ChickWeight {nls} | R Documentation

## Weight versus age of chicks on different diets

### Description

The `ChickWeight` data frame has 578 rows and 4 columns from an experiment on the effect of diet on early growth of chicks.

### Usage

    data(ChickWeight)

### Format

This data frame contains the following columns:

weight
  a numeric vector giving the body weight of the chick (gm).
Time
  a numeric vector giving the number of days since birth when the measurement was made.
Chick
  an ordered factor with levels `18` < ...{} < `48` giving a unique identifier for the chick. The ordering of the levels groups chicks on the same diet together and orders them according to their final weight (lightest to heaviest) within diet.
Diet
  a factor with levels 1,...{},4 indicating which experimental diet the chick received.

### Details

The body weights of the chicks were measured at birth and every second day thereafter until day 20. They were also measured on day 21. There were four groups on chicks on different protein diets.

### Source

Crowder, M. and Hand, D. (1990), Analysis of Repeated Measures, {Chapman and Hall} (example 5.3)

Hand, D. and Crowder, M. (1996), Practical Longitudinal Data Analysis, Chapman and Hall (table A.2)

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

### Examples

    data(ChickWeight)
    coplot(weight ~ Time | Chick, data = ChickWeight,
        type = "b", show = FALSE)
    ## fit a representative chick
    fm1 <- nls(weight ~ SSlogis( Time, Asym, xmid, scal ),
        data = ChickWeight, subset = Chick == 1)
    summary( fm1 )

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