Stata 15 help for mi_noupdate_option

[MI] noupdate option -- The noupdate option

Syntax

mi ... [, ... noupdate ... ]

Description

Many mi commands allow the noupdate option. This entry describes the purpose of that option.

Option

noupdate specifies that the mi command in question need not perform an mi update because you are certain that there are no inconsistencies that need fixing. noupdate is taken as a suggestion; mi update will still be performed if the command sees evidence that it needs to be. Not specifying the option does not mean that an mi update will be performed.

Remarks

Some mi commands perform modifications to the data, and those modifications will go very poorly -- even to the point of corrupting your data -- if certain assumptions about your data are not true. Usually, those assumptions are true, but to be safe, the commands check the assumptions. They do this by calling [MI] mi update. mi update checks the assumptions and, if they are not true, corrects the data so that the assumptions are true. mi update always reports the data corrections it makes.

All of this reflects an abundance of caution, with the result that some commands spend more time running mi update than they spend performing their intended task.

Commands that use mi update to verify assumptions have a noupdate option. When you specify that option, the command skips checking the assumptions, which is to say it skips calling mi update. More correctly, the command skips calling mi update if the command sees no obvious evidence that mi update needs to be called.

You can make commands run faster by specifying noupdate. Should you? Unless you are noticing poor performance, we would say no. It is, however, absolutely safe to specify noupdate if the only commands executed since the last mi update are mi commands. The following would be perfectly safe:

. mi update . mi passive, noupdate: gen agesq = age*age . mi rename age age_at_admission, noupdate . mi ...

The following would be safe, too:

. mi update . mi passive, noupdate: gen agesq = age*age . summarize agesq . mi rename age age_at_admission, noupdate . mi ...

It would be safe because summarize is a reporting command that does not change the data; see [R] summarize.

The problem mi has is that it is not in control of your session and data. Between mi commands, mi does not know what you have done to the data. The following would not be recommended and has the potential to go very poorly:

. mi update . mi passive, noupdate: gen agesq = age*age . drop if female . drop agesq . mi ..., noupdate // do not do this

By the rules for using mi, you should perform an mi update yourself after a drop command, or any other command that changes the data, but it usually does not matter whether you follow that rule because mi will check eventually, when it matters. That is, mi will check if you do not specify the noupdate option.

The noupdate option is recommended for use by programmers in programs that code a sequence of mi commands.


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