Confidence Intervals for the Risk Ratio in Cohort Studies under Inverse Sampling

Three simple interval estimates for the risk ratio in inverse sampling are considered. The first two interval estimates are derived on the basis of Fieller's Theorem and the delta method with the logarithmic transformation, respectively. The third interval estimate is derived on the basis of an F-test statistic proposed by BENNETT (1981) for testing equal probabilities of a disease between two comparison groups when the disease is rare. To evaluate the performance of these three methods, a Monte Carlo simulation is used to compare the actual coverage probability with the nominal confidence level for each method and to estimate the expected length of the corresponding confidence interval in a variety of situations. On the basis of the results found in the simulation, we have concluded that the method with the logarithmic transformation is either equivalent to or better than the other two methods for all situations considered here.     

The role a botanical institute can play in the conservation of the terrestrial biodiversity in a developing country

The need to integratein situ conservation into the planning process is outlined, and the importance of vegetation survey to determine conservation priorities and to identify areas suitable forin situ conservation is stressed. A case is presented, drawing on experience gained in Zimbabwe, of how a botanical institute can become an integral part of biological conservation. The institute should consist of a herbarium, a botanical garden, a gene bank and a vegetation survey unit. The function of each section, how they interlink, and how they can be integrated are discussed.     

Integrated planning and management of freshwater habitats,including wetlands

Freshwater habitats play a very important role in sustaining human activities. Natural functions of wetlands, and other freshwater habitats, generate a wide array of resources that directly or indirectly support the economic and social welfare of diverse groups of people. This role is being seriously weakened as a result of inappropriate planning and management approaches which fail to maintain the functional integrity of the freshwater ecosystems with the result that the flow and quality of resources is degraded. This paper illustrates some of the major functions of wetlands and presents a case for developing integrated planning and management practices that protect the health and productivity of freshwater wetlands and seek to optimise the sustainable use of the flows of resources they generate.     

Planning oral health care for the elderly in Israel for the years 2000 and 2025

The methodology and conclusions of this workshop arc reported here because the problems requiring solution are not unique to Israel. They will increasingly have wide geographical and political application. The population of Israel since its establishment in 1948 has increased about sixfold. The numbers of the elderly (65+) have increased about tenfold. The current situation must be examined and estimates obtained for the next ten years. Only thus can the system be enabled to cope with the problem as it develops. The chosen method was a carefully preplanned, multisectorial workshop. Recommendations were discussed, amended and finalised. The recommendations of the workshop included: Baseline national data is urgently required. Guidelines are required for selecting specific target populations to which priority should be given. The current favourable situation of adequate oral health manpower in Israel makes it possible to encourage providers of oral health care towards treatment for the elderly. It is essential that the appropriate health authorities allocate sufficient funds for the following urgent purposes: the conduct of a national survey of the elderly population; the establishment of oral health units on a trial basis in some selected hospitals; support institutions of higher education to facilitate training in geriatric dentistry. Conclusions. The workshop was multidisciplinary because it was necessary to include all the expertise and experience available as vital elements of the policy making process. This type of workshop was found to be an effective tool for planning oral health services.     

Distributions of the use frequencies of amino acids in the hypervariable regions of immunoglobulins

Two types of distributions for the frequencies of occurrence of amino acids in each position of hypervariable regions CDR-1 and CDR-2 were obtained for 2,000 immunoglobulins. The results show that some positions fit an inverse power-law distribution, while others fit an exponential-type distribution. As a result of comparison with structural data in the literature it is proposed that sites in which the frequency distribution fits the inverse power law are critical to maintaining canonical shapes of the recognition regions or are involved in modulating these canonical conformations, while those sites where the distribution fits the exponential law are those which should be exclusively involved in the recognition mechanism. Correspondence to: F. Lara-Ochoa     

Irrigation planning to transform subsistence agriculture: Lessons From El Salvador

Experience with irrigation schemes designed to improve the productivity of subsistence farmers in Latin America seems to parallel the results of the green revolution in Southeast Asia. Although in some cases the impact on the productivity has been significant, in far too many cases the pervasive pattern of inequity has been reinforced. This case study of the Irrigation District of Zapotitan in El Salvador analyses some of the reasons for the unexpected results, with particular reference to the planning process. It essentially illustrates that the transformation of subsistence agriculture through irrigation demands new institutions designed not only to service agricultural production but also to ensure the accrual of benefits on the targeted group.     

Toward the brave new zoo: Species program planning for reproductive technology development

This article outlines some of the advantages inherent in domestic animal reproductive technology development and compares them to the disadvantages in such development in wildlife species. Species program planning (as proposed by the American Association of Zoological Parks and Aquariums' Species Survival Plan) is offered as an important first step in organizing appropriate research toward reproductive technology development in wildlife species.     

Low hydration phase properties of phospholipid mixtures

An experimental investigation of the low hydration phase properties of phospholipid mixtures is described. ²H (D₂O) NMR, X-ray diffraction and differential scanning calorimetry have been used to elucidate the phase properties of mixtures of the mixed chain phospholipids palmitoyloleoylphosphatidylcholine (POPC) and palmitoyloleoylphosphatidylethanolamine (POPE). At 10% hydration pure POPE exhibited a H_II phase above 330 K, a fluid lamellar phase below 315 K, and a minimally hydrated crystalline phase below 300 K. For the 1:1 mixture, the samples exhibited only gel or fluid phases between 270 K and 360 K for hydrations in the range 15% to 30%. Below 15% hydration the mixture exhibited two fluid phases with different repeat spacings, as predicted previously.