Ddiabetic retinopathy

Description

Partial results from a trial of laser coagulation for the treatment of diabetic retinopathy.

Usage

data("diabetic")

Format

A data frame with 394 observations on the following 8 variables.

id

subject id

laser

laser type: xenon or argon

age

age at diagnosis

eye

a factor with levels of left right

trt

treatment: 0 = no treatment, 1= laser

risk

risk group of 6-12

time

time to event or last follow-up

status

status of 0= censored or 1 = visual loss

Details

The 197 patients in this dataset were a 50% random sample of the patients with "high-risk" diabetic retinopathy as defined by the Diabetic Retinopathy Study (DRS). Each patient had one eye randomized to laser treatment and the other eye received no treatment. For each eye, the event of interest was the time from initiation of treatment to the time when visual acuity dropped below 5/200 two visits in a row. Thus there is a built-in lag time of approximately 6 months (visits were every 3 months). Survival times in this dataset are therefore the actual time to blindness in months, minus the minimum possible time to event (6.5 months). Censoring was caused by death, dropout, or end of the study.

References

Huster, Brookmeyer and Self, Biometrics, 1989.

American Journal of Ophthalmology, 1976, 81:4, pp 383-396

Examples

# juvenile diabetes is defined as and age less than 20
juvenile <- 1*(diabetic$age < 20)
coxph(Surv(time, status) ~ trt + juvenile + cluster(id),
            data= diabetic)