R: Risk Factors for Infection in Caesarian Births

Caesar {vcdExtra} | R Documentation

## Risk Factors for Infection in Caesarian Births

### Description

Data from infection from birth by Caesarian section, classified by `Risk` (two levels), whether `Antibiotics` were used (two levels) and whether the Caesarian section was `Planned` or not. The outcome is `Infection` (three levels).

### Usage

    data(Caesar)

### Format

A 4-dimensional array resulting from cross-tabulating 4 variables for 251 observations. The variable names and their levels are:

No | Name | Levels
1 | `Infection` | `"Type 1", "Type 2", "None"`
2 | `Risk` | `"Yes", "No"` (presence of risk factors)
3 | `Antibiotics` | `"Yes", "No"` (were antibiotics given?)
4 | `Planned` | `"Yes", "No"` (was the C section planned?)

### Details

`Infection` is regarded as the response variable here. There are quite a few 0 cells here, particularly when `Risk` is absent and the Caesarian section was unplanned. Should these be treated as structural or sampling zeros?

### Source

Fahrmeir, L. & Tutz, G. (1994). Multivariate Statistical Modelling Based on Generalized Linear Models New York: Springer Verlag, Table 1.1.

### See Also

`caesar` for the same data recorded as a frequency data frame with other variables.

### Examples

    data(Caesar)
    #display table;  note that there are quite a few 0 cells
    structable(Caesar)
    require(MASS)

    # baseline model, Infection as response
    Caesar.mod0 <- loglm(~Infection + (Risk*Antibiotics*Planned), data=Caesar)
    # NB: Pearson chisq cannot be computed due to the 0 cells
    Caesar.mod0

    mosaic(Caesar.mod0, main="Baseline model")

    # Illustrate handling structural zeros
    zeros <- 0+ (Caesar >0)
    zeros[1,,1,1] <- 1
    structable(zeros)

    # fit model excluding possible structural zeros
    Caesar.mod0s <- loglm(~Infection + (Risk*Antibiotics*Planned), data=Caesar,
    	start=zeros)
    Caesar.mod0s

    anova(Caesar.mod0, Caesar.mod0s, test="Chisq")

    mosaic (Caesar.mod0s)

    # what terms to add?
    add1(Caesar.mod0, ~.^2, test="Chisq")

    # add Association of Infection:Antibiotics
    Caesar.mod1 <- update(Caesar.mod0, ~.+Infection:Antibiotics)
    anova(Caesar.mod0, Caesar.mod1, test="Chisq")

    mosaic(Caesar.mod1, gp=shading_Friendly, main="Adding Infection:Antibiotics")

[Package vcdExtra version 0.7-1 Index]