Pixel {nlme} | R Documentation

## X-ray pixel intensities over time

### Description

The `Pixel` data frame has 102 rows and 4 columns of data on the pixel intensities of CT scans of dogs over time

### Format

This data frame contains the following columns:

Dog
  a factor with levels `1` to `10` designating the dog on which the scan was made
Side
  a factor with levels `L` and `R` designating the side of the dog being scanned
day
  a numeric vector giving the day post injection of the contrast on which the scan was made
pixel
  a numeric vector of pixel intensities

### Source

Pinheiro, J. C. and Bates, D. M. (2000) Mixed-effects Models in S and S-PLUS, Springer.

### Examples

    data(Pixel)
    fm1 <- lme(pixel ~ day + I(day^2), data = Pixel,
               random = list(Dog = ~ day, Side = ~ 1))
    summary(fm1)
    VarCorr(fm1)

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