Browsing by Subject "Yield"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Restricted
    Limits to the use of environmental indices to reduce risk and/or increase yield in the South African anchovy fishery
    (National Inquiry Services Centre, 2005) De Oliveira, J A A; Butterworth, Doug S
    Environmental indices that provide short-term predictions of recruitment have the potential to improve the average yield from highly productive resources that sustain recruit fisheries without an associated increase in risk (of resource 'collapse'). This is particularly true for cases where a measurement of recruitment is not available until after substantial fishing on this recruitment has already taken place. The South African anchovy Engraulis encrasicolus resource reflects such a situation, and forms the basis for a simulation study to investigate the benefits of using environmental indices to set appropriate Total Allowable Catches (TACs). Simulations, based on a 'management procedure' (sensu the International Whaling Commission), investigate how such benefits are related to the proportion of variation in recruitment explained by the environmental index. Furthermore, they evaluate to what extent these benefits are compromised by uncertainties related to the degrees of freedom effect (over-fitting data), the selection of explanatory variables (danger of spurious correlations), and errors in the values of explanatory variables (including measurement error). Five recruitment prediction models that incorporate increasing numbers of these uncertainties are investigated. These predictions are used to adjust TACs depending on whether they indicate forthcoming recruitment to be in the top or bottom third of the distribution of possible recruitment values. Results indicate that an environmental index needs to explain roughly 50% or more of the total variation in recruitment (r2 ≥ 0.5) before the management procedure starts showing benefits in terms of the summary performance statistics for risk and average catch. Comparable benefits are possible at a lower r2 value when TAC constraints are removed, but there is then a large associated increase in interannual catch variation. When r2 is low, performance in terms of average catch may prove worse if attempting to take account of an environmental variable in setting the TAC than ignoring it.
  • Thumbnail Image
    Item
    Open Access
    Systematic Reviews
    (BioMed Central, 2016) Njau, Bernard; Damian, Damian J; Abdullahi, Leila; Boulle, Andrew; Mathews, Catherine
    Background: HIV is still a global public health problem. More than 75 % of HIV-infected people are in Africa, and most of them are unaware of their HIV status, which is a barrier to accessing antiretroviral treatment. Our review aims, firstly, to determine whether HIV self-testing is an effective method to increase the uptake of testing, the yield of new HIV-positive diagnoses, and the linkage to antiretroviral treatment. Secondly, we aim to review the factors that facilitate or impede the uptake of HIV self-testing. Methods/design: Participants will be adults living in Africa. For the first aim, the intervention will be HIV self-testing either alone or in addition to HIV testing standard of care. The comparison will be HIV testing standard of care. The primary outcomes will be (i) uptake of HIV testing and (ii) yield of new HIV-positive diagnoses. The secondary outcomes will be (a) linkage to antiretroviral (ARV) treatment and (b) incidence of social harms. For the second aim, we will review barriers and facilitators to the uptake of self-testing. We will search PubMed, Cochrane Central Register of Controlled Trials, Scopus, Web of Science, WHOLIS, Africa Wide, and CINAHL for eligible studies from 1998, with no language limits. We will check reference lists of included studies for other eligible reports. Eligible studies will include experimental and observational studies. Two authors will independently screen the search output, select studies, and extract data, resolving discrepancies by consensus and discussion. Two authors will use Cochrane risk of bias tools for experimental studies, the Newcastle-Ottawa Quality Assessment Scale for observational studies, and the Critical Appraisal Skills Programme (CASP) quality assessment tool for qualitative studies. Discussion: Innovative and cost-effective community-based HIV testing strategies, such as self-testing, will contribute to universal coverage of HIV testing.