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From |
"louis boakye-yiadom" <louisby@hotmail.com> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: the -missing- command |

Date |
Tue, 11 Oct 2005 12:02:50 +0000 |

Thanks, Jeff and Michael, for the very helpful replies. Louis

From: jpitblado@stata.com (Jeff Pitblado, StataCorp LP)

louis boakye-yiadom <louisby@hotmail.com> asks about the -missing()- function:

> I have two questions regarding the -missing- command (or function?).

> First question:

> I'm not clear about exactly what -missing- does. An example will clarify my

> concern. I have a dataset containing 11 variables (the first is -clust- and

> the last is -s11aq13-). One of the variables is -trexpcd-, and the total

> number of observations is 4872. I gave the following commands and had the

> shown output:

> count if mi(trexpcd)

> 4649

> count if mi(clust-s11aq13)

> 82

> My understanding of the online -help- is that -missing- evaluates the number

> of observations for which any of the arguments is missing. So, for the

> second command, since -trexpcd- is one of the arguments, I expected the

> result to be a number which is at least equal to 4649.

> Can anyone please show me what I'm missing?

> Second question:

> Also, I had the following result:

> count if !mi(clust-s11aq13)

> 4790

> Does !mi() evaluate the number of observations for which none of the

> arguments is missing? Thank you.

I believe what Louis wants is Nick Cox's -nmissing- command, which (among

other things) reports the number of missing values found in the variable of

the dataset:

. ssc install nmissing

(output omitted)

. sysuse auto

(1978 Automobile Data)

. nmissing

rep78 5

.

There is also a companion command called -npresent- that reports the number of

non-missing values found in each variable of the dataset:

. npresent

make 74

price 74

mpg 74

rep78 69

headroom 74

trunk 74

weight 74

length 74

turn 74

displacement 74

gear_ratio 74

foreign 74

Also, look into the -mark- and -markout- commands. They help you generate a

variable that indicates observations that are free of missing values for a

specified list of variables:

. mark touse

. markout touse price-foreign

. count if touse

69

Svend Juul <SJ@SOCI.AU.DK> also replied and was puzzled by the results of the

following commands:

. count if missing(rep78-headroom)

5

. count if missing(mpg-headroom)

0

-missing()- is a function, in this context "rep78-headroom" is interpreted

to mean the difference between the variables -rep78- and -headroom-.

--Jeff

jpitblado@stata.com

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**References**:**Re: st: the -missing- command***From:*jpitblado@stata.com (Jeff Pitblado, StataCorp LP)

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