
               index to compare
               different models with the same number of
               independent variables.

Deg. of Freedom
               The parameter that determines the shape of the
               curve.

X Coefficients The coefficient of the independent variable.  It
               is the slope of the best fit line.

Std Err of Coef
               Gives an error estimate of the
               coefficients.


                           THE FORMULA

The formula Quattro Pro uses to calculate the best fit line is
          _           _
     y' = y + b(x - x)

x = The independent variables
_
x = The average of the independent variables

y = The dependent variables

y'= The Y axis values for the best fit line
_
y = The average of the dependent variables

b = The slope of the best fit line, computed using

            _
          E(x - x)y
     B = 
            _
                 2
          (x - x)


                         TO USE BEST_FIT

   1.  Retrieve the spreadsheet BEST_FIT.WQ1 which contains the
       best fit
       macro.

   2.  Open the spreadsheet containing the data for analysis.

   3.  This macro requires a blank area of your spreadsheet to
       display the regression data.  This area must be at least
       7 columns wide and as many rows as there are points in the
       analysis.  The upper left cell of this block must be named
       R_OUTPUT.  Use /Edit | Names | Create to name this cell.
       Be sure no data appears in this area as it may be erased.

   4.  Press [Alt-A] to execute the macro.

   5.  You will be prompted for the range of your independent and
       dependent variables.

   6.  Quattro Pro will now perform the regression analysis.

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