How to use MatchIt in R when you already have a propensity score?

Question

I have dataset with the following variables:

1. y = continuous outcome variable (would like to known the difference between in outcome between groups 1 and 2)
2. group = 1 or 2 (would like to find matched subsample of the two groups so I can compute the causal difference between them)
3. score = each customer has a score; I would like to match customers based on this score.

Basically I already have the propensity score, and would like to use matchit to do the matching based on score and find weights. What other options are there for distance? I know the default is distance = "logit" but I can't find a list of other options. I'm looking for something like the identity option that allows me to match on score.

matchit(group ~ score, data, method = "full", distance = "logit")

Answer 1

You can simply supply the score variable to the distance argument to use it as the matching variable, i.e.,

matchit(group ~ score, data, method = "full", distance = score)

Note that the variables to the right of the ~ in the formula won't play a role in the matching in this way but will be present for balance checking if you use plot or summary on the output.