lucas.switchback {agridat} | R Documentation

## Switchback trial in dairy with three treatments

### Description

Switchback trial in dairy with three treatments

### Usage

    data("lucas.switchback")

### Format

A data frame with 36 observations on the following 5 variables.

`cow`

  cow factor, 12 levels

`trt`

  treatment factor, 3 levels

`period`

  period factor, 3 levels

`yield`

  yield (FCM = fat corrected milk), pounds/day

`block`

  block factor

### Details

Lucas says "because no data from feeding trials employing the present designs are yet available, uniformity data will be used".

Six cows were started together in block 1, then three cows in block 2 and three cows in block 3.

### Source

Lucas, HL. 1956. Switchback trials for more than two treatments. Journal of Dairy Science, 39, 146-154. http://doi.org/10.3168/jds.S0022-0302(56)94721-X

### References

Sanders, WL and Gaynor, PJ. 1987. Analysis of Switchback Data Using Statistical Analysis System. Journal of Dairy Science, 70, 2186-2191. http://doi.org/10.3168/jds.S0022-0302(87)80273-4

### Examples

    data(lucas.switchback)
    dat <- lucas.switchback

    # Create a numeric period variable
    dat$per <- as.numeric(substring(dat$period,2))

    require(lattice)
    xyplot(yield ~ period|block, data=dat, group=cow, type=c('l','r'),
           auto.key=list(columns=6),
           main="lucas.switchback - (actually uniformity data)")

    # Need to use 'terms' to preserve the order of the model terms
    # Really, cow(block), per:cow(block), period(block)
    m1 <- aov(terms(yield ~ block + cow:block + per:cow:block +
                    period:block + trt, keep.order=TRUE), data=dat)
    anova(m1) # Match Sanders & Gaynor table 3
    ## Analysis of Variance Table
    ##               Df  Sum Sq Mean Sq F value    Pr(>F)
    ## block          2   30.93  15.464  55.345 5.132e-05 ***
    ## block:cow      9 1700.97 188.997 676.426 1.907e-09 ***
    ## block:cow:per 12  120.47  10.040  35.932 4.137e-05 ***
    ## block:period   3   14.85   4.950  17.717  0.001194 **
    ## trt            2    1.58   0.789   2.825  0.126048
    ## Residuals      7    1.96   0.279

    coef(m1) # trtT2 and trtT3 match Sanders table 3 trt diffs

[Package agridat version 1.16 Index]