patterson.switchback {agridat} | R Documentation

## A switchback trial in dairy cattle

### Description

A switchback trial in dairy cattle

### Usage

    data("patterson.switchback")

### Format

A data frame with 36 observations on the following 4 variables.

`y`

  response, milk FCM

`trt`

  treatment factor, 4 levels

`period`

  period factor, 3 levls

`cow`

  cow factor, 12 levels

### Details

There are three periods. Each cow is assigned to one treatment cycle like T1-T2-T1, where T1 is the treatment in period P1 and P3, and T2 is the treatment in period P2.

There are four treatments.

All 4*3 = 12 treatment cycles are represented.

Data were extracted from Lowry, page 70.

### Source

Patterson, HD and Lucas, HL. 1962. Change-over designs. Technical Bulletin 147, North Carolina Agricultural Experimental Station.

### References

Lowry, S.R. 1989. Statistical design and analysis of dairy nutrition experiments to improve detection of milk response differences. Proceedings of the Conference on Applied Statistics in Agriculture, 1989. http://newprairiepress.org/agstatconference/1989/proceedings/7/

### Examples

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

    # Create groupings for first treatment, second treatment
    datp1 <- subset(dat, period=="P1")
    datp2 <- subset(dat, period=="P2")
    dat$p1trt <- datp1$trt[match(dat$cow, datp1$cow)]
    dat$p2trt <- datp2$trt[match(dat$cow, datp2$cow)]

    if(require(latticeExtra)){
      useOuterStrips(xyplot(y ~ period|p1trt*p2trt, data=dat,
                            group=cow, type=c('l','r'),
                            auto.key=list(columns=5),
                            main="patterson.switchback",
                            xlab="First/Third period treatment",
                            ylab="Second period treatment"))
    }

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

    # Need to use 'terms' to preserve the order of the model terms
    m1 <- aov(terms(y ~ cow + per:cow + period + trt, keep.order=TRUE), data=dat)
    anova(m1) # Match table 2 of Lowry
    ## Analysis of Variance Table
    ##           Df Sum Sq Mean Sq F value    Pr(>F)
    ## cow       11 3466.0 315.091 57.1773 2.258e-06 ***
    ## cow:per   12  953.5  79.455 14.4182 0.0004017 ***
    ## period     1   19.7  19.740  3.5821 0.0950382 .
    ## trt        3   58.3  19.418  3.5237 0.0685092 .
    ## Residuals  8   44.1   5.511

[Package agridat version 1.16 Index]