Heterogeneity In Survival Rates Research Articles

Population parameters and heterogeneity in survival rates of Indo-Pacific humpback dolphins in a heavily urbanized coastal region of southeast China: implications for conservation

The Pearl River Delta (PRD) region on the southeast coast of China is among the largest and most populated metropolitan regions of the world, subjecting the Indo-Pacific humpback dolphins (Sousa chinensis) inhabiting coastal waters of this region – apparently the largest population of this species – to intense anthropogenic pressure. In this 5-year study (2011-2015), we applied mark-recapture techniques to quantify population parameters of humpback dolphins in the main body of the extensive estuarine system of the Pearl River, the Lingding Bay (LB), the most urbanized and industrialized part of PRD. The super-population size was estimated at 928 individuals (95% CI=823-1046), which however over-represents the latest number of extant animals. Annual estimates fluctuated between 708 and 750 dolphins, and likely reflect most accurately the latest/current number of humpback dolphins in waters of LB. Both the overall and annual estimates generated by our study are considerably lower than previously published abundance estimates. Apparent survival rates were generally low, estimated at 0.943 (SE = 0.008, 95% CI = 0.929-0.958) and 0.815 (SE = 0.025, 95% CI = 0.766-0.866) for adults and juveniles, respectively. In conjunction with limited recruitment, they may have led to a substantial decline in population numbers over the past two decades. Notably, dolphins exhibited heterogeneous apparent survival rates across the complex anthropogenic seascape of LB. Adult individuals that use Hong Kong waters as their primary habitat exhibited 6.2% higher survival rates than those in other parts of LB. This difference tripled (19.2%) for juveniles, a likely expression of their susceptibility to environmental and/or anthropogenic stresses. We suggest that the difference in survival is largely due to heterogeneous anthropogenic stressors that vary spatially across the estuary, among which habitat loss, pollution, and declining prey resources appear to be the primary threats. Based on our latest findings, we call for a strategic conservation planning with the highest priority given to preserve the remaining key dolphin habitats in Hong Kong waters, and to quantify and mitigate the impacts of major stressor(s) in Guangdong (mainland China) waters. Given the encroachment of ever-more-intense human activities on the coastal habitats of humpback dolphins, understanding their demographic response and the underlying mechanisms of the population processes may prove instrumental in the formulation of a conservation management strategy that can secure their continuous survival.

Variations in Breast Cancer Survival Rates: A Systematic Review and Meta-Analysis of Data from the Entire Continent of Africa

Background: The survival from breast cancer in Africa is poor and yet the incidence rate is on the rise. Causes of variations in survival from breast cancer are not well understood. We aimed to do a systematic review and meta-analysis on 5-year survival rates of breast cancer on the entire continent of Africa and to examine trends over time, and investigate sources of variations across the region. Methods: We searched MEDLINE, Embase, Cochrane Library to identify studies on breast cancer survival in African men and women published before October 17, 2018, and in any language. Random-effects meta-analyses were done to investigate between-study heterogeneity in 5-year survival rates of breast cancer and meta-regression analyses to identify potential sources of variation. 5-year survival rates of breast cancer in Africa were compared with similar estimates for black and white population in the USA from the Surveillance, Epidemiology, and End Results database. Findings: 54 studies were included, which consisted of 18,970 women and men from 13 African countries, 8 of which were from sub-Saharan region. There was wide between-study heterogeneity in the survival rates (mean 52.9%, range 7-91%, I2=99.1%; p<0.0001). Age and gender adjusted 5-year survival rates were lower in sub-Saharan Africa (absolute difference [AD] from North Africa [reference group] -25.4% (95% CI: -34.97 to -15.82%), lower in predominantly black population compared to predominantly white population -25.9% lower (95% CI: -35.40 to -16.43%). Within sub-Saharan region, survival rates are lower in western and eastern region compared to southern region. Although triple negative cancer negatively correlated with survival, the correlation did not reach a statistical significance (r=-0.27, p=0.35). Survival rates are increasing over time more in white Africans compared to black Africans but the survival rates for Africans are still significantly lower when compared to the black and white populations in the USA, a high-income country. Interpretation: Region and race-specific public health interventions coupled with genetic prospective studies are urgently needed to improve breast cancer survival Africa. Funding Statement: Support was provided from the unrestricted funds from the Academic Enrichment Fund of the Department of Surgery and the David L. Nahrwold Endowment in the Penn State College of Medicine (DIS). Declaration of Interests: The authors declare no competing interests. Ethics Approval Statement: For this systematic review and meta-analysis, the authors developed a study protocol based on the PRISMA guidelines.

More with less: the Almost Ideal Pension Systems (AIPS)

After exploring the rationale of pension systems, I outline the essential characteristics of ‘almost ideal pension systems’ (AIPSs), an improved version of the pay-as-you-go (PAYG) model. Depending on the policy choices, to be expressed in relative terms with parameters that range between zero and one, several—and possibly very different—forms of AIPSs can take shape: e.g. with high or low pension benefits, or with early or late retirement. (Almost) independent of the version chosen, AIPSs compare favourably in theory and in simulations to all other PAYG pension systems: for example, AIPSs are found to be superior in terms of their ability to ensure a balanced budget, intergenerational equity, resilience in the face of virtually all possible demographic and economic changes, and constancy at the preferred level for the relative economic well-being of the three basic age groups (young people, adults, and seniors). In addition, AIPSs are able to reduce, and even partly redress, the normally perverse redistributive effects that derive from heterogeneity in survival rates between subpopulation groups.

Estimation of summer flounder (Paralichthys dentatus) mortality rates using mark-recapture data from a recreational angler-tagging program

Volunteer angler-tagging programs have the potential to become a valuable tool for estimating fish mortality rates. We applied a reduced version of the Barker mark-recapture model to estimate summer flounder mortality rates using data collected by an angler-tagging program in Virginia. Over a period of 12 years, recreational anglers released 47513 summer flounder in the Chesapeake Bay and its tributaries, of which 3240 were subsequently encountered. To account for heterogeneity in survival rates arising from size-based variation in fishing pressure, we categorized individual fish into size classes and used a growth model to predict recruitment of fish into each size class. Due to concerns regarding tag loss, a double-tagging study was conducted and revealed that summer flounder tag retention rates were low for both sublegal and legal sized fish (0.5±0.08 per year). The tag-loss corrected mortality probability estimates for the 30-day period following release were approximately 0.6 for sublegal fish (<36cm) and 0.65 for larger fish. Once we compensated for this short-term mortality, we found that sublegal summer flounder experience much greater apparent annual mortality rates than larger fish. This may reflect actual differences in mortality as well as the increased likelihood of smaller fish to permanently emigrate to locations with reduced encounter probabilities. Due to these size-dependent mortality rates we were unable to estimate a natural mortality rate. We conclude that angler-tagging programs can provide some insights into fish mortality rates but, in order to do so, they must be carefully designed and account for the multiple violations of mark-recapture model assumptions.

Therapeutic strategy in unresectable metastatic colorectal cancer.

While surgery is the cornerstone treatment for early-stage colorectal cancer, chemotherapy is the first treatment option for metastatic disease when tumor lesions are frequently not fully resectable at presentation. Mortality from colon cancer has decreased over the past 30 years, but there is still a huge heterogeneity in survival rates that can be mainly explained by patient and tumor characteristics, host response factors, and treatment modalities. The management of unresectable metastatic colorectal cancer is a global treatment strategy, which applies several lines of therapy, salvage surgery, maintenance, and treatment-free intervals. The individualization of cancer treatment is based on the evaluation of prognostic factors for survival (serum lactate dehydrogenase level, performance status), and predictive factors for treatment efficacy [Kirsten rat sarcoma viral oncogene homolog (KRAS) mutation status]. The available treatment modalities for metastatic colorectal cancer are chemotherapy (fluoropyrimidine, oxaliplatin, irinotecan), anti-angiogenic agents (e.g. bevacizumab), and anti-epidermal growth factor agents (cetuximab, panitumumab). The increasing number of active compounds dictates the strategy of trials evaluating these treatments either in combination or sequentially. Alternative outcomes that can be measured earlier than overall survival are needed to shorten the duration and reduce the size and cost of clinical trials.

Modeling Heterogeneity in Survival Rates of Banded Waterfowl

A model is presented that incorporates time-specific recovery rates and heterogeneous survival rates. This model constitutes an extension of the family of models presented by Brownie et al. (1985, Statistical Inference from Band-Recovery Data-A Handbook, 2nd edition, Washington, D.C.: Fish and Wildlife Service, Department of the Interior). Numerical studies of the model under known amounts of heterogeneity investigate issues of identifiability, bias, and precision. Additional work under time-specific variation in survival rates investigates the properties of the estimation procedure. We provide an example and the theoretical foundation for extensions to other models in the Brownie et al. (1985) framework.

Heterogeneous survival rates of mallards (Anas platyrhynchos)

We analyzed data of adult mallards (Anas platyrhynchos) banded throughout North America during the past 30 years, using a model developed to estimate heterogeneity in survival rates of marked individuals. The model incorporating heterogeneity in survival rates was often the most parsimonious model for the data sets analyzed, thus constituting an advancement over previous band-recovery models. Likelihood-ratio tests indicated that significant amounts of heterogeneity existed in the data sets analyzed. We were unable to detect significant differences in heterogeneity between sexes or between birds banded prior to the hunting season (July–September) and after the hunting season (January–February) in the same areas. Heterogeneity varied widely among banding areas. Changes in reporting rates confound the estimation of heterogeneity. Adjustment of estimates of heterogeneity for differences in recovery rates in the first year after banding and subsequent years results in lower estimates of heterogeneity for mallards. Coefficients of variation of survival rates for adult mallards, adjusted for variation in recovery rates, varied from 18 to 25%.

Effect of Heterogeneous Survival on Bird-Banding Model Confidence Interval Coverage Rates

Unmodeled heterogeneity in survival rates can bias point and interval estimates of survival rate, leading to erroneous inference. I examined the effect of heterogeneous recovery and survival probabilities on confidence intervals computed for S i and S using a model that assumed no heterogeneity in the population. The rates at which nominally 95% confidence intervals constructed using Ŝ i and Ŝ#58, and their respective standard errors, covered the true population expected values were lowest for positively correlated subgroup recovery and survival probabilities