I am currently working on a health care related project using R. I am learning R while working on data analysis.
Below is the part of the data in which i am encountering a problem. Case# Sex Therapy1 Therapy2 Outcome 1 male no no Alive 2 female no no Death 3 male no no Alive 4 female no no Death 5 male no no Death 6 male no no Alive 7 male yes no Alive 8 female no no Death 9 male no yes Alive 10 female no no Death 11 female yes yes Death 12 female yes no Death 13 female yes no Death 14 female yes no Alive 15 male yes no Alive 16 male yes no Alive 17 male no yes Death 18 male no yes Death 19 male yes no Alive 20 female no yes Death 21 female yes no Alive 22 female no yes Death 23 male yes no Alive 24 female yes no Alive 25 female yes no Alive "Outcome" is the response variable and "Sex", "Therapy1", "Therapy2" are predictor variables. All of the predictors are significantly associated with the outcome by univariate analysis. Logistic regression runs fine with most of the predictors when "Sex" and "Therapy1" are not included at the same time (This is a part of table that I cut out from a larger table for ease of presentation and there are more predictors that i tested). However, when "Sex" and "Therapy1" are included in logistic regression model at the same time, standard error inflates and p value gets close to 1. The formula used is, >Model<-glm(Outcome~Sex+Therapy1,data=a,family=binomial) #I assigned a vector "a" to represent above table. After doing some reading, I suspect this might be collinearity, as vif values (using "vif()" function in car package) were sky high (8,875,841 for both "Sex" and "Therapy1"). Learning that ridge regression may be a solution, I attempted using logisticRidge {ridge} using the following formula, but i get the accomapnying error message. >logisticRidge(a$Outcome~a$Sex+a$Therapy1) Error in ifelse(y, log(p), log(1 - p)) : invalid to change the storage mode of a factor At this point I do not have an idea how to solve this and would like to seek help. I really really appreciate your input!!! [[alternative HTML version deleted]] ______________________________________________ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.