1. Presentation, data and programs at:
Stata0, Introduction
Hein Stigum
Presentation, data and programs at:

2. Why Stata Pro Con Aimed at epidemiology Many methods, growing Graphics
Structured, Programmable
Coming soon to a course near you
Con
Memory>file size
Copy tables
Time: 1 h 15 min
Used by leading univ, and at many summer schools
Apr-19
H.S.

3. Data handling

4. Import data Using SPSS 14.0 Save as, Stata Version 8 SE Apr-19 H.S.
New version of DBMSCopy support lonf variable names
Apr-19
H.S.

5. Interface
Apr-19
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6. Do Editor New Run Ctrl-8, or: Mark commands, Ctrl-D to do (execute)
Open do file
Copy commands
Copy review to clipboard
Run commands
Apr-19
H.S.

7. Do-file example
Apr-19
H.S.

8. Syntax Syntax Examples
[bysort varlist:] command [varlist] [if exp] [in range][, opts]
Examples
mean age
mean age if sex==1
bysort sex: summarize age
summarize age ,detail
All commands same
Some simple and some advanced options (and prefixes)
Apr-19
H.S.

9. Use and save data Open data Describe Save data set memory 200m
use “C:\Course\Myfile.dta”, clear
Describe
describe describe all variables
list x1 x2 in 1/20 list obs nr 1 to 20
Save data
save “C:\Course\Myfile.dta” ,replace
Default memory=10m
Have we seen in 1/20 before?
Apr-19
H.S.

10. Drop and keep Drop Keep drop x1 x2 drop variables x1 and x2
drop if sex==1 drop males
drop if age==. drop missing
Keep
same as drop
Drop var =columns
Drop obs =lines
Apr-19
H.S.

11. Recode Syntax From 4 to 2 groups:
recode educ (1 2=1) (3 4=2)(missing=.), gen(educ2)
From cont. to 3 groups:
recode age (min/19=1) (20/29=2) (30/max=3), gen(age3)
Auto: 3 equal sized groups with labels
at() values outside set to missing
String
destring stringvar, generate(newvar) force
force specifies that any string values containing non-numeric characters be treated as indicating missing numeric values.
Apr-19
H.S.

12. Labels Variable Value List label variable q1 ”Age”
1 ) label define freqLab 1”Low” 2”Med” 3”High”
2a) label values smoke freqLab
2b) label values drink freqLab
List
label list
Label list: show all variables with their labels
Names and labels are used in plots: define good english names
May also add information in labels (N=230)
Add numeric coding to labels: numlab, add/remove
Apr-19
H.S.

13. Generate, replace Age square Young/Old Alternatives
generate ageSqr=age^2
Young/Old
generate old=0 if (age<=50)
replace old=1 if (age>50)
Observation numbers
gen id=_n
gen lag=age[ _n-1]
Alternatives
generate old=(age>50)
generate old=(age>50) if age<.
Missing defined in next slide
Apr-19
H.S.

14. Dates From numeric to date From string to date ex: m=12, d=2, y=1987
generate bdate=mdy(m,d,y)
format bdate %d
From string to date
ex: bstr=“ ”
generate bdate=date(bstr,”dmy”)
Apr-19
H.S.

15. Missing Obs!!! Test Remove Change Missing values are large numbers
age>30 will include missing.
age>30 if age<. will not.
Test
replace x=0 if (x==.)
Remove
drop if age==.
Change
replace educ=. if educ==99
gen age2=(age>30) if age!=.
Also .a .b .c …
Apr-19
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16. Describe missing
Summarize variables
Missing in tables
Apr-19
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17. Handle data with many variables
Describe
describe vars format and labels
summarize vars N, mean, std, min and max
codebook vars range, missing, mean and std, percentiles
Find variables
describe, simple list all variables
lookfor age list variables with “age” in name or label
describe age*, n list vars starting with “age” and show var number
Change order
order vars change order of variables
Apr-19
H.S.

18. Help General Examples help command findit keyword search Stata+net
help table
findit aflogit
findit key=search key,all
rc=return code
Apr-19
H.S.

19. Summing up Use do files Syntax Missing Help
Mark, Ctrl-D to do (execute)
Syntax
command [varlist] [if exp] [in range] [, options]
Missing
age>30 & age<.
generate old=(age>50) if age<.
Help
help describe
Apr-19
H.S.

20. Books Data Analysis Using Stata by Ulrich Kohler and Frauke Kreuter
Statistics with Stata (Updated for Version 9) by Lawrence C. Hamilton
A visual guide to Stata graphics by M.N. Mitchell
Multilevel and longitudinal modeling using Stata by S. Rabe-Hesketh, A. Skrondal
Apr-19
H.S.