Stata 15 help for set fvtrack

Title

[P] set fvtrack -- Keep track of levels for factor variables

Syntax

set fvtrack {term | factor} [, permanently]

Description

set fvtrack allows you to control how Stata keeps track of factor levels when you use factor-variables notation.

contrast behaves as if set fvtrack factor is in effect, regardless of the current setting.

menl behaves as if set fvtrack term is in effect, regardless of the current setting.

Option

permanently specifies that, in addition to making the change right now, the setting be remembered and become the default setting when you invoke Stata.

Remarks

Assume that we have the following factor variables:

Factor ind has 2 levels, taking on the values 0 and 1.

Factor grp has 3 levels, taking on the values 1, 2, and 3.

The expansion of i.ind is

0b.ind 1.ind

The expansion of i.grp is

1b.grp 2.grp 3.grp

The expansion of their interaction i.ind#i.grp is

0b.ind#1b.grp 0b.ind#2.grp 0b.ind#3.grp 1.ind#1b.grp 1.ind#2.grp 1.ind#3.grp

When set fvtrack factor is in effect, or when it is implied by setting version, user to a version less than 15, Stata keeps track of factor levels with the factor variable. This means that specifying a level for grp in one term will affect all other terms that contain grp. For example, the expansion of

i3.grp i.ind#i.grp

is

3.grp 0b.ind#3.grp 1.ind#3.grp

and the expansion of

i.grp i.ind#i3.grp

is

3.grp 0b.ind#3.grp 1.ind#3.grp

When set fvtrack term is in effect, Stata keeps track of factor levels with the term in which they are specified. This means that specifying a level for grp in one term does not affect any other term that contains grp. Using the above examples, we see that the expansion of

i3.grp i.ind#i.grp

is

3.grp 0b.ind#1b.grp 0b.ind#2.grp 0b.ind#3.grp 1.ind#1b.grp 1.ind#2.grp 1.ind#3.grp

and the expansion of

i.grp i.ind#i3.grp

is

1b.grp 2.grp 3.grp 0b.ind#3.grp 1.ind#3.grp


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