optimal method with exact matching on some variables

[jiweihe1223]

I used the method = “exact” option to force exact matching on some variables and used other methods for the other variables.

The method = “nearest” approach worked as expected. However, when I tried switching the argument to method = “optimal”, it seems the matching id output by match.matrix do not show the expected matching for the variables specified in the exact option. Why is it so?

You can see in the output, subject 2 and subject 25 who are matched do not have the same age.

Code I used:
match= matchit(A ~ SEX + AGE + V1 + V2, method = "optimal",
exact = c("SEX", "AGE"), data = data_test)
match_id<-match$match.matrix
N<-9
match_id2<-c(1:N, match_id)

match_data<-match.data(match)
#reorder matched control in the same order as treated
match_data2<-match_data[match_id2, ]
match_data2$match_id<-rep(1:N, 2)

Output:

match_data2
SEX AGE V1 V2 A distance weights subclass match_id
1 F 8 5.4 6.0 1 0.19925382 1 1 1
2 F 9 5.7 2.6 1 0.52655669 1 2 2
3 M 10 5.6 1.6 1 0.25929894 1 3 3
4 F 8 5.1 3.7 1 0.19159122 1 4 4
5 M 8 4.6 2.9 1 0.03403255 1 5 5
6 M 7 5.7 4.9 1 0.30804933 1 6 6
7 F 7 5.2 5.2 1 0.21183573 1 7 7
8 F 6 5.3 5.6 1 0.30090303 1 8 8
9 F 6 4.4 4.2 1 0.06211456 1 9 9
30 M 8 5.4 4.1 0 0.15866640 1 1 1
25 F 8 5.4 2.7 0 0.41199904 1 2 2
13 F 6 5.0 3.7 0 0.26556803 1 3 3
28 M 8 5.4 3.9 0 0.16722246 1 4 4
53 F 6 4.3 5.6 0 0.03196558 1 5 5
24 M 7 5.7 4.9 0 0.30804933 1 6 6
51 M 8 5.5 3.4 0 0.23293292 1 7 7
36 F 8 5.2 2.8 0 0.28892715 1 8 8
47 F 6 4.3 3.5 0 0.05998461 1 9 9

[ngreifer]

I'm looking into this. Could you provide the full dataset so I can investigate? On the datasets I have It seems to be working correctly. When you run summary(match), is the Std. Pair Diff. value for AGE different from 0?

[jiweihe1223]

Thanks so much! I attached the dataset. I did not find the Std. Pair Diff. in the summary you mentioned. Please let me know.

…

On Fri, Feb 26, 2021 at 3:31 PM Noah Greifer ***@***.***> wrote: I'm looking into this. Could you provide the full dataset so I can investigate? On the datasets I have It seems to be working correctly. When you run summary(match), is the Std. Pair Diff. value for AGE different from 0? — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <#60 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AS733LGC2AYXXVQX4WUROE3TBAAIZANCNFSM4YHRI6NQ> .

[ngreifer]

Sorry, I don't see the dataset anywhere.

[jiweihe1223]

I attached it in the email reply. Let me try to attach here.
data_test.xlsx

[ngreifer]

Thank you for sending the dataset. It seems like you're using an old version of MatchIt. I was able to replicate your results using version 3.0.2, but not using version 4.0.0 or above. In recent versions, the units are correctly matched. Please update MatchIt and this should be fixed.

Please make sure you are always using the most updated version of a package. In the future, if you think you have found a bug or unexpected behavior, it may have already been fixed in an updated version, saving you and the maintainers time.

[jiweihe1223]

I see. I reinstalled Matchit(). It did solve the problem. Thank you so much! Lesson learned.

…

On Fri, Feb 26, 2021 at 10:07 PM Noah Greifer ***@***.***> wrote: Thank you for sending the dataset. It seems like you're using an old version of MatchIt. I was able to replicate your results using version 3.0.2, but not using version 4.0.0 or above. In recent versions, the units are correctly matched. Please update MatchIt and this should be fixed. Please make sure you are always using the most updated version of a package. In the future, if you think you have found a bug or unexpected behavior, it may have already been fixed in an updated version, saving you and the maintainers time. — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <#60 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AS733LD4TP6UXGXIL3S6WD3TBBOYNANCNFSM4YHRI6NQ> .