Research Methods Lecture 5 Advanced STATA

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Research Methods Lecture 5Advanced STATA

• IAN WALKER
• Module Leader
• S2.109 i.walker_at_warwick.ac.uk

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Housekeeping announcement

• Stephen Nickell (MPC and LSE)
• British Academy Keynes Lecture in Economics
• "Practical Issues in UK Monetary Policy
  2000-2005"
• Wednesday 2nd November
• Arts Centre Conference Room at 5.30pm 
• http//www2.warwick.ac.uk/fac/soc/economics/forums
  /deptsems/keynes_lecture/

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Stat-Transfer

• Use STAT-TRANSFER to convert data.
• Click on
• Stat-transfer is point and click.
• Just tell it the file name and format
• and the format you want it in.
• Click transfer.

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Stat Transfer options

• Useful options for creating a manageable dataset
  from a large one
• Keep or drop variables
• Change variable format
• E.g. float to integer
• Select observations
• E.g. where (income benefits)/famsize lt 4500
• Can be used for reading a large STATA dataset
  and writing a smaller one
• Avoids doing this in STATA itself

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Practicising

• You can import some of Statas own demo files
  using the .sysuse command
• E.g. .sysuse auto
• Many datasets are available at specific websites
• E.g. STATAs own site has all the demo data used
  in the manual examples
• You can use the .webuse command to load the files
  directly into stata without copying locally
• .webuse auto / gets the data from STATAs own
  site /
• Or .webuse set http//www2.warwick.ac.uk/fac/soc/
  economics/pg/modules/rm/notes/auto.dta

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More help

• You can search the whole of STATAs online help
  using .search xxx
• Michigans web-based guide to STATA (for SA)
• UCLA resources to help you learn and use STATA
• including movies and web-books
• Consult other user-written guides and tutorials
• Chevalier1, Chevalier2 Princeton Illinois
  Gruhn
• ESDSs Stata for LFS
• Statas own resources for learning STATA
• Stata website, journal, library, archive
• http//www.stata.com/links/resources1.html

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Web resources

• STATA is web-aware
• E.g. . update / updates from www.stata.com /
• Statalist is an email listserv discussion group
• The Stata Journal is a refereed journal
• Replaces the old Stata Technical Bulletin (STB)
• SSC Boston College STATA Archive
• Extensive library of programs by Stata users
• Files can be downloaded in Stata using . ssc
• Eg .ssc install outreg
• Installs the outreg ado file that makes tables
  pretty

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Always (whatever the software)

• Use lowercase
• Open a log file
• Label your data
• Use the do file editor
• Organise your files
• Separate directories for separate projects
• Archive (zip) data, do and results files when
  your finished

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Customising STATA

• profile.do runs automatically when STATA starts
• Edit it to include commands you want to invoke
  every time
• .set mem 200m
• .log using justincase.log, replace
• Define preferences for STATAs look and feel
• Click on Prefs in menu
• Colours, graph scheme, etc.
• Save window positioning

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Regression models - I

• Linear regression and related models when the
  outcome variable is continuous
• OLS, 2SLS, 3SLS, IV, quantile reg, Box-Cox
• Binary outcome data
• the outcome variable is 0 or 1(or y/n)
• probit, logit, nested logit...
• Multiple outcome data
• the outcome variable is 1, 2, ...,
• conditional logit, ordered probit

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Regression models - II

• Count data
• the outcome variable is 0, 1, 2, ..., occurrences
  
• Poisson regression, negative binomial
• Choice models
• multinomial choice
• A, B or C
• Multinomial logit, Random utility model,
  unordered probit, nested logit, ...etc
• Selection models
• Truncated, censored
• Tobit, Heckman selection models
• linear regression or probit with selection

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Regression models - III

• STATA supports several special data types.
• Once type is defined special commands work
• Time series
• Estimate ARIMA, and ARCH models
• Estimators for autocorrelation and
  heteroscedasticity
• Estimate MA and other smoothers
• Tests for auto, het, unit roots - h, d, LM, Q,
  ADF, P-P ..
• TS graphs
• sysuse tsline2, clear
• tsset day
• tsline calories, ttick(28nov2002 25dec2002 ,
  tpos(in))
• ttext(3470 28Nov2002 Thanks" 3470 25dec2002
  Xmas"",orient(vert))

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gives
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Special data types survey

• Non-randomness induces OLS to be inefficient
• STATA can handle non-random survey data
• see the syv commands
• Example (stratified sample of medical cases)
• . webuse nhanes2f, clear
• . svyset psuid pweightfinalwgt,
  strata(stratid)
• . svy reg zinc age age2 weight female black
  orace rural
• . reg zinc age age2 weight female black orace
  rural

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Special data types duration

• Survival time data
• See the st commands
• .stset failtime /sets the var that defines
  duration/
• Estimates a wide variety of models to explain
  duration
• E.g. Weibull hazard model -

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Weibull example .

• ST regression supports Weibull, Cox PH and other
  options
• . streg load bearings, distribution(weibull)
• After streg you can plot bthe estimated hazard
  with
• . stcurve, cumhaz
• STATA allows functions to be plotted by
  specifying the function

• twoway (function y .5x(-.5), range(0 5)
  yvarlab("a.5") )
• ( function y 1.5x(.5), range(0 5)
  yvarlab("a1.5") )
• ( function y 1x(0), range(0 5) yvarlab("a1")
  )
• ( function y 2x, range(0 2) yvarlab("a2") )
• , saving(weib1, replace)
• title("Weibull hazard lambda1, alpha varying")
• ytitle(hazard) xtitle(t)

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gives..
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Special data types Panel data

• STATA can handle panel data easily
• see the xt commands
• Common commands are
• .xtdes Describe pattern of xt data
• .xtsum Summarize xt data
• .xttab Tabulate xt data
• .xtline Line plots with xt data
• .xtreg Fixed and random effects

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Panel data

• An xt dataset looks like this
• pid yr_visit fev age sex height
  smokes
• ------------------------------------------
  ----------------
• 1071 1991 1.21 25 1 69
  0
• 1071 1992 1.52 26 1 69
  0
• 1071 1993 1.32 28 1 68
  0
• 1072 1991 1.33 18 1 71
  1
• 1072 1992 1.18 20 1 71
  1
• 1072 1993 1.19 21 1 71
  0
• xt commands need to know the variables that
  identify person and wave
• . iis pid
• . tis yr_visit
• Or use the tsset command
• . tsset pid yr_visit, yearly

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Panel regression

• Once STATA has been told how to read the data it
  can perform regressions quite quickly
• . xtreg y x, fe
• . xtreg y x, re

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Further advice

• See Stephen Jenkins excellent course on duration
  modelling in STATA
• See Steve Pudneys excellent course on panel
  data modelling in STATA
• Beware the dataset is 30mb