strate() calculates incidence rates and Corresponding 95\
strate(data, time, status, ..., fail = NULL, per = 1, plot = TRUE, rnd = 3)Dataset
person-time variable
outcome variable: preferrably 1 for event, 0 for censored
Variable or multiple variables
Colon separator : can be used to specify multiple variables.
Specify failure event
units to be used in reported rates
logical value to display plots of rates across a categorical variable
Rounding of numbers
Rates of event occurrences, known as incidence rates are outcome measures in longitudinal studies. In most longitudinal studies, follow-up times vary due to logistic resasons, different periods of recruitment, delay enrolment into the study, lost-to-follow-up, immigration or emigration and death.
Follow-up time in longitudinal studies
Period of observation (called as follow-up time) starts when individuals join
the study and ends when they either have an outcome of interest, are lost-to-
follow-up or the follow-up period ends, whichever happens first. This period is
called person-year-at-risk. This is denoted by PY in strate
function's output and numer of event by D.
Rate
is calcluated using the following formula: $$\lambda = D / PY$$
Confidence interval of rate
is derived using the following formula:
$$95\% CI (rate) = rate x Error Factor$$ $$Error Factor (rate) = exp(1.96 / \sqrt{D})$$
plot, if TRUE, produces a graph of the rates against
the numerical code used for categories of by.
Betty R. Kirkwood, Jonathan A.C. Sterne (2006, ISBN:978<U+2013>0<U+2013>86542<U+2013>871<U+2013>3)