retinal {simplexreg}

Data on recorded decay of intraocular gas in complex retinal surgeries

Description

The study recorded the decay of intraocular gas C_3F_8 in complex retinal surgeries following initial injection in an ophthalmology study, reported in Meyers et al. (1992). The outcome variable was the percent of gas left in the eye. The gas, with three different concentration levels, 15%, 20% and 25% was injected into the eye before surgery for 31 patients. They were then followed three to eight (average of five) times over a three-month period, and the volume of gas in the eye at the follow-up times were recorded as a percentage of the initial gas volume. The primary interest was to investigate whether concentration levels of the gas injected in patients' eyes affect the decay rate of the gas.

Usage

data("retinal")

Format

A data frame with 181 observations on the following 6 variables.

Gas

Percentage of the initial gas volume left

Time

Time covariate of days after the gas injection

LogT

Logarithm of Time

LogT2

Square of LogT

Level

Concentration levels of the initial intraocular gas. For each patient, Level = -1 if the gas concentration level is 15%, Level = 0 if 20%, or 1 if 25%.

ID

A factor indicating patients.

References

Meyers, S. M. and Ambler, J. S. and Tan, M. (1992) Variation of Perfluorpropane Disappearance after Vitrectomy. Retinal, 12: 359–363

Zhang, P. and Qiu, Z. and Shi, C. (2016) simplexreg: An R Package for Regression Analysis of Proportional Data Using the Simplex Distribution. Journal of Statistical Software, 71: 1–21