Inverse probability weighting

I'm using the twang package.

When I try to create the survival function:

fitw <- prodlim(Hist(followup, om)~treatment, caseweights=matchcn$w.ATE, data=matchcn)

the following message comes:

Error in prodlim(Hist(followup, om) ~ treatment, caseweights = matchcn$w.ATE, :

The length of caseweights is: 639

this is not the same as the number of subjects with no missing values, which is 599

Can anyone help me?

Thank you in advance,


It sounds like you have missing values in your dataset, matchcn. I don't know the twang package, but you probably need to subset your data to exclude cases where there is an NA value for the subject. There are lots of ways to do this in R, see answers in the Stack Overflow thread below:

Dear Mara,

Thank you for your kind answer.

Unfortunately, I can't use the na.omit function because it would delete the majority of my data.

I tried to search a package for the pair-wise dealing with missing data, but I couldn't find one. Could you recommend a package for me?

What's intersting is that if I do the analyses before the weighting, NA are treated as NA. Then that message comes.

I'm afraid I'm a little out of my depth in terms of what you're asking. If you could make a reprex, it would go a long way towards helping others help you:

A self-contained reprex (short for reproducible example) means that others can reproduce exactly what you're seeing.


If you've never heard of a reprex before, you might want to start by reading the help page. The reprex dos and don'ts are also useful.

There's also a nice FAQ on how to do a minimal reprex for beginners, below:

What to do if you run into clipboard problems

If you run into problems with access to your clipboard, you can specify an outfile for the reprex, and then copy and paste the contents into the forum.

reprex::reprex(input = "fruits_stringdist.R", outfile = "")

For pointers specific to the community site, check out the reprex FAQ.

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