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INTRODUCTION TO STATA. Võ Tuấn Khoa Trần Thế Trung. Stata basics. command-driven or menu-driven software modeling complex data from longitudinal studies or surveys deal for analyzing results from clinical trials or epidemiological studies provides a powerful programming language.
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INTRODUCTION TO STATA Võ Tuấn Khoa Trần Thế Trung
Stata basics • command-driven or menu-driven software • modeling complex data from longitudinal studies or surveys deal for analyzing results from clinical trials or epidemiological studies • provides a powerful programming language
Stata command The basic language syntax for STATA commands is [by varlist:] command [varlist] [=exp] [if exp] [in range] [weight] [using filename] [, options] where the elements between brackets are optional.
Stata command • [by varlist:] instructs Stata to repeat the command for each combination of values in the list of variables varlist. • [command] is the name of the command and can be abbreviated; for example, the command display can be abbreviated as dis. • [varlist] is the list of variables to which the command applies. • [=exp] is an expression. • [if exp] restricts the command to that subset of the observations that satisfies the logical expression exp. • [in range] restricts the command to those observations whose indices lie in a particular range. • [weight] allows weights to be associated with observations • [using filename] specifies the filename to be used. • [options] are specific to the command and may be abbreviated.
Stata command • Example 1 • Stata Command: .bysort black: summarizeageif year >= 80, detail • Results: • Summarizes age separately for different values of black, including only observations for which year >= 80, includes extra detail.
Stata command • Example 2 • Stata Commands: .generateagelt30= age .replaceagelt30= 1if age < 30 .replaceagelt30= 0if age >= 30 & age <. • Result: variable agelt30 set equal to 1, 0, or missing • Generally [= exp] used with commands generate and replace
Stata command • Click Help / Stata command • Type key word (Ex: summarize) • See details
Do Files and Log Files • A do file is a text file with STATA code that STATA runs line by line, as if the sentences where written in the STATA command window. • A log file is a text file with all the results that appear in the STATA results window. • the user selects when to start and when to stop logging to the log file
Variable name • Have up to 32 characters but shorter names are easy to type • Stata names are case sensitive (age≠Age) • Should: • short lowercase • single word • underscore to separate word effort fpe family_planning_effort familyplanningeffort
Variable type • Nummeric variable • String variable • Missing value • numberic: dot (.) • string: “”
Some Basic Commands • computing basic statistics • summarize ypc • summarize ypcf [w=popwt] • summarize ylab [w=popwt] if age >=25 & and age <=55 • generate new variables • generate ypc2 = ypc^2 • tabulate data • table skill [w=popwt], c(mean ylab)
Some Basic Commands • renaming variables • rename ypc2 ypcf22 • eliminating variables • drop ypc22 • replacing values • replace male=0 if male==1
Open data from Excel format • Import data from excel file
