It is fairly simple to add an interaction term (also known as “effect modification” to epidemiologists) to a linear or logistic regression model, and test whether that term is statistically significant. However, it is much more difficult to explain what a significant interaction means in an...

Restricted cubic splines (RCSs) are used with generalized linear models and other regression methods to model complex non-linear relationships. A RCS with k knots is linear before the first and after the last knot, is a cubic polynomial between adjacent knots, and is continuous and smooth. A RCS...

An article in The Lancet discussed a clinical trial of a product for a rare disease. The authors had modified the primary analysis from an unadjusted Wilcoxon rank sum test to a Poisson regression. This led to several questions including: Was a Poisson distribution appropriate? How were the...

The University of Utah's Public Health Program, housed in the Department of Family and Preventive Medicine, uses Stata to supplement the core course, "Introduction to Biostatistics, I". All MPH/MSPH students are required to enroll in the lab component of the Biostatistics course wherein Stata is...

Most surveys collect data using complex sampling plans involving selection of both clusters and individuals with unequal probability of selection. Research in methods of using multilevel modeling (MLM) procedures to analyze such data is relatively new. Often sampling weights based on selection...

Note: I hesitate somewhat to propose this session due to the general disdain that many feel toward word processors, so you should feel free to reject it or accept it if you need to fill out the program or find it particularly interesting. Confronted with the task of producing a large appendix to...

We describe regression-based methods for analyzing multiple-source data arising from complex sample survey designs in Stata. We use the term multiple-source data to encompass all cases where data are simultaneously obtained from multiple informants, or raters (e.g., self-reports, family members,...

-gologit2- is a user-written program that estimates generalized logistic regression models for ordinal dependent variables. The actual values taken on by the dependent variable are irrelevant except that larger values are assumed to correspond to "higher" outcomes. A major strength of -gologit2-...

Efficient data cleaning and management is critical to the success of any large research project. This is particularly true in the case of longitudinal studies and/or those in which the data management tasks are shared among many individuals. Faced with several such projects, we developed a...

While scales are an integral part of the measurements involved in many research projects, few researchers make the effort to ensure that these scales are valid, reliable, uni-dimensional and consistent with relevant correlates. This presentation outlines how the Stata routine –optifact- can be...