try removing quotes "" around my.dat i.e. data=my.dat Sent from my StrawBerry® On 09/mar/2013, at 17:58, "Ruhil, Anirudh" &lt;ruhil(a)ohio.edu&gt; wrote: > Hello All; > > I am trying to get a situation of matching for multiple treatments resolved via cem but ran into an error message with my data. I then switched to a randomly generated data frame (see below) but still get the error message. Any clues as to the culprit? > >> set.seed(03092013) >> a <- as.factor(c(rep(1,35),rep(2,35), rep(3,30))) >> b <- runif(100, min=0, max=100) > >> my.dat <- data.frame(a, b) > >> mat <- cem(treatment="a", data="my.dat") > Error: Data must be a data frame > >> class(my.dat) > [1] "data.frame" >> str(my.dat) > 'data.frame': 100 obs. of 2 variables: > $ a: Factor w/ 3 levels "1","2","3": 1 1 1 1 1 1 1 1 1 1 ... > $ b: num 20.4 16.7 87 81.1 87.9 ... > > many thanks in advance!! > > Ani > > > > - > -- > cem Mailing List, served by HUIT > Send messages: cem(a)lists.gking.harvard.edu > [un]subscribe Options: http://lists.gking.harvard.edu/?info=cem > More information on cem: http://gking.harvard.edu/cem > Cem mailing list > Cem(a)lists.gking.harvard.edu > > To unsubscribe from this list or get other information: > > https://lists.gking.harvard.edu/mailman/listinfo/cem