'strata(match.id)' is not a factor warning message

[bethatkinson]

I need to get some attributable risk estimates in R, and am getting a warning that I don’t understand. I don’t get the warning if I run it without the baseline statement, so it must have something to do with that piece. Is this a warning I can ignore, or is there something I need to fix here? Thanks!

Jill

temp25 <-attribrisk(hf~expos(htn)+cad+arr+lip+str+art+ast+can+ckd+cpd+dem+dep+dia+ost+szo+sub+anx+strata(match.id), data=all, baseline=b25)
Warning message:
In model.frame.default(tform, data = baseline, xlev = xlevels, na.action = function(x) x) :
variable 'strata(match.id)' is not a factor
is.factor(all$match.id)
[1] TRUE
is.factor(b25$match.id)
[1] TRUE
temp25
Call:
attribrisk(formula = hf ~ expos(htn) + cad + arr + lip + str +
art + ast + can + ckd + cpd + dem + dep + dia + ost + szo +
sub + anx + strata(match.id), data = all, baseline = b25)

n = 5286
coefficient std. err lower 0.95 upper 0.95
attributable risk 0.07230469 0.01372904 0.09921312 0.04539626