Measures of Compounding Conservatism in Probabilistic Risk Assessment

Concern about the degree of uncertainty and potential conservatism in deterministic point estimates of risk has prompted researchers to turn increasingly to probabilistic methods for risk assessment. With Monte Carlo simulation techniques, distributions of risk reflecting uncertainty and/or variability are generated as an alternative. In this paper the compounding of conservatism⁽¹⁾ between the level associated with point estimate inputs selected from probability distributions and the level associated with the deterministic value of risk calculated using these inputs is explored. Two measures of compounded conservatism are compared and contrasted. The first measure considered, F , is defined as the ratio of the risk value, R _d, calculated deterministically as a function of n inputs each at the j th percentile of its probability distribution, and the risk value, R _j that falls at the j th percentile of the simulated risk distribution (i.e., F=R_d/R_j). The percentile of the simulated risk distribution which corresponds to the deterministic value, R_d , serves as a second measure of compounded conservatism. Analytical results for simple products of lognormal distributions are presented. In addition, a numerical treatment of several complex cases is presented using five simulation analyses from the literature to illustrate. Overall, there are cases in which conservatism compounds dramatically for deterministic point estimates of risk constructed from upper percentiles of input parameters, as well as those for which the effect is less notable. The analytical and numerical techniques discussed are intended to help analysts explore the factors that influence the magnitude of compounding conservatism in specific cases.     

Children and young people requiring home assisted ventilation in the South of England: incidence,receipt of care support and components of the care package

The study found an increasing number of ventilator dependent children and young people living at home. Almost three quarters of the sample had a physical disability as a result of or in addition to their primary diagnosis. There was wide variation in the amount of paid care supporting these families which appeared unrelated to the level of ventilatory dependence. Nurses working in community children's teams or hospital outreach teams were the most frequent care organisers and care managers. The majority of the care packages were funded by Health Authorities.     

Asylum and migration: A review of Home Office statistics

Asylum applications to the UK have been a headline-grabbing topic. Against a background of much criticism in the media of its handling of the statistics, the Home Office asked the National Audit Office (NAO) in April 2004 to examine the reliability of its quarterly asylum statistics. Alison Langham reports on the NAO's work.     

Women with Disabilities: Abortion and Liberation

In this, the United Nations Decade of the Disabled, much is being done to improve the lives of those with disabilities, and to enable them to participate as equals in the everyday life of their communities.

At the same time, however, more and more technological 'advances' are being deployed to detect handicap in the unborn, with the aim of killing as many of them as possible before birth.

Feminists, though accustomed to fighting for the emancipation of women, are failing to address this incongruous situation, and the double discrimination faced by women with disabilities. This is partly due to the fact that they tend to regard abortion as an unequivocal 'right'.

I will argue that far from being a right, abortion underlines women's oppression and is counter-productive to women in general, and to disabled women in particular.     

Comparison of the Rapid Entire Body Assessment and the New Zealand Manual Handling 'Hazard Control Record', for assessment of manual handling hazards in the supermarket industry

This is a case study comparing the use of two different assessment tools (Rapid Entire Body Assessment versus New Zealand Manual Handling Hazard Control Record) to assess, plan and implement changes in manual handling practices in the supermarket industry. Existing manual handling practices being used within these supermarkets were assessed using each of these tools. The most hazardous tasks were revised to improve work methods and reviewed again using both tools, to determine the usefulness and effectiveness of these tools. The process generated considerable discussion regarding the benefits and drawbacks of each tool. The usefulness of each tool appears dependant on the reason for assessment and the anticipated outcome. REBA may be more useful if specific ergonomic or biomechanical changes are being implemented to decrease risk of work-related injury (particularly if an objective numeric score is required for re-assessment following modifications, to determine their effectiveness). The New Zealand Code of Practice for Manual Handling 'Hazard Control Record' Risk Score analysis process lacks specificity and objectivity, however it is less reductionistic and takes into account many factors other than biomechanics and ergonomics. It directs the user toward implementing controls, which are thorough, multi-factorial and useful to control hazards relating to several other areas, including task, load, environment, people and management factors.     

The impact of family structure transitions on youth achievement: Evidence from the children of the NlSY79

We investigated the sensitivity of measures of cognitive ability and socioemotional development to changes in parents' marital status using data from the National Longitudinal Survey of Youth, 1979. We used several scores for each assessment, taken at different times relative to parents' marital transitions, which allowed us to trace the effects starting up to five years before a parent's change in marital status and continuing for up to six years afterward. It also allowed us to correct for the unobserved heterogeneity of the transition and nontransition samples by controlling for the child's fixed effect in estimating the time path of his or her response to the transition. We found that children from families with both biological parents scored significantly better on the BPI and the PIAT-math and PIAT-reading assessments than did children from nonintact families. However, much of the difference disappeared when we controlled for background variables. Furthermore, when we controlled for child fixed effects, we did not find significant longitudinal variation in these scores over long periods that encompass the marital transition. This finding suggests that most of the variation is due to cross-sectional differences and is not a result of marital transitions per se.