Stata Frequently Asked Questions

Can't find your question? Try checking our General FAQ page.

Transferring data to/from Stata

• How can I convert files among SAS, SPSS and Stata?
• How can I read Excel files in Stata? (Stata 12)
• How can I read Stata 12 data files in Stata 11?
• How do I export Stata .dta files to comma-separated files?
• How do I export Stata .dta files to a SAS Xport file?
• How can I load, write, or view a dBASE file, Excel file or Access file using odbc?
• How can I convert a Stata file to an MLwiN file using Stata program stata2mlwin?
• How can I convert a Stata file to an Mplus file?
• Stata to HLM
  • Easiest: How do I convert a Stata file to HLM?
  • Harder: How can I convert a Stata file to an HLM file using HLM Windows interface?
  • Harder: How to separate a Stata single file into multiple data files for analysis in HLM software?
• How can I input a dataset quickly?
• How do I read a data file that uses commas/tabs as delimeters?
• How can I output a formatted ASCII file?
• How do I load large data sets (> 1GB) under 32-bit Windows? (from Stata FAQs)

Stata Graphical User Interface (for Windows)

• How do I make windows dock, pin, and float? (shown as a movie)
• How do I load window settings? (shown as a movie)
• How do I save window settings? (shown as a movie)
• How do I set other window preferences? (shown as a movie)
• How do I change the font (PC version)?

General Use and Data Management

• How can I anonymize patient IDs and still be able to decode them, if necessary?
• How can I sort data within rows independently for each observation?
• How can I create all pairs within groups?
• How do I copy Stata output and Stata graphs into Word?
• How can I save the contents of the results window?
• How can I make the results window hold more results?
• How do I update my copy of Stata?
• How do I check that the same data input by two people are consistently entered?
• How can I list observations in blocks?
• Can I do by and sort in one command?
• Why am I losing precision with large whole numbers (such as an ID variable)?  
• How can I quickly recode continuous variables into groups?
• How do I standardize variables (make them have a mean of 0 and sd of 1)?
• How can I randomly assign observations to groups in Stata?
• How can I draw a random sample of my data?
• How can I read dates with both 2-digit abd 4-digit year?
• How can I "fill down"/expand observations with respect to dates and then update my dates?
• How can I count the number of days between two dates?
• How do I assign the values of one variable as the value labels for another variable?
• How can I detect duplicate observations?
• How can I access information stored after I run a command in Stata (returned results)?
• How can I identify cases used by an estimation command using e(sample)?
• How can I sample from a datasets with frequency weights?
• How do I document and search a Stata dataset?
• How can I create dyad IDs?
• Files
• How can I generate automated filenames in Stata?
• How can I merge multiple files in Stata?
• How can I combine a large number of files?

Missing values

• Can I quickly see how many missing values a variable has?
• How can I see the number of missing values and patterns of missing values in my data file?
• How can I quickly recode missing values into different categories?
• How can I use multiply imputed data where original data is not included?

String variables

• How can I quickly convert many string variables to numeric variables?
• How can I turn a string variable containing dates into a date variable Stata can recognize?
• How can I extract a portion of a string variable using regular expressions?

Error messages

• How can I handle the matsize too small error?
• How can I handle the No Room to Add Observations error?

How does Stata compare with SAS and SPSS?

• How do I do this SAS Command in Stata?
• How do I do this SPSS Command in Stata?

General Statistics

• How can you get 3-way, 4-way, 5-way or more cross tabulations in Stata?
• How can I compute power for contingency tables in Stata?
• How can I get descriptive statistics and the five number summary on one line?
• Why do I get different values of kurtosis in SAS, Stata and SPSS?
• What are the differences between one-tailed and two-tailed tests?

Margins Command

• How can I get margins for a multiply imputed survey logit model? (Stata 12)
• How can I get margins and marginsplot on multiply imputated data? (Stata 12)
• How can I get anova type results from xtmixed using the margins command? (Stata 11)
• How can I use the margins command to understand multiple interactions in regression and anova? (Stata 11)
• More of how can I use the margins command to understand multiple interactions in regression? (Stata 11)
• How can I use the margins command to understand multiple interactions in logistic regression? (Stata 11)
• How can I use margins to understand a categorical by categorical by continuous 3-way interaction? (Stata 11)
• How can I graph the results of the margins command? (Stata 11) (Stata 12)
• How can I use the margins command with a 3-way anova interaction? (Stata 11)
• How can I get anova simple main effects with the margins command? (Stata 11)
• How can I do anova contrasts using the margins command? (Stata 11)
• How can get anova main-effects with dummy coding using margins? (Stata 11)
• Why doesn't the margins command work with a nested factor in anova? (Stata 11)
• How can I do simple main effects using anovalator? (Stata 11)
• How do I use the anovalator command? (Stata 11)

Regression

• Interactions and comparing coefficients across groups
  • Everything you always wanted to know about contrasts* (*But were afraid to ask)
  • How can I understand a 3-way continuous interaction? (Stata 10: Part 1, Part 2), (Stata 11: Part 1, Part 2), (Stata 12)
  • How can I understand a continuous by continuous interaction? (Stata 10) (Stata 11) (Stata 12)
  • How can I understand a categorical by continuous interaction? (Stata 10) (Stata 11) (Stata 12)
  • What happens if you omit the main effect in a regression model with an interaction?
  • Why don't my anova and regression results agree? (Stata 11)
  • How can I get anova main-effects with dummy coding? (Stata 10)
  • How can I compare regression coefficients between 2 groups?
  • How can I compare regression coefficients across 3 (or more) groups?
• Regression graphics
  • How can graphically compare OLS and BLUP results in Stata?
  • How can I do a scatterplot with regression line in Stata?
• Types of regression
  • How can I get an R² with robust regression (rreg)?
  • How do I interpret quantile regression coefficients?
  • How does one do regression when the dependent variable is a proportion?
  • What is seemingly unrelated regression and how can I perform it in Stata?
  • How can I analyze count data in Stata?
  • How can I use countfit in choosing a count model?
  • How does xtreg-re differ from xtreg-fe?
• How can I estimate effect size for xtmixed?
• How can I compute effect size in Stata for regression?
• How can I generate fungible regression weights?
• Comparing various methods of analyzing clustered data in Stata.
• How can I create dummy variables in Stata?
• Can I make regression tables that look like those in journal articles?
• How can I run a piecewise regression in Stata?
• How can I find where to split a piecewise regression?
• How can I perform the likelihood ratio, Wald, and Lagrange multiplier (score) test in Stata?
• How Can I Perform Post Estimation Tests with Multiply Imputed Datasets?
• How Can I Estimate R-squared for a Model Estimated Using Multiply Imputed Data?

Mediation

• How can I compute indirect effects with imputed data? (Method 2)
• How can I compute indirect effects with imputed data? (Method 1)
• How can I get Monte Carlo standard errors for indirect effects?
• How can I compare indirect effects in a multiple group model? (Stata 12)
• How can I do mediation analysis with the sem command? (Stata 12)
• How can I perform mediation with multilevel data? (Method 2)
• How can I perform mediation with multilevel data? (Method 1)
• How can I perform mediation with binary variables?
• How can I do mediation analysis with a categorical IV in Stata?
• How can I do moderated mediation in Stata?
• How can I do moderated mediation with a categorical moderator using sem?
• How can I do moderated mediation with a categorical moderator in Stata?
• How can I perform Sobel-Goodman mediation tests?
• How can I analyze multiple mediators in Stata?

Logistic Regression

• How can I understand a continuous by continuous interaction in logistic regression? (Stata 11) (Stata 12)
• How can I understand a categorical by continuous interaction in logistic regression? (Stata 10) (Stata 11) (Stata 12)
• How can I understand a categorical by categorical interaction in logistic regression? (Stata 10) (Stata 11) (Stata 12)
• How can I compute predictive margins for xtmelogit with random effects?
• How can I estimate probabilities that include the random effects in xtmelogit? (Stata 11)
• How can I understand a categorical by continuous interaction in ologit? (Stata 12)
• How do I interpret odds ratios in logistic regression?
• How do I use adjust in probit or logit?
• How can I get a Somers' D after logistic regression in Stata?
• How can I estimate relative risk using glm for common outcomes in cohort studies?
• How can I test the difference in area under ROC curve for two Logistic Models?

Analysis of Variance

• Everything you always wanted to know about contrasts* (*But were afraid to ask)
• How can I get denominator degrees of freedom for xtmixed?
• How can I test simple effects in repeated measures models? (Stata 12)
• How can I understand a three-way interaction in ANOVA? (Stata 10) (Stata 11) (Stata 12)
• How can I do power and robustness analyses for factorial anova? (Stata 11)
• How can I get anova main-effects with dummy coding?
• How can I get anova type III results using xtmixed?
• How can I get anova simple main effects with dummy coding?
• Why don't my anova and regression results agree? (Stata 11)
• How can I analyze a nested model using xtmixed?
• How can I compute critical values for test of simple effects?
• How can I compute effects size after anova?
• How can I do classical ANOVA designs using xtmixed? (Stata 12)
• How can I do post-hoc pairwise comparisons in Stata?
• How can I do post-hoc pairwise comparisons of adjusted means in Stata?
• How can I do profile analysis in Stata?
• How can I do multivariate repeated measures in Stata?
• How can I plot ANOVA cell means in Stata?
• How can graph group means and standard deviations for ANOVA?
• How can I do ANOVA contrasts in Stata?
• How can I do tests of simple main effects in Stata?
• How can I check for homogeneity of variance in a factorial ANOVA design?
• How can I test for nonadditivity in a randomized block ANOVA in Stata?
• How can I determine the correct term in an ANOVA using Stata?
• How does the ANOVA command handle collinearity? (from Stata FAQs)

SEM

• Linear growth models: xtmixed vs sem
• How can I do CFA with binary variables?
• What are the saturated and baseline models in sem?
• How can I do mediation analysis with the sem command? (Stata 12)
• How can I check measurement invariance using the sem command? (Stata 12)
• How can I do EFA within a CFA framework? (Stata 12)

Graphics

• How can I graph chi-square power curves in Stata?
• Where can I find examples of user written graph commands for Stata?
• How can I do a profile plot in Stata?
• How can graph group means and standard deviations for ANOVA?
• How can I plot ANOVA cell means in Stata?
• How can I combine a histogram and a boxplot in Stata?
• How can I make a bar graph with error bars?
• How can I use postgr3 to make graphs of predicted values after an estimation command?
• How can I graph two (or more) groups using different symbols?
• How do I graph data with dates?
• How can I view/compare different marker symbol options?
• How do I save a Stata graph as an EPS file?
• How do I use version 7 graph commands in later versions of Stata?
• How do I use xtline in Stata?
• How can I visualize longitudinal data in Stata?

Time Series

• How to collapse a daily time series to a monthly time series
• How to extract month and year component from a variable with %tm format

Capabilities

• See the Stata capabilities page for information about the capabilities of Stata, including Linear models, Binary, count, and limited dependent variables, Resampling and simulation methods, Graphics, Survey methods, Survival analysis

Advanced Statistics - Survey commands and clustering

• How do I use the Stata survey (svy) commands?
• Sample setups for commonly used survey data sets
• Choosing the correct analysis for various survey designs
• How can I check for collinearity in survey regression?
• How can I do a t-test with survey data?
• How can the standard errors with the cluster() option be smaller than those without the cluster() option? (from Stata FAQs)
• Do the svy commands handle zero weights differently than non-svy commands? (from Stata FAQs)
• How can I analyze a subpopulation of my survey data in Stata?
• Why doesn't summarize accept pweights? What does summarize calculate when you use aweights? (from Stata FAQs)
• Why doesn't the test of the overall survey regression model in Stata match the results from SAS and SUDAAN?

Advanced Statistics - Other

• How can I do multilevel principal components analysis?
• How can I access the random effects after xtmixed using _diparm?
• How can I convert a multilevel model to a mixed model?
• How can I do factor analysis with missing data in Stata?
• How can I do correspondence analysis on summary data?
• How to do parallel analysis for pca or factor analysis in Stata?
• How can I compute tetrachoric correlations?
• How can I calculate a kappa statistic for variables with unequal score ranges?
• How should I analyze percentile rank data?
• Why do estimation commands sometimes drop variables?  (from Stata FAQs)
• How can I test for equality of distribution?
• How can I test for a trend across a categorical variable?
• How do I write my own bootstrap program?
• How can I manually generate the predicted counts from a ZIP or ZINB model based on the parameter estimates?
• How can I perform multiple imputation on longitudinal data using ICE?
• How can I calculate Moran's I in Stata?
• How do I generate a variogram for spatial data in Stata?
• How can I fit a random intercept or mixed effects model with heteroskedastic errors in Stata?
• How is the 95% CI of the variance component in a mixed model calculated?

Other

• What is the difference between = and == in STATA?
• What types of weights do SAS, Stata and SPSS support?
• How do I do elementwise operations on a matrix?
• How can I get poisson probabilities in Stata?
• How can I generate a saturated model using DESMAT?
• How can I translate a file into a Postscript file?
• How do I use file write to write results or other information to an external text file?
• How do I use file read to read in information in an external text file?
• How do I use findit to search for programs and additional help?