Line Plot

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Fitted Line Plot


Purpose

The Fitted Line Plot is used to graphically represent the relationship between a continuous dependent variable (Y) and an continuous independent variable (X), for a process operating in its natural state.


Anatomy

line plot

Reference: Minitab Reference Manual

Terminology

A. Fitted Line through the data. The regression line is simply the one that best fits the plotted data, and relates the independent variable (X) to our dependent variable (Y) (see tool Linear Regression).

B. Confidence bands about the fitted regression line at a specified confidence level, (usually 95% level). In other words, we are 95% confident that the plotted data falls within these two lines.

C. Prediction bands about the fitted regression line at the confidence level specified, (usually 95% level). In other words, we are 95% confident that the fitted regression line “A” falls within these two lines.

D. Regression Equation - A prediction equation, which allows the values of the inputs to predict a corresponding output.

E. Coefficient of Determination: r2, is a number that represents the adequacy of the regression model or the amount of the variation in Y that can be explained by the regression equation.


Major Considerations

This tool should be used after finding a satisfactory model through regression analysis.

Application Cookbook

1. Carry out regression analysis.

2. Analyze data with Minitab:

  • Use the Function under Stat > Regression > Fitted Line Plot.
  • Input the name of the dependent variable into the ‘Response’ field, and the name of the independent variable into the ‘Predictor’ field.
  • Go to options and select ‘Display confidence bands’ and ‘Display prediction bands’.

From Fitted Line Plot to Six Sigma Tools.

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