ECO 332 Tutorial Stata, Spring 2016

Introduction to Stata: Part II Working with Stata Looking at the data • Let us . sysuse auto to begin our session with the data. • What kind of data is there? Type . describe price to get an overall picture. • to get a listing of existing variables and observations . list price Looking at the data • Summary statistics . summarize price . summarize price, d • Two-way tables . use this procedure when you want to look at 2-way frequencies of your categorical data . tab foreign rep78 • We can get the correlation: . correlate price mpg 4 Options within the Data menu 5 Results from codebook and summarize 6 An example of a dialogue box Dialogue results from using the menu sequence Data,  Describe data,  Describe data contents (codebook) Looking at the data • Graph . histogram price • sysuse uslifeexp2 – scatter le year – scatter le year, connect(l) – scatter le year, connect(l) msymbol(i) Creating a new variable • Let us . sysuse auto • A natural step further in your data management is to create some new variables . gen gpm = 100/mpg . gen lgpm = ln(mpg) Important issues • Formatting output – Highlight results – EditCopy table • Missing data • Rename variables Estimation • OLS model: Interpreting Regression Output – reg price mpg foreign – Coefficients – Standard Error of the coefficients – CI – R2 Estimation Predictions • calculate the fitted values and residuals – fitted values: predict pprice – residuals: predict resid, residuals Plotting the Data and a Linear Fit • We can inspect the quality of the fit – graph twoway (scatter price mpg) (lfit price mpg) Estimation • Hypotheses testing – t-test: in the table – F-test: in the table – We could also run F-test: • reg rep78 price weight • test price weight Testing for Heteroskedasticity • White test : – reg price mpg foreign – estat imtest, white • Breusch-Pagan test : – reg price mpg foreign – estat hettest, normal Robust standard error • We add the option robust at the end of the regression command: – reg price mpg foreign, robust WLS estimator • reg price mpg foreign • reg price mpg foreign, robust • vwls price mpg foreign probit and logit models • probit foreign weight mpg • logit foreign weight mpg Panel data • We use nlswork.dta • tsset • Fixed effect: – xtreg hours birth_yr age race, fe • Random effect: – xtreg hours birth_yr age race, re Resuming Stata • Launch Stata: • Old commands are in the do-file. To see it, – In do-file editor • FileOpen • Find X:\intro.do Running a Do-file • To run your old commands, – FileDo… – Find “X:\intro.do” Labeling values • To add labels to dummy values – DataLabels – Define label name – Add values • We can label the data direclty from the editor To learn more • Help menu (or help command) – e.g., in Command window type “help cmdlog” Exercise • Edit the do-file until it runs all the way through • This will also familiarize you with the typed versions of some commands. • http://www.reading.ac.uk/ssc/n/UBOS_DV D/Module_4/Module_4.htm