Discarding logic: 2008 Ancel Keys Memorial Lecture

Rigorous science as the road to better public health

In the current issue of Population Health Metrics, two reports paint a bleak picture of American public health. Both physical inactivity and obesity remain highly prevalent; yet, it is not clear that increased physical activity will reduce the burden of obesity. There continue to be widespread disparities in life expectancy across United States counties. These reports appear against a backdrop of debate regarding how we should allocate our scarce resources for improving health: should we focus more on improving access to high-quality medical care, or should we instead focus on more and better public health interventions? While optimal solutions remain obscure, a look at prior successes suggests that ultimately they will come from the conduct and implementation of rigorous science, and in particular event-driven trials.

Brief critical review: Statistical assessment of biomarker performance

INTRODUCTION

Articles have suggested that C-statistics associated with receiver operator characteristic (ROC) curves are insufficiently sensitive compared to odds/risk ratios (OR/RR) defined by p-values. Some suggest reclassification techniques are more appropriate.

METHODS

We review the concepts of p-values, OR/RR, and ROC curves. We construct a ROC curve, demonstrate parametric and nonparametric curves, and analyze a comparison of ROC curves.

RESULTS

Using these illustrations, we show that the ROC curve is not simply a C-statistic but a continuum of sensitivity/specificity pairs over decision levels. We demonstrate that p-values provide little useful information about discrimination and that OR/RR is a limited expression of a sensitivity/specificity plot. We illustrate that low prevalence produces low positive predictive values, reclassification techniques are subject to the same rules of prevalence as other analysis, and that modifying the analysis can decrease the p-value comparing C-statistics without altering the sensitivity/specificity plot.

CONCLUSIONS

ROC curves provide both visual and statistical information to support entry into large-scale trials, determining decision levels and the use of testing in the absence of such trials. If the sensitivity/specificity plot shows little improvement at appropriate decision point(s), statistically significant-improvement in other "novel" statistical indices should be suspect.

Imaging assessment of cardiovascular risk in asymptomatic adults

OBJECTIVE

This article will address the role of coronary artery calcium (CAC) and carotid intima-media thickness screening in asymptomatic at-risk adults and the broader concept of vulnerable plaque as it applies to this population.

CONCLUSION

Imaging for assessment of cardiovascular risk in asymptomatic adults has been the subject of considerable interest and some controversy. The incorporation of CAC and carotid intima-media thickness assessment into recent guidelines reflects the growing evidence base for these applications.

Imaging of subclinical atherosclerosis: questions and answers

An increasingly important public health issue is the identification, stratification, and optimal management of individuals with subclinical atherosclerosis. This review addresses those aspects of noninvasive imaging of subclinical atherosclerosis that are most available and relevant to the practicing radiologist.