wtest function

Walter and Elwood's Test of Seasonality

Tests for a seasonal pattern in Binomial data.

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).

Returns

• 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.

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)

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.

Author(s)

Adrian Barnett a.barnett@qut.edu.au