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SPSS® 12.0 Command Syntax Reference

SPSS® 12.0 Command Syntax Reference

SPSS® 12.0 Command Syntax Reference

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IGRAPH 763<br />

REGRESSION Fits a straight line (or surface) using ordinary least squares. Must be followed<br />

by the keyword LINEAR.<br />

ORIGIN Fits a straight line (or surface) through the origin. Must be followed by the<br />

keyword LINEAR.<br />

MEAN For a 2-D chart, fits a line at the mean of the dependent (Y) variable. For a<br />

3-D chart, the Y mean is shown as a plane.<br />

LLR Fits a local linear regression curve or surface. A normal (NORMAL) kernel<br />

is the default. With EPANECHNIKOV, the curve is not as smooth as with a normal<br />

kernel and is smoother than with a uniform (UNIFORM) kernel. (For<br />

more information, see Simonoff, J. S. 1966. Smoothing methods in statistics.<br />

New York: Springer-Verlag.)<br />

The keyword LINE indicates the number of fit lines. TOTAL fits the line to all of the cases.<br />

MEFFECT fits a separate line to the data for each value of a legend variable.<br />

The REGRESSION, ORIGIN, and MEAN methods offer the option of including prediction<br />

intervals with the following keyword:<br />

INTERVAL[(cval)] The intervals are based on the mean (MEAN) or on the individual cases<br />

(INDIVIDUAL). Cval indicates the size of the interval and ranges from<br />

50 to 100.<br />

The local linear regression (LLR) smoother offers the following controls for the smoothing<br />

process:<br />

BANDWIDTH Constrains the bandwidth to be constant across subgroups or panels<br />

(CONSTRAINED). The default is unconstrained (FAST).<br />

X1MULTIPLIER Specifies the bandwidth multiplier for the X1 axis. The bandwidth<br />

multiplier changes the amount of data that is included in each calculation<br />

of a small part of the smoother. The multiplier can be adjusted to<br />

emphasize specific features of the plot that are of interest. Any positive<br />

multiplier (including fractions) is allowed. The larger the multiplier,<br />

the smoother the curve. The range between 0 and 10 should<br />

suffice in most applications.<br />

X2MULTIPLIER Specifies the bandwidth multiplier for the X2 axis. The bandwidth<br />

multiplier changes the amount of data that is included in each calculation<br />

of a small part of the smoother. The multiplier can be adjusted to<br />

emphasize specific features of the plot that are of interest. Any positive<br />

multiplier (including fractions) is allowed. The larger the multiplier,<br />

the smoother the curve. The range between 0 and 10 should<br />

suffice in most applications.

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