wtest {season}

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).

Details

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

Value

test

test statistic.

pvalue

p-value.

Author(s)

Adrian Barnett [e-mail]

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)