Kaplan-Meier Estimator (kaplan-meier + estimator)

Distribution by Scientific Domains

Selected Abstracts

Survival analysis of Little Penguin Eudyptula minor chicks on Motuara Island, New Zealand

IBIS, Issue 4 2001
Chick survival of Little Penguins Eudyptula minor was studied on predator-free Motuara Island, Cook Strait, New Zealand (41d,05'S, 174d,15'E), in 1995 and 1996. We used the Kaplan-Meier estimator and robust Cox regression to estimate chick survival rate (pL se) at 0.325 pL 0.044, leading to an estimated survival from laying to fledging of 0.13 or a reproductive output of 0.26 chicks per pair and breeding attempt. Starvation posed the greatest mortality risk, followed by unknown factors and rain. Risk of death due to rain was restricted to the guard stage, whereas starvation occurred throughout the nesting period, though with a peak in the early guard stage. Significant seasonal differences in survival rate were detected in both years, but with reversed trends, survival decreasing with the season in 1995 and increasing in 1996. Failure of adults to relieve their partner on the nest after chicks hatched accounted for 16% mortality or 34% of all chick deaths. Differences in chick survival rate between nest types were significant in 1995, a year with high rainfall, but not in 1996. Nests in the base of hollow trees had the highest chick survival rate. Of chicks in open nests - a nest type that is unusual for this species - 5.4% fledged. Our results suggest that on Motuara Island good breeding sites are scarce and that the food supply has been poor during the years of this study. [source]

Improved fertility following conservative surgical treatment of ectopic pregnancy

Nannie Bangsgaard
Objective To evaluate fertility after salpingectomy or tubotomy for ectopic pregnancy. Design Retrospective cohort study. Setting Clinical University Center, Hvidovre Hospital, Copenhagen. Population Two hundred and seventy-six women undergoing salpingectomy or tubotomy for their first ectopic pregnancy between January 1992 and January 1999 and who actively attempted to conceive were followed for a minimum of 18 months. Methods Retrospective cohort study combined with questionnaire to compare reproductive outcome following salpingectomy or tubotomy for ectopic pregnancy. Cummulative probabilities of pregnancy for each group were calculated by the Kaplan-Meier estimator and compared by Cox regression analysis to control for potential confounders. Main outcome measures Intrauterine pregnancy rates and recurrence rates of ectopic pregnancy after surgery for ectopic pregnancy. Results The cumulative intrauterine pregnancy rate was significantly higher after tubotomy (88%) than after salpingectomy (66%) (log rank P < 0.05) after correction for confounding factors. No difference was found in the recurrence rate of ectopic pregnancy between the treatments (16%vs 17%). In patients with contralateral tubal pathology, the chance of pregnancy was poor (hazard ratio 0.463) and the risk of recurrence was high (hazard ratio 2.25), assessed with Cox regression. The rate of persistent ectopic pregnancy was 8%. Conclusion Conservative surgery is superior to radical surgery at preserving fertility. Conservative surgery is not followed by an increased risk of repeat ectopic pregnancy, but by the risk of persistent ectopic pregnancy, which should be taken into account when deciding on the operative procedure. Management in case of contralateral tubal pathology is disputed and should ideally be addressed in a randomised clinical trial. [source]

Five-Year Survival Distributions of Short-Length (10 mm or less) Machined-Surfaced and Osseotite® Implants

Sylvan Feldman DDS
ABSTRACT Background: In cases of reduced alveolar bone height, implants of short length (10 mm or less) may be employed although there is a perceived risk that because of their small stature they will be unable to tolerate occlusal loads and will fail to osseointegrate. Purpose: This report describes an analysis of prospective multicenter clinical studies evaluating the risk for failure of short-length implants, comparing dual acid-etched (DAE) Osseotite® implants (Implant Innovations, Inc., Palm Beach Gardens, FL, USA) to machined-surfaced implants. Materials and Methods: Admission criteria were the same for both data sets. Baseline variables of demographics including age, gender and smoking status, bone quality, location, implant dimensions, and types of prostheses were compared to ensure balance among groups. Cumulative survival rates (CSRs) were calculated with the Kaplan-Meier estimator. Results: The implant data included 2,294 implants for the DAE series and 2,597 implants for the machined-surfaced series. Patient demographics showed similar percentages of occurrence for all variables. The distributions of implants between short- and standard-length data sets for baseline variables including width, location, and restorative type were similar, qualifying these data sets for comparison of the independent variable of length. Overall, there was a 2.2% difference in 5-year CSRs between the machined-surfaced short- and the standard-length implants. For these implants a 7.1% difference was observed in the posterior maxilla and an 8.5% difference in the anterior maxilla. For DAE implants the overall difference between "standards" and "shorts" was 0.7%, which is not statistically significant. Conclusion: In this analysis the difference in CSRs between short- and standard-length implants was greater for machined-surfaced implants than for DAE implants. [source]

S41.5: Comparison of simultaneous and pointwise confidence bands for Kaplan-Meier estimators

Ralf Strobl
No abstract is available for this article. [source]