| qcc.overdispersion.test {qcc} | R Documentation |
This function allows to test for overdispersed data in the binomial and poisson case.
qcc.overdispersion.test(x, size, type=ifelse(missing(size), "poisson", "binomial"))
x |
a vector of observed data values |
size |
for binomial data, a vector of sample sizes |
type |
a character string specifying the distribution for testing, either "poisson" or "binomial". By default, if size is provided a binomial distributed is assumed, otherwise a poisson distribution. |
This very simple test amounts to compute the statistic
| D = Observed variance / Theoretical variance times (no. observations - 1) |
and refer this to a Chi-square distribution with (no. observations - 1) degrees of freedom.
The function returns a matrix of results.
Luca Scrucca luca@stat.unipg.it
Wetherill, G.B. and Brown, D.W. (1991) Statistical Process Control, New York, Chapman and Hall, pp. 216–218
# data from Wetherill and Brown (1991) pp. 212--213, 216--218:
x <- c(12,11,18,11,10,16,9,11,14,15,11,9,10,13,12,
8,12,13,10,12,13,16,12,18,16,10,16,10,12,14)
size <- rep(50, length(x))
qcc.overdispersion.test(x,size)
x <- c(11,8,13,11,13,17,25,23,11,16,9,15,10,16,12,
8,9,15,4,12,12,12,15,17,14,17,12,12,7,16)
qcc.overdispersion.test(x)