Time-to-event outcomes are common in medical research as they offer more information than simply whether or not an event occurred. To handle these outcomes, as well as censored observations where the event was not observed during follow-up, survival analysis methods should be used. Kaplan-Meier estimation can be used to create graphs of the observed survival curves, while the log-rank test can be used to compare curves from different groups. If it is desired to test continuous predictors or to test multiple covariates at once, survival regression models such as the Cox model or the accelerated failure time model (AFT) should be used. The choice of model should depend on whether or not the assumption of the model (proportional hazards for the Cox model, a parametric distribution of the event times for the AFT model) is met. The goal of this paper is to review basic concepts of survival analysis. Discussions relating the Cox model and the AFT model will be provided. The use and interpretation of the survival methods model are illustrated using an artificially simulated dataset.

Objective To identify risk factors for uterine atony or hemorrhage. Study Design Secondary analysis of a 3-arm double-blind randomized trial of different dose-regimens of oxytocin to prevent uterine atony after vaginal delivery. The primary outcome was uterine atony or hemorrhage requiring treatment. Twenty-one potential risk factors were evaluated. Logistic regression was used to identify independent risk factors using 2 complementary pre-defined model selection strategies. Results Among 1798 women randomized to 10, 40 or 80U prophylactic oxytocin after vaginal delivery, treated uterine atony occurred in 7%. Hispanic (OR 2.1; 95% CI 1.3–3.4) and non-Hispanic whites (OR 1.6; 95% CI 1.0–2.5), preeclampsia (OR 3.2; 95% CI 2.0–4.9) and chorioamnionitis (OR 2.8; 95% CI 1.6–5.0) were consistent independent risk factors. Other risk factors based on the specified selection strategies were obesity, induction/augmentation of labor, twins, hydramnios, anemia, and arrest of descent. Amnioinfusion appeared to be protective against uterine atony (OR 0.53; 95% CI 0.29–0.98). Conclusion Independent risk factors for uterine atony requiring treatment include Hispanic and non-Hispanic white ethnicity, preeclampsia and chorioamnionitis.

Masked hypertension, defined as non-elevated clinic blood pressure (BP) with elevated out-of-clinic BP, has been associated with increased cardiovascular disease (CVD) risk in Europeans and Asians. Few data are available on masked hypertension and CVD and mortality risk among African Americans (AAs). We analyzed data from the Jackson Heart Study, a prospective cohort study of AAs. Analyses included participants with clinic-measured systolic/diastolic BP (SBP/DBP)<140/90mmHg who completed ambulatory BP monitoring (ABPM) following the baseline exam in 2000–2004 (n=738). Masked daytime (10:00am–8:00pm) hypertension was defined as mean ambulatory SBP/DBP≥135/85mmHg. Masked nighttime (midnight-6:00am) hypertension was defined as mean ambulatory SBP/DBP≥120/70mmHg. Masked 24-hour hypertension was defined as mean SBP/DBP≥130/80mmHg. CVD events (nonfatal/fatal stroke, nonfatal myocardial infarction or fatal coronary heart disease) and deaths identified through December 2010 were adjudicated. Any masked hypertension (masked daytime, nighttime or 24-hour hypertension) was present in 52.2% of participants; 28.2%, 48.2% and 31.7% had masked daytime, nighttime and 24-hour hypertension, respectively. There were 51 CVD events and 44 deaths over a median follow-up of 8.2 and 8.5 years, respectively. CVD rates per 1,000 person-years (95% CI) in participants with and without any masked hypertension were 13.5 (9.9–18.4) and 3.9 (2.2–7.1), respectively. The multivariable adjusted hazard ratio (95% CI) for CVD was 2.49 (1.26–4.93) for any masked hypertension and 2.86 (1.59–5.13), 2.35 (1.23–4.50) and 2.52 (1.39–4.58) for masked daytime, nighttime and 24-hour hypertension, respectively. Masked hypertension was not associated with all-cause mortality. Masked hypertension is common and associated with increased risk for CVD events in AAs.