7-5-12

Graphing Paired-Variable Statistical Data

Drawing a Power Regression Graph ( y = a·xb)

Power regression can be used when y is proportional to the power of x. The normal power regression formula is y = a · xb. If we obtain the logarithms of both sides, we get ln(y) = ln(a)

+b · ln(x). Next, if we say that X = ln(x), Y = ln(y), and A = ln(a), the formula corresponds to the linear regression formula Y = A + b·X.

u ClassPad Operation

Start the graphing operation from the Statistics application’s Graph window or List window.

From the Graph window

Tap [Calc] [Power Reg] [OK] [OK] ".

From the List window

Tap [SetGraph][Setting...], or G.

On the Set StatGraphs dialog box that appears, configure a StatGraph setup with the setting shown below, and then tap [Set].

Type: PowerR

Tap yto draw the graph.

The following is the power regression model formula.

y= a·xb

a : regression coefficient

b : regression power

r : correlation coefficient

r2 : coefficient of determination

MSe : mean square error

 

1

 

n

• MSe =

 

Σ (ln (yi) – (ln (a) + b·ln (xi)))2

n –

2

 

i=1

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