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Walter and Elwood's Test of Seasonality

Source: R/wtest.R
wtest.Rd

Tests for a seasonal pattern in Binomial data. A test of whether monthly data has a sinusoidal seasonal pattern. The test has low power compared with the cosinor() test.

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

a list with the following elements:

  • test: test statistic.

  • pvalue: p-value.

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. doi:10.1007/978-3-642-10748-1

Author

Adrian Barnett a.barnett@qut.edu.au

Examples


# 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
)