season (version 0.2-6)

wtest: Walter and Elwood's test of seasonality

Description

Tests for a seasonal pattern in Binomial data.

Usage

wtest(cases,offset,data,alpha=0.05)

Arguments

cases

variable name for cases (successes).

offset

variable name for at-risk population (trials).

data

data frame (optional).

alpha

significance level (default=0.05).

Value

• test
  test statistic.
• pvalue
  p-value.

Details

A test of whether monthly data has a sinusoidal seasonal pattern. The test has low power compared with the cosinor test.

References

Walter, S.D., Elwood, J.M. (1975) A test for seasonality of events with a variable population at risk. British Journal of Preventive and Social Medicine 29, 18--21. Barnett, A.G., Dobson, A.J. (2010) Analysing Seasonal Health Data. Springer.

Examples

data(stillbirth)
# tabulate the total number of births and the number of stillbirths
freqs<-table(stillbirth$month,stillbirth$stillborn)
data<-list()
data$trials<-as.numeric(freqs[,1]+freqs[,2])
data$success<-as.numeric(freqs[,2])
# test for a seasonal pattern in stillbirth
test<-wtest(cases=success,offset=trials,data=data)