Data management made easy

Data management and data cleaning are critically important steps in any data analysis. Many of us learned this lesson the hard way. Have you ever fit a model that includes age as a covariate and forgotten to convert the missing value codes of -99 to missing values? I have. Or maybe you overlooked a data entry error that resulted in an age of 354 that should have been 54. I’ve done that too. Careful data management and cleaning can help us avoid these kinds of embarrassing mistakes.

I recently recorded a series of data management videos for the Stata Youtube Channel. You can click on the links below to watch the videos. I included topics that I think are important, but the list is far from exhaustive. If you would like to see videos on additional topics, please leave your suggestion in the comments below.

Data management playlist

You can learn more about these topics and many others in the Data Management Reference Manual.

Nonlinear multilevel mixed-effects models

You have a model that is nonlinear in the parameters. Perhaps it is a model of tree growth and therefore asymptotes to a maximum value. Perhaps it is a model of serum concentrations of a drug that rise rapidly to a peak concentration and then decay exponentially. Easy enough, use nonlinear regression ([R] nl) to fit your model. But … what if you have repeated measures for each tree or repeated blood serum levels for each patient? You might want to account for the correlation within tree or patient. You might even believe that each tree has its own asymptotic growth. You need nonlinear mixed-effects models—also called nonlinear hierarchical models or nonlinear multilevel models. Read more…

Working with Java plugins (Part 2)

In my previous post, I talked about how to combine the Java library Twitter4J and Stata’s Java function Interface using Eclipse to create a helloWorld plugin. Now, I want to talk about how to call Twitter4j member functions to connect to Twitter REST API, return Twitter data, and load that data into Stata using the Stata SFI. Read more…

Categories: Programming Tags: , ,

Working with Java plugins (Part 1)

Introduction

Three months ago, I wrote about a new command, twitter2stata, that imports data from Twitter’s REST API into Stata. Today, I will show you the tools we used to develop this command. Writing this command from scratch solely in Mata or ado-code would have taken several months. Fortunately, we can significantly speed up our development using an existing Java library (Twitter4J) and Stata’s Java plugins. In this post, I will discuss the basic steps of how to leverage a Java library and the Stata Java API.

Java is the most popular programming language in the world, so there are many libraries to support your development. A quick Google search should tell you if a Java library exists for what you are trying to do; this is how we found the library Twitter4J. For the rest of this blog entry, a basic understanding of programming in Java is helpful, but not necessary. Read more…

Categories: Programming Tags: , ,

Importing WRDS data into Stata

Wharton Research Data Services (WRDS) is a leading research platform and business intelligence tool for 400+ corporate, academic, and government researchers. If your institution subscribes to WRDS, you can now easily access WRDS data remotely via Stata’s odbc command. For questions or subscription information click here. Read more…

Bayesian logistic regression with Cauchy priors using the bayes prefix

Introduction

Stata 15 provides a convenient and elegant way of fitting Bayesian regression models by simply prefixing the estimation command with bayes. You can choose from 45 supported estimation commands. All of Stata’s existing Bayesian features are supported by the new bayes prefix. You can use default priors for model parameters or select from many prior distributions. I will demonstrate the use of the bayes prefix for fitting a Bayesian logistic regression model and explore the use of Cauchy priors (available as of the update on July 20, 2017) for regression coefficients. Read more…

Importing data with import fred

Introduction

The Federal Reserve Economic Database (FRED), maintained by the Federal Reserve Bank of St. Louis, makes available hundreds of thousands of time-series measuring economic and social outcomes. The new Stata 15 command import fred imports data from this repository.

In this post, I show how to use import fred to import data from FRED. I also discuss some of the metadata that import fred provides that can be useful in data management. I then demonstrate how to use an advanced feature: importing multiple revisions of series whose observations are updated over time. Read more…

Categories: Data Management Tags: ,

Importing Twitter data into Stata

In the past, we’ve had users ask if Stata could import Twitter data. So we asked one of our interns, Dawson Deere (currently working on his computer science degree at Texas A&M University) to see if he could write a new command to do this. He used Stata 15’s improved Java plugins feature to write a new twitter2stata command. To install twitter2stata, type

ssc install twitter2stata, replace

Read more…

Categories: Data Management Tags: ,

Estimating the parameters of DSGE models

Introduction

Dynamic stochastic general equilibrium (DSGE) models are used in macroeconomics to model the joint behavior of aggregate time series like inflation, interest rates, and unemployment. They are used to analyze policy, for example, to answer the question, “What is the effect of a surprise rise in interest rates on inflation and output?” To answer that question we need a model of the relationship among interest rates, inflation, and output. DSGE models are distinguished from other models of multiple time series by their close connection to economic theory. Macroeconomic theories consist of systems of equations that are derived from models of the decisions of households, firms, policymakers, and other agents. These equations form the DSGE model. Because the DSGE model is derived from theory, its parameters can be interpreted directly in terms of the theory.

In this post, I build a small DSGE model that is similar to models used for monetary policy analysis. I show how to estimate the parameters of this model using the new dsge command in Stata 15. I then shock the model with a contraction in monetary policy and graph the response of model variables to the shock. Read more…

Categories: Statistics Tags: ,

Nonparametric regression: Like parametric regression, but not

Initial thoughts

Nonparametric regression is similar to linear regression, Poisson regression, and logit or probit regression; it predicts a mean of an outcome for a set of covariates. If you work with the parametric models mentioned above or other models that predict means, you already understand nonparametric regression and can work with it.

The main difference between parametric and nonparametric models is the assumptions about the functional form of the mean conditional on the covariates. Parametric models assume the mean is a known function of \(\mathbf{x}\beta\). Nonparametric regression makes no assumptions about the functional form.

In practice, this means that nonparametric regression yields consistent estimates of the mean function that are robust to functional form misspecification. But we do not need to stop there. With npregress, introduced in Stata 15, we may obtain estimates of how the mean changes when we change discrete or continuous covariates, and we can use margins to answer other questions about the mean function.

Below I illustrate how to use npregress and how to interpret its results. As you will see, the results are interpreted in the same way you would interpret the results of a parametric model using margins. Read more…