Stat Computing > Stata > Notes

Stata Class Notes
Let's Get Organized

1.0 Stata commands in this unit

. order
rename
label data
label variable
label define
label values
replace
recode
note:
notes
save, replace

2.0 Demonstration and Explanation

Let's begin by using a new data set, schdat.dta, it looks like this:

id  a1  t1  gender  a2  t2 tgender
 1  95  88     0    94  95    1
 2  63  86     1    61  94    1
 3  87  80     0    81  84    1
 4  79  70     0    79  87    0
 5  68  78     1    63  69    0
 6  64  87     1    82  96    0
 7  86  75     0    69  76    0
 8  81  94     1    93  92    1
 9  89  79     0    90  78    1
10  78  68     1    80  80    1

. use schdat, clear
describe

The describe tells us the names of the variables but doesn't provide much more information. Here's the scoop on the data: a1 and a2 are scores on two assignments, t1 and t2 are the scores on the midterm and final respectively, gender is the gender of the student (1=female and 0=male). The variable tgender is the gender of the teacher and is also scored 1=female and 0=male. None of this is obvious from looking at the data, so let's get organized.

2.1 ordering & renaming

. order id gender tgender a1 a2 t1 t2
rename a1 assign1
rename a2 assign2
rename t1 midterm
rename t2 final
rename gender female
rename tgender tfemale

The order command changes the order of the varibles. The four rename commands change the names of some of the variables to more meaningful ones. This is a good start but we really need to add some labels to make things clear

2.2 Some labels

. label data "Fall 1999 Stat 100 Scores"
label variable female "student gender"
label variable tfemale "teacher gender"
generate totavg = (assign1 + assign2 + midterm + final) / 4
label variable totavg "total score, divided by 4"
describe

The label data command places a label on the whole dataset. The label variable command makes labels that help explain individual variables. The generate command makes total the sum of the assignments and the midterm and final.  Next we need to assign labels to female and tfemale and make a variable with the grade in the class.

2.3 variable labels and recode

Let's make labels showing that female and tfemale are coded 1=female and 0=male.

label define sex 1 "female" 0 "male"
label values female sex
label values tfemale sex
describe
tab1 female tfemale
tab1 female tfemale, nolabel

The label define command creates a definition for the values 0 and 1 called sex. The label values command connects the values defined for sex with the values in female and tfemale.

. generate grade = totavg
recode grade 0/60=0 60/70=1 70/80=2 80/90=3 90/100=4
label define abcdf  0 "F" 1 "D" 2 "C" 3 "B" 4 "A"
label values grade abcdf
list grade totavg

The  generate and recode commands make a new variable grade going from 1 to 5. Using label define and label values the values of grade are labeled A - F.

2.4 Make a note of this

. note: gender is self-report
note: the final was a take-home exam
notes
save schdat2
use schdat2, clear

The note: (note the colon, ":") command allows you to place notes into the dataset. The command notes displays the notes. The save, replace saves the dataset as schdat2.dta.

3.0 Can you answer these questions?

1. Do you think that the variables midterm and final need variable labels?
2. Type summarize. What do the means of female and tfemale mean?
3. What would happen if you did not save your data after recoding and adding labels and notes? Is there any other way to keep track of everything you have done so far?

4.0 For More Information

• Statistics with Stata 5 (recommended text). 
  Chapter (especially pages 16 & 24)
• Stata Learning Modules
  Labeling Data
  Creating and Recoding Variables