P1253296661AfPWK

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INTRODUCTION TO STATA Third group training course
in application of information and communication
technology to production and dissemination of
official statistics 10 May 11July 2007
Gereltuya Altankhuyag, Lecturer/Statistician,
UNSIAP gereltuya_at_unsiap.or.jp
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Objectives

• Gain experience in using STATA to
• Obtain descriptive statistics
• Tabulate
• Create Graphs
• Convert data files
• Create Do-files
• Create Log-files
• Use user written programs - Ado-files

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Method of teaching

• Lectures using PowerPoint slides
• Performance of in-class practical exercises using
  real survey datasets
• Group assignment
• Presentation of group assignment
• Note Subject to availability of datasets

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Contents

• Resources for learning and using Stata
• Getting started with Stata
• Basic commands to inspect datasets
• Basic commands to create and change variables,
  labeling etc.
• Basic commands to reorganize datasets
• Advanced commands merging and appending

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Contents

• Basic commands of statistics
• Basic commands of graphics
• Programming using do files
• Use of ado-files
• Creating log-files
• Inputting data from keyboard, a file or
  spreadsheet

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(No Transcript)
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Resources for learning and using STATA

• STATA
• Is a statistical package for managing, analyzing
  and graphing data.
• Has both a command and menu driven interface.
• Is Designed for research.
• Has cross platform compatibility Windows, MacOS,
  Unix, Solaris.

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Resources for learning and using STATA

• STATA
• Has three versions
• Small (restricted version) this is not
  available for Unix
• Intercooled (full version)
• Special Edition STATA/SE
• Newest release Version 9 we will use

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Resources for learning and using STATA
Stata/SE Intercooled Stata Small Stata
Speed Fastest Very Fast Fast
No. of variables 32766 2047 99
Observations Memory dependent Memory dependent 1000 (approx)
String variable 244 chars 80 chars 80 Chars
Matrices 11000 x 11000 800 X 800 40 X 40
Version Professional Professional Small computers
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Resources for learning and using STATA

• Manuals
• Getting Started
• Users Guide
• Reference
• The Stata website http//www.stata.com
• The Stata Press website - contains datasets used
  throughout the Stata manuals
• http//www.stata-press.com

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Resources for learning and using STATA

• Additional subject-specific volumes may be
  purchased separately. These include
• Longitudinal/Panel Data Reference Manual
• Mata Reference Manual
• Multivariate Statistics Reference Manual
• Programming Reference Manual
• Survey Data Reference Manual
• Survival Analysis and Epidemiological Tables
• Reference Manual
• Time-Series Reference Manual.

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Resources for learning and using STATA

• The Stata listserver an active group of Stata
  users communicate over Internet
• The Stata journal reviewed papers, regular
  columns, user-written software http//www.stata-jo
  urnal.com/
• NetCourses offers training via the Inernet
• Books and other support materials

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Resources for learning and using STATA

• Technical support by email, phone or fax
• tech_support_at_stata.com
• To subscribe to Statalist, send email to
• majordomo_at_hsphsun2.harvard.edu
• body of message subscribe statalist

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Resources for learning and using STATA

• Searchable Statalist archives at
• http//www.stata.com/statalist/archive
• This includes requests for programs, solutions
  or advice, as well as answers and general
  discussions.

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Resources for learning and using STATA

• STATA Features
• Command prompt driven
• Batch mode
• Interactive mode
• Modularity in its nature Stata code can be
  shared, reused and easy to write extensions.
• Can incorporate survey design into estimation
  process.

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Resources for learning and using STATA

• STATA Capabilities
• Elementary and Specialized Statistical Analysis
• Graphics most 2D
• Data Management user-friendly
• Matrix Operations

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Resources for learning and using STATA

• Why STATA?
• Precise estimation for complex surveys
• User-written programs for non-standard estimation
• Excellent tools for panel data analysis
• Many econometric routines
• Command driven (in new version, menu-driven as
  well)

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Resources for learning and using STATA

• Why STATA?
• Runs efficiently on many platforms
• Concise and clear documentation (with friendly
  technical support)
• Cost less to buy
• Contact stata_at_stata.com
• or visit http//www.stata.com

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• Getting Started with STATA

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Getting Started

• STARTING UP
• Click Start ? Programs ? Stata ? StataSE 9
• Alternatively, from Windows Explorer, go to
  folder
• c\stata9
• Double click
• wstata.exe

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Getting Started
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Getting Started
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Getting Started

• Verifying version and installation of Stata
• Command called verinst
• Syntax verinst
• Result
• verinst
• You are running Stata/SE 9.2 for Windows.
• Stata is correctly installed.
• You can type exit to exit Stata.

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Getting Started

• Comparing updates
• Update
• Stata executable
• folder \\Unitednations\Stata9\
• name of file wsestata.exe
• currently installed 21 Nov 2006
• Ado-file updates
• folder \\Unitednations\Stata9\a
  do\updates\
• names of files (various)
• currently installed 21 Nov 2006
• Recommendation
• Type -update query- to compare these dates
  with what is available from
• http//www.stata.com.

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Getting Started
RESULTS WINDOW results and commands displayed
here
REVIEW WINDOW past commands appear here
VARIABLE WINDOW variable list shown here
COMMAND WINDOW commands typed here
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Getting Started

• If at least one of the 4 Windows has not
  displayed, say, VARIABLE WINDOW, click on
• Window ? Variables
• or press CTRL6
• You can type in only in Command Window
• You cannot close Results and Command Windows

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Getting Started

• Window Colors
• Click on Prefs ? General Preferences

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Getting Started

• Fonts of Windows
• The fonts or font size may be changed in each
  window by clicking the upper left window button
  and then clicking on Font.

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Getting Started

• The Command window
• Page Up Steps backwards through the command
  history
• Page Down Steps forward through the command
  history
• Tab Auto-completes a partially typed variable
  name

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Getting Started

• The Review window
• To enter a command from the Review window
• Click once on a past command to copy it to the
  Command window
• Double-click on a past command to copy it to the
  Command window and execute it

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Getting Started

• The Review window
• Right-clicking on the Review window displays
• Save Review Contents
• Copy Review Contents to Clipboard
• Font

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Getting Started

• The Variables window
• To enter a variable from the Variable window
• Click once on a variable to copy it to the
  Command window
• Double-click on a variable and the variable will
  be copied twice
• Right-clicking on the Variables window displays a
  menu
• Define Notes for Variable varname to open the
  Notes dialog for variable varname
• Font

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Getting Started
MENU BAR
TOOL BAR
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Getting Started

• Ask participants to open STATA
• Ask participants to open each command of menu bar
  and explain it.
• Ask participants to point cursor at each command
  of tool bar and explain it.

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Getting Started

• In Help Option of Menu/Header bar
• Contents (for beginners unfamiliar with STATA
  commands)
• Search (for users who know the name of the
  command or topic they wish to search)

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Getting Started

• Obtaining Online Help on Commands
• For a user who wants more info on the regress
  command, enter
• help regress
• or use the Menu bar
• Help ? STATA Command

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Getting Started

• Obtaining Topic Search
• We can do a search with the Menu bar
• Help ? Search
• If you want to learn about regression, type
• search regression
• or about memory management
• search memory

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Getting Started

• Obtaining Net Search
• In the Searchpop-up window,we can also do
  aninternet search.
• Alternatively, we can issue the command
• net search regression
• to search on regression

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Getting Started

• Four ways of quitting from Stata
• Enter in Command Window
• exit
• Press ALT-F4 keys
• Click on
• File ? Exit/Clear
• Click on Close button (X at upper right hand
  corner of Stata window).

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Getting Started

• Reading Pre-Existing Stata Dataset
• (1) When the data set is very large, we may want
  to enter
• set mem 64m
• Results
• Current memory allocation
• current
  memory usage
• settable value description
  (1M 1024k)
• ----------------------------------------------
  ----------------------
• set maxvar 5000 max. variables
  allowed 1.733M
• set memory 64M max. data space
  64.000M
• set matsize 400 max. RHS vars in
  models 1.254M
• 
  
  -----------
• 
  66.987M
• (2) STATA can read only one dataset at a time.

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Getting Started

• Reading Pre-Existing Stata Dataset
• In folder c\intropov\data, we have three Stata
  files, suppose we wish to read hh.dta, then
  enter
• use c\intropov\data\hh.dta
• or alternatively, issue the two commands
• cd c\intropov\data
• use hh
• Stata datasets have extension names as dta

NOTE The Default folder is c\DATA We use the CD
command to change directory
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Getting Started clear

• Deletes all contents ( data, variables, labels)
  from the STATA memory
• Does not delete any data already saved to the HD
• Does not clear Review window contents
• It does not need any arguments
• Syntax
• clear

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Getting Started clear

• Use of clear command
• cd c\intropov\data
• clear
• use hh
• Or
• use hh, clear or
• use c\intropov\data\hh.dta, clear

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Getting Started -Arithmetic operators

• addition
• - subtraction
• multiplication
• / division
• power

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Getting Started - Relational operators

• gt Greater than
• lt Less than
• gt More than or equal
• lt Less than or equal
• Equal
• Not equal
• ! Not equal

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Getting Started - Logical operators

• Not
• And
• Or

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Getting Started - Numlist

• Numlist a list of numbers.
• 1/3 three numbers 1, 2, 3
• 3/1 the same three numbers in reverse order
• -8/-5 four numbers -8, -7, -6, -5
• 1 2 to 4 four numbers 1, 2, 3, 4
• 10 15 to 30 five numbers 10, 15, 20, 25, 30
• 1 24 same as 1 2 to 4
• 10 1530 same as 10 15 to 30
• 1(1)3 three numbers 1, 2, 3
• 1(2)9 five numbers 1, 3, 5, 7, 9
• 9(-2)1 five numbers 9, 7, 5, 3, and 1
• 1 2 3/5 8(2)12 eight numbers 1, 2, 3, 4, 5, 8,
  10, 12

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Getting Started - Syntax

• The basic Stata language syntax is
• by varlist command varlist exp if exp
• in range weight ,options

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Getting Started

• varlist denotes a list of variable names
• exp denotes an algebraic expression
• command denotes a Stata command
• options denotes a list of options. Many
  commands take command-specific options. Options
  are indicated by typing a comma at the end of the
  command, followed by the options you want to use.
  For instance sum, details

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Getting Started

• if / by / in
• these are not commands
• associated with commands when a condition needs
  to be satisfied

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Getting Started

• if exp - restricts the scope of a command to
  those observations for which the value of the
  expression is true
• if exp - is added at the end of a command with
  associated variable if any
• Syntax
• command .. if sex male

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Getting Started

• by varlist asks Stata to repeat a command for
  each subset of the data for which values of the
  variables in the varlist are equal
• by varlist - is added before a command followed
  by variable name and then command
• Syntax
• by sex command .
• Note sort dataset by sex and then run this
  syntax.

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Getting Started

• in range restricts the scope of the command to a
  specific observation range.
• in range - is added at the end of command with
  associated variable if any
• Syntax
• Command in 1 / 100

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Getting Started

• Command, option and variable names may be
  abbreviated to the shortest string of characters
• . summarize region, detail
• . sum reg,d
• Stata respects case Stata commands are lowercase
• Summarize, SUMMARIZE and summarize are three
  distinct names

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Getting Started - naming

• A name is a sequence of one to 32 letters (A-Z
  and (a-z), digits (0-9) and underscores (_).
• The first character of a name must be a letter or
  an underscore
• Not begin variable names with an underscore
• All of Statas buil-in variables begin with an
  underscore

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Getting Started - naming

• Stata reserves the following names

_all double long _rc
_b float _n _se
byte if _N _skip
_coef in _pi using
_cons int _pred with
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Getting Started prefix commands

• Prefix commands are used to prefix Stata commands
• An example of prefix command Syntax
• by varlist, option
• by region, sort sum educhead agehead
• region is bys varlist
• Sort is bys option

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Getting Started prefix commands

• Examples of prefix commands in Stata are

Prefix commands Description
by Run command on subset of data
svy Run command and adjust results for survey sampling
stepwise run command with stepwise variable inclusion /exclusion
Capture run command and capture its return code
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Getting Started - weight

• Weight used for
• Estimation of population from a sample
• Compensate under/over representation of HH in a
  sample

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Getting Started - weight

• Weight indicates the weight to be attached to
  each observation. The syntax of weight is
• weightwordexp
• weightword is not Stata commands
• Where weightword is one of

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Getting Started - weight
Weightword Meaning
Weight Default treatment of wieghts
fweight Frequency weights
pweight Sampling weights
aweight Analytic weights
iweight Importance weight
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Getting Started - weight

• Frequency weight (fweight)
• indicates the number of duplicated observations.
  Must take integer values.
• For instance if fweight associated with an
  observation is 5, that means there are 5 such
  observations each identical.
• Syntax
• command var weightwordweightvar

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Getting Started - weight

• Sampling weight (pweight)
• the inverse of the probability that this is
  included observation was sampled.
• For instance pweight of 100 indicates that this
  observation is representative of 100 subjects
• Syntax
• Command varname weightwordweightvar

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Getting Started - weight

• Analytic weight (aweight)
• Inversely proportional to the variance of an
  observation (d2/wj). It means that the variance
  of jth observation is assumed to be (d2/wj).
• Useful when working with data that contain
  averages.
• Syntax
• command varname weightwordweightvar

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Getting Started - weight

• importance weight (iweight)
• No formal definition available
• Indicates the relative importance of the
  observation
• Syntax
• Command varname weightwordweightvar

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• To be continued.

Now please proceed to perform EXERCISE 1