Previous trial has shown that starting ART therapy earlier (‘Early’) rather than waiting for onset of symptoms (‘Standard’) in HIV patients significantly decreases mortality. As a follow-up, researchers are interested in determining if ‘Early’ therapy significantly decreases time to...

Testing for the presence of autocorrelation in a time series is a common task for researchers working with time series data. The standard Q test statistic, introduced by Box and Pierce (1970) and refined by Ljung and Box (1978), is applicable to univariate time series and to testing for...

Inspired in the R library 'snow' and to be used in multicore CPUs, parallel implements parallel computing methods through an OS's shell scripting (using Stata in batch mode) to accelerate computations. By splitting the dataset into a determined number of clusters this module repeats a task...

Stata’s sem command includes the ability to estimate models with missing data using full information maximum likelihood estimation (FIML). One of the assumptions of FIML is that the data is at least missing at random (MAR), that is, conditional on other variables in the model, missingness is...

Fractals are some of the most beloved and recognizable mathematical objects studied. They have been traced as far back as Leibniz, but failed to receive rigorous examination until the mid-twentieth century with the many publications of Benoit Mandelbrot and the advent of the modern computer. The...

Measurement invariance is a very important requisite in multiple group structural equation modeling. It attempts to verify that the factors are measuring the same underlying latent constructs within each group. The presentation will show the use of the sem command in assessing six types of...

This presentation will describe a protocol we have developed for teaching students conducting empirical research to document their work in such a way that their results are completely reproducible and verifiable. The protocol is comprised primarily of creating and assembling a collection of...

In this presentation, we present a procedure and an illustrative application of user-written mathematical optimization programs-Linear Programming(LP) and Mixed Integer Linear Programming(MILP). The LP and MILP programs in Stata will allow researchers to easily access the Stata system and to...

GPS coordinates are collected by many organizations, however in order to derive any meaningful statistical analysis from these coordinates they need to be joined with geographical data. Previously users were required to export the GPS data out of Stata and into a GIS mapping program to map the...

When estimating discrete choice models, the mixed logit approach is commonly superior to simple conditional logit setups. Mixed logit models not only allow the researcher to implement difficult random components but also overcome the restrictive IIA assumption. Despite these theoretical...