How to create a factor variable in regression?
There are at least two ways to create the group variable. The first way is Another, a simpler, way is to use the gl () function: Briefly, gl (n,k) creates a factor vector with n levels and each level has k replications. By default, the levels are labeled ‘1’, ‘2’, …, ‘n’ but it can be changed by setting the labels parameter.
When to remove a level from a factor variable?
(The level is not automatically removed if there are no elements in it because we could just by chance have a sample which did not contain elements from a specific level.) Let’s illustrate this by removing the level of “very.high” from the ses.f variable.
What happens when LM encounters a factor variable?
When lm () encounters a factor variable with two levels, it creates a new variable based on the second level. In our example, the second level is female, and genderfemale is created. It is a binary variable that takes the value 1 if the value of ‘gender’ is female, and 0 if the value of ‘gender’ is not female.
How to create factor variables based on SES?
Creating a factor variable ses.f.bad.order based on ses. The problem is that the levels are ordered according to the alphabetical order of the categories of ses. Thus, “high” is the lowest level of ses.f.bad.order , “middle” is the middle level and “low” is the highest level.
Which is the second variable in diff Statalist?
The second variable is the before vs after variable, which in this situation would be 0 in years before 2004 and 1 in years after. The interaction term you want is then the product of these. The before-after variable is your d04 variable.
How is genderfemale used as a factor variable?
We see that in addition to the intercept and slope for ‘drinks’, there is a third variable ‘genderfemale’. When lm () encounters a factor variable with two levels, it creates a new variable based on the second level. In our example, the second level is female, and genderfemale is created.