Component Solution Services REC02F Manual de usuario descargar pdf (Pagina 43)

Tips Recipes Brio 2002

Section Type: Chart section

Tip Name: Best-Fit Charts

Purpose / Use: One typical way to analyze data is to compare the actual data with an

ideal set of values to see how the actual results compare with expected

results. Best-fit charts are a way to display this. Best-fit charts are not a

type available as a choice in the chart toolbar, but they can be easily

created.

Sample File: Scatter plots.bqy

Steps to Produce: Create a scatter chart of the actual data, then add a computed item to

plot the best fit values.

1) Create a line chart, using your actual data points.

Do not change any line properties till after you have added all the fact columns.

Otherwise, the chart engine will reset all facts to the default settings each time a new fact

is added.

2) You will use a linear regression formula to calculate the best-fit plot. A best-fit line will

use the formula y = mx + b, where m=slope and b=y-intercept. To create a computed item

named “Best Fit”, you will need to compute the average slope of the data points and a y-

intercept value.

The slope of a line is defined as (y2-y1) / (x2-x1). In this case, the Length_m column

holds the y-values, and the Mass_kg column holds the x-values. Since the sample values

of y start where x=0, we can use the minimum column value as the y-intercept.

3) In the Results section, create a computed item named “Slope” using a formula similar to

the following:

(Length__m_-Prior(Length__m_))/(Mass__kg_-Prior(Mass__kg_))

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Component Solution Services REC02F Manual de usuario Pagina 43