Reproducible Research Using Stata

In this presentation we shall address two issues concerning the research process: (1) the need for an efficient way to transfer results obtained using a statistical package into a written report, and (2) the need to organize and to package one's work so that those results are easily reproducible. Previous work addressing these issues has concentrated on tools written specifically for use with S-Plus/R and LaTeX, and has involved mixing code and written material in a single document (e.g., Sweave). In contrast, our approach involves a method for extracting results (e.g., estimation results, graphs, and even pieces of code and/or raw output) generated by a suitably organized do-file (or files) into a series of intermediary files which can then be easily imported into a second, written document. Although the document could be constructed in a variety of formats, we shall demonstrate how this may done using reStructuredText -- an intuitive and easy-to-use markup syntax which can then be automatically translated into a variety of final formats (e.g., LaTeX, HTML). This system may be used not only for research but also when teaching statistics with Stata as a method for students to organize and to submit their work.

The prognostic value of a nomogram for exercise capacity in women

BACKGROUND: Recent studies have demonstrated that exercise capacity is an independent predictor of mortality in women. Normative values of exercise capacity for age in women have not been well established. Our objectives were to construct a nomogram to permit determination of predicted exercise capacity for age in women and to assess the predictive value of the nomogram with respect to survival. METHODS: A total of 5721 asymptomatic women underwent a symptom-limited, maximal stress test. Exercise capacity was measured in metabolic equivalents (MET). Linear regression was used to estimate the mean MET achieved for age. A nomogram was established to allow the percentage of predicted exercise capacity to be estimated on the basis of age and the exercise capacity achieved. The nomogram was then used to determine the percentage of predicted exercise capacity for both the original cohort and a referral population of 4471 women with cardiovascular symptoms who underwent a symptom-limited stress test. Survival data were obtained for both cohorts, and Cox survival analysis was used to estimate the rates of death from any cause and from cardiac causes in each group. RESULTS: The linear regression equation for predicted exercise capacity (in MET) on the basis of age in the cohort of asymptomatic women was as follows: predicted MET = 14.7 - (0.13 x age). The risk of death among asymptomatic women whose exercise capacity was less than 85 percent of the predicted value for age was twice that among women whose exercise capacity was at least 85 percent of the age-predicted value (P<0.001). Results were similar in the cohort of symptomatic women. CONCLUSIONS: We have established a nomogram for predicted exercise capacity on the basis of age that is predictive of survival among both asymptomatic and symptomatic women. These findings could be incorporated into the interpretation of exercise stress tests, providing additional prognostic information for risk stratification