Stata 15 help for indepvars

Title

[U] 11.4 varname and varlists

Description

A varlist is a list of variable names. The variable names in a varlist refer either exclusively to new (not yet created) variables or exclusively to existing variables. A newvarlist always refers exclusively to new (not yet created) variables. Similarly, a varname refers to one variable, either existing or not yet created. A newvar always refers to one new variable.

Sometimes a command will refer to a varname in another way, such as "groupvar". This is still a varname. The different name is used to give you an extra hint about the purpose of that variable. For example, a groupvar is the name of a variable that defines groups within your data. Other common ways of referring to a varname or varlist in Stata are

depvar, which means the dependent variable for an estimation command;

indepvars, which means a varlist containing the independent variables for an estimation command;

xvar, which means a continuous real variable, often plotted on the x axis of a graph;

yvar, which means a variable that is a function of an xvar, often plotted on the y axis of a graph;

clustvar, which means a numeric variable that identifies the cluster or group to which an observation belongs;

panelvar, which means a numeric variable that identifies panels in panel data, also known as cross-sectional time-series data; and

timevar, which means a numeric variable with a %td, %tc, or %tC format.

Examples include

myvar just one variable myvar thisvar thatvar three variables myvar* variables starting with myvar *var variables ending with var my*var variables starting with my & ending with var with any number of other characters between my~var one variable starting with my & ending with var with any number of other characters between my?var variables starting with my & ending with var with one other character between myvar1-myvar6 myvar1, myvar2, ..., myvar6 (probably) this-that variables this through that, inclusive

The * character indicates to match one or more characters. All variables matching the pattern are returned.

The ~ character also indicates to match one or more characters, but unlike *, only one variable is allowed to match. If more than one variable matches, an error message is presented.

The ? character matches one character. All variables matching the pattern are returned.

The - character indicates that all variables in the dataset, starting with the variable to the left of the - and ending with the variable to the right of the - are to be returned.

Many commands understand the keyword _all to mean all variables. Some commands default to using all variables if none are specified.

Factor variables are extensions of varlists of existing variables. When a command allows factor variables, in addition to typing variable names from your data, you can type factor variables using factor-variable operators.

Factor variables create indicator variables from categorical variables, interactions of indicators of categorical variables, interactions of categorical and continuous variables, and interactions of continuous variables (polynomials).

There are five factor-variable operators:

Operator Description -------------------------------------------------------------------- i. unary operator to specify indicators c. unary operator to treat as continuous o. unary operator to omit a variable or indicator # binary operator to specify interactions ## binary operator to specify factorial interactions --------------------------------------------------------------------

For complete syntax and usage of factor variables, see fvvarlist.

Time-series varlists are a variation on varlists of existing variables. When a command allows a time-series varlist, you may include time-series operators. For instance, L.gnp refers to the lagged value of variable gnp. The time-series operators are

Operator Meaning --------------------------------------------------------- L. lag (x_t-1) L2. 2-period lag (x_t-2) ... F. lead (x_t+1) F2. 2-period lead (x_t+2) ... D. difference (x_t - x_t-1) D2. difference of difference (x_t - 2x_t-1 + x_t-2) ... S. "seasonal" difference (x_t - x_t-1) S2. lag-2 (seasonal) difference (x_t - x_t-2) ... ---------------------------------------------------------

Time-series operators may be repeated and combined and both lowercase and uppercase letters are understood. For more details, see help tsvarlist.

Examples

. webuse census4 . describe

These four regress commands are equivalent. . regress brate medage medagesq reg2 reg3 reg4 . regress brate medage medagesq reg2-reg4 . regress brate med* reg2-reg4 . regress brate medage c.medage#c.medage i.region

. summarize _all

. sysuse citytemp . describe

. summarize *dd . summarize temp* . summarize temp??? . summarize t*n

. webuse fvex . describe

. regress y distance i.group . regress y i.sex sex#c.distance

These two commands are equivalent. . regress y distance i.sex i.group sex#group . regress y distance sex##group


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