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I have been using 'exact matching' in R to match my treatment group with a control group. My treatment group has 535 cases and the control group has 1892. I would like both groups to be equal and I thought I could achieve this by writing ratio 1. However, the control group has 200 more cases than the controls.

Here is my code:

library(MatchIt)
m.out <- matchit(BA ~ age + gender + income, data=Book2, method="exact", ratio=1)
summary(m.out)

Here is the output:

Sample sizes:
          Control Treated
All          1892     535
Matched       637     466
Discarded    1255      69

Please advise me on how I can get both groups to have 466 cases.

Nottsuni
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    Welcome to Stack Overflow! Please read [**How do I format my code blocks?**](https://meta.stackexchange.com/a/22189/371738) and learn to format your code properly, this time I've helped you. In addition we're only able to reproduce your issue if you'd [**provide some data**](https://stackoverflow.com/questions/5963269/how-to-make-a-great-r-reproducible-example/5963610#5963610), e.g. by adding `dput(Book2)` as an edit to your question. – jay.sf Apr 21 '19 at 10:11
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    Very late to the party but have you looked at mmsample on CRAN? – Gladwell Feb 02 '20 at 09:50

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