Introduction to Stata 8 - (GRIPS

Numeric formats [U] 15.5.1
The default is General format, presenting values as readable and precisely as possible. In most
cases you need not bother with numeric formats, but you may specify:
format dollars kroner %6.2f
Format Formula Example 2 1,000 10,000,000
General %w.dg %9.0g 1.414214 1000 1.00e+07
Fixed %w.df %9.0f 1 1000 10000000
%9.2f 1.41 1000.00 1.00e+07
Exponential %w.de %10.3e 1.414e+00 1.000e+03 1.000e+07
w: The total width, including period and decimals. d: Number of decimals
You may use comma formats with Stata, but there are confusing limitations, and I don't
recommend it. To display commas rather than periods (probably most relevant for graphs):
set dp comma
6.3. Missing values [U] 15.2.1
Missing values are omitted from calculations. There are two types of missing values:
The system missing value is shown as a . (period). It is created in input when a numeric field
is empty; by invalid calculations, e.g. division by 0, or calculations involving a missing value.
User-defined missing values are .a, .b, .c, ... .z . It is a good idea to use a general
principle consistently, e.g.:
.a Question not asked (complications to an operation not performed)
.b Question asked, no response
.c Response: Don't know
Unfortunately no data entry program accepts .a in a numeric field. In EpiData you might
choose the codes -1 to -3 (provided, of course, that they could not be valid codes) and let
Stata recode them:
recode _all (-1=.a)(-2=.b)(-3=.c)
Missing values are high-end numbers; the ordering is:
All valid numbers < . < .a < .b < ... < .z
You need not bother about the actual numerical values behind the missing values, but you
need to know the logics to avoid mistakes. In calculations missing values behave as expected,
but not so in conditions. The following command initially surprised me by listing all whose
age was > 65, and those with missing age:
list age if age > 65
To exclude the missing:
list age if age > 65 & age < .
To list the missing only, including the user-defined missing values:
list id age if age >= .
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