Showing papers by "University of Oxford published in 1976"

Equilibrium in Competitive Insurance Markets: An Essay on the Economics of Imperfect Information

Abstract: Economic theorists traditionally banish discussions of information to footnotes. Serious consideration of costs of communication, imperfect knowledge, and the like would, it is believed, complicate without informing. This paper, which analyzes competitive markets in which the characteristics of the commodities exchanged are not fully known to at least one of the parties to the transaction, suggests that this comforting myth is false. Some of the most important conclusions of economic theory are not robust to considerations of imperfect information.

Design and analysis of randomized clinical trials requiring prolonged observation of each patient. I. Introduction and design.

Abstract: The Medical Research Council has for some years encouraged collaborative clinical trials in leukaemia and other cancers, reporting the results in the medical literature. One unreported result which deserves such publication is the development of the expertise to design and analyse such trials. This report was prepared by a group of British and American statisticians, but it is intended for people without any statistical expertise. Part I, which appears in this issue, discusses the design of such trials; Part II, which will appear separately in the January 1977 issue of the Journal, gives full instructions for the statistical analysis of such trials by means of life tables and the logrank test, including a worked example, and discusses the interpretation of trial results, including brief reports of 2 particular trials. Both parts of this report are relevant to all clinical trials which study time to death, and wound be equally relevant to clinical trials which study time to other particular classes of untoward event: first stroke, perhaps, or first relapse, metastasis, disease recurrence, thrombosis, transplant rejection, or death from a particular cause. Part I, in this issue, collects together ideas that have mostly already appeared in the medical literature, but Part II, next month, is the first simple account yet published for non-statistical physicians of how to analyse efficiently data from clinical trials of survival duration. Such trials include the majority of all clinical trials of cancer therapy; in cancer trials,however, it may be preferable to use these statistical methods to study time to local recurrence of tumour, or to study time to detectable metastatic spread, in addition to studying total survival. Solid tumours can be staged at diagnosis; if this, or any other available information in some other disease is an important determinant of outcome, it can be used to make the overall logrank test for the whole heterogeneous trial population more sensitive, and more intuitively satisfactory, for it will then only be necessary to compare like with like, and not, by chance, Stage I with Stage III.

The Empirical Distribution Function with Arbitrarily Grouped, Censored, and Truncated Data

Abstract: SUMMARY This paper is concerned with the non-parametric estimation of a distribution function F, when the data are incomplete due to grouping, censoring and/or truncation. Using the idea of self-consistency, a simple algorithm is constructed and shown to converge monotonically to yield a maximum likelihood estimate of F. An application to hypothesis testing is indicated.

Gaze and mutual gaze

Abstract: One of the first psychologists to investigate experimentally the role of gaze in human behaviour was Michael Argyle. In 1963 he set up a research group at Oxford with Ted Crossman and Adam Kendon, to study non-verbal communication in human social interaction, which included gaze as an important aspect of this behaviour. Shortly afterwards, Mark Cook joined this group which was funded until 1975, during which time considerable research on gaze had been carried out both at Oxford and elsewhere. This book summarises much of the work done in this field up until that time.

Data Types as Lattices

Abstract: The meaning of many kinds of expressions in programming languages can be taken as elements of certain spaces of “partial” objects. In this report these spaces are modeled in one universal domain ${...

Stability of microstructure in metallic systems

Abstract: Preface Preface to Second Edition 1. The general problem of the stability of microstructure 2. Structural instability due to chemical free energy 3. Highly metastable alloys 4. Instability due to strain energy 5. Microstructural instability due to interfaces 6. Other causes of microstructural instability Index.

Nonlinear gravitons and curved twistor theory

Abstract: A new approach to the quantization of general relativity is suggested in which a state consisting of just one graviton can be described, but in a way which involves both the curvature and nonlinearities of Einstein's theory. It is felt that this approach can be justified solely on its own merits, but it also receives striking encouragement from another direction: a surprising mathematical result enables one to construct the general such nonlinear gravitation state from a curved twistor space, the construction being given in terms of one arbitrary holomorphic function of three complex variables. In this way, the approach fits naturally into the general twistor program for the description of quantized fields.

A derivation of equations for wave propagation in water of variable depth

Abstract: Within the scope of the three-dimensional theory of homogeneous incompressible inviscid fluids, this paper contains a derivation of a system of equations for propagation of waves in water of variable depth. The derivation is effected by means of the incompressibility condition, the energy equation, the invariance requirements under superposed rigid-body motions, together with a single approximation for the (three-dimensional) velocity field.

A derivation of equations for wave propagation in water of variable depth

Abstract: Within the scope of the three-dimensional theory of homogeneous incompressible inviscid fluids, this paper contains a derivation of a system of equations for propagation of waves in water of variable depth. The derivation is effected by means of the incompressibility condition, the energy equation, the invariance requirements under superposed rigid-body motions, together with a single approximation for the (three-dimensional) velocity field.

Parental investment, mate desertion and a fallacy.

Abstract: TRIVERS1 defines parental investment as “any investment by the parent in an individual offspring that increases the offspring's chance of surviving … at the cost of the parent's ability to invest in other offspring”. He has cleverly used this definition to elucidate many outstanding problems in social ethology1–3. But one of his most appealing usages of it is fallacious.

Gonadotropin-releasing hormone surge in pro-oestrous rats

Abstract: IT has generally been accepted that the pre-ovulatory surge of luteinising hormone (LH) is caused by an increased release of gonadotropin-releasing hormone (GnRH) from nerve terminals in the median eminence. So far, however, estimations of the concentrations of GnRH in hypophyseal portal vessel blood by bioassay1 or radioimmunoassay2,3 have failed to demonstrate a surge of GnRH before or during the spontaneous surge of LH. The anaesthetics used (urethane1,3 and sodium pento-barbitone2) block ovulation, and, therefore, are likely to block or truncate a surge of GnRH, if it occurs. We have re-examined this problem using Althesin (Glaxo, Middlesex) an anaesthetic which consists of 9 mg alphaxalone (3α-hydroxy-5α-pregnane-11,20-dione) and 3 mg alphadolone acetate (21-acetoxy-3α-ydroxy-5α-pregnane-11,20-dione) per ml of isotonic aqueous vehicle and show that it does not block the spontaneous LH surge or ovulation. Previous studies on the cat4 suggested that, although it can provide adequate analgesia, Althesin does not interfere with various forebrain functions.

A long-term follow-up study of women using different methods of contraception--an interim report.

Abstract: In 1968, a prospective study was started in collaboration with the Family Planning Association to try to provide a balanced view of the beneficial and harmful effects of different methods of contraception. This investigation is now in progress at seventeen clinics and over 17,000 women are under observation. At the time of recruitment, all these women were married white British subjects, aged 25–39 years, who voluntarily agreed to participate. Fifty-six per cent were using oral contraceptives, 25% were using a diaphragm and 19% were using an intrauterine device (IUD). During follow-up each woman is questioned at return visits to the clinic and a record of pregnancies and their outcome, hospital referrals (inpatient or outpatient), changes in contraceptive methods and the results of cervical smears, is accumulated. Women who default are sent a postal questionnaire and, if this is not returned, are telephoned or visited in their homes to collect the necessary information.So far, data obtained during 56,000 woman-years of observation are available for analysis. Follow-up has been maintained with an annual lapse rate of about 0.3%due to withdrawal of co-operation or loss of contact; adherence to the method of contraception in use at recruitment has been reasonably good, and the reporting of pregnancies and hospital admissions appears to have been both reliable and unbiased.The present data include only 24 deaths, so the mortality associated with different contraceptive methods cannot yet be estimated. With regard to morbidity, however, our preliminary results closely resemble those obtained in the prospective study carried out by the Royal College of General Practitioners (1974) and in the principal retrospective studies carried out in Britain and the United States. Women who used oral contraceptives at the start of the study experienced a deficiency of hospital referrals for cancer, benign lesions of the breast, menstrual disorders other than amenorrhoea, duodenal ulcer, and retention cysts of the ovary; they showed an excess of referrals for cerebrovascular disease, cervical erosion, skin disorders, self-poisoning, migraine, venous thrombosis and embolism, hayfever, gallbladder disease, amenorrhoea, and sterility. Women who used a diaphragm showed a deficiency of hospital referrals for carcinoma-in-situ and dysplastic lesions of the cervix uteri and accidental injury; and an excess of referrals for haemorrhoids and cystitis. Women who used an IUD experienced an excess of hospital referrals for anaemia, varicose veins and salpingitis. About half of these differences (12 out of 23) were predicted from other studies while some suggestive evidence already existed for a further five. Of the remaining six, some probably reflect the influence of selective factors or chance.Multiple pregnancies, stillbirths, malformations, the sex ratio and birthweight showed no consistent relationship to method of contraception. The outcome of unplanned pregnancies occurring in women using an IUD, however, was remarkably unfavourable both in terms of ectopic gestation and miscarriage.Clear evidence was found of impairment of fertility after discontinuation of oral contraceptives. Whether this is likely to lead to permanent sterility in some women is uncertain.The study has provided data on the efficacy of a wide variety of contraceptive methods. In general the failure rates are in keeping with those obtained in other large-scale studies, save that those for the diaphragm and the sheath are much lower than those usually quoted.The available evidence does not yet allow a final balance to be struck between the benefits and risks associated with the new methods of contraception that have become widely used during the last two decades. It seems clear, however, that there are no material risks associated with the use of the diaphragm apart from the risk of pregnancy and that there may be some unintended benefits.

Activities of citrate synthase and NAD+-linked and NADP+-linked isocitrate dehydrogenase in muscle from vertebrates and invertebrates.

Abstract: 1. The activities of citrate synthase, NAD+-linked and NADP+-linked isocitrate dehydrogenase were measured in muscles from a large number of animals, in order to provide some indication of the importance of the citric acid cycle in these muscles. According to the differences in enzyme activities, the muscles can be divided into three classes. First, in a number of both vertebrate and invertebrate muscles, the activities of all three enzymes are very low. It is suggested that either the muscles use energy at a very low rate or they rely largely on anaerobic glycolysis for higher rates of energy formation. Second, most insect flight muscles contain high activities of citrate synthase and NAD+-linked isocitrate dehydrogenase, but the activities of the NADP+-linked enzyme are very low. The high activities indicate the dependence of insect flight on energy generated via the citric acid cycle. The flight muscles of the beetles investigated contain high activities of both isocitrate dehydrogenases. Third, other muscles of both vertebrates and invertebrates contain high activities of citrate synthase and NADP+-liniked isocitrate dehydrogenase. Many, if not all, of these muscles are capable of sustained periods of mechanical activity (e.g. heart muscle, pectoral muscles of some birds). Consequently, to support this activity fuel must be supplied continually to the muscle via the circulatory system which, in most animals, also transports oxygen so that energy can be generated by complete oxidation of the fuel. It is suggested that the low activities of NAD+-linked isocitrate dehydrogenase in these muscles may be involved in oxidation of isocitrate in the cycle when the muscles are at rest. 2. A comparison of the maximal activities of the enzymes with the maximal flux through the cycle suggests that, in insect flight muscle, NAD+-linked isocitrate dehydrogenase catalyses a non-equilibrium reaction and citrate synthease catalyses a near-equilibrium reaction. In other muscles, the enzyme-activity data suggest that both citrate synthase and the isocitrate dehydrogenase reactions are near-equilibrium.

Any Space-Time has a Plane Wave as a Limit

Abstract: It is a great pleasure for me to honour Andre Lichnerowicz on his 60th birthday. And since he has done so much to make relativity respectable as a branch of mathematics, I feel it is appropriate here to point out a simple, yet perhaps surprising, general mathematical property of hyperbolic normal pseudo-Riemannian manifolds which is motivated from knowledge of certain well-known exact solutions in general relativity.

Subunit composition and structure of subcomponent C1q of the first component of human complement.

Abstract: 1. Unreduced human subcomponent C1q was shown by electrophoresis on polyacrylamide gels run in the presence of sodium dodecyl sulphate to be composed of two types of non-covalently linked subunits of apparent mol.wts. 69 000 and 54 000. The ratio of the two subunits was markedly affected by the ionic strength of the applied sample. At a low ionic strength of applied sample, which gave the optimum value for the 54 000-apparent mol.wt. subunit, a ratio of 1.99:1.00 was obtained for the ratio of the 69 000-apparent mol.wt. subunit to the 5400-apparent-mol.wt. subunit. The amount of the 54 000-apparent-mol.wt. subunit detected in the expected position on the gel was found to be inversely proportional to increases in the ionic strength of the applled sample. 2. Human subcomponent C1q on reduction and alkylation, or oxidation, yields equimolar amounts of three chains designated A, B and C [Reid et al. (1972) Biochem. J. 130, 749-763]. The results obtained by Yonemasu & Stroud [(1972) Immunochemistry 9, 545-554], which showed that the 69 000-apparent-mol.wt. subunit was a disulphide-linked dimer of the A and B chains and that the 54 000-apparent-mol.wt. subunit was a disulphide-linked dimer of the C chain, were confirmed. 3. Gel filtration on Sephadex G-200 in 6.0M-guanidinium chloride showed that both types of unreduced subunit were eluted together as a single symmetrical peak of apparent mol.wt. 49 000-50 000 when globular proteins were used as markers. The molecular weights of the oxidized or reduced A, B and C chains have been shown previously to be very similar all being in the range 23 000-24 000 [Reid et al. (1972) Biochem. J. 130, 749-763; Reid (1974) Biochem. J. 141, 189-203]. 4. It is proposed that subcomponent C1q (mol.wt. 410000) is composed of nine non-covalently linked subunits, i.e. six A-B dimers and three C-C dimers. 5. A structure for subcomponent C1q is proposed and is based on the assumption that the collagen-like regions of 78 residues in each of the A, B and C chains are combined to form a triple-helical structure of the same type as is found in collagens.

Differing emotional response from right and left hemispheres

Abstract: To study what might be called the ‘emotional vision’ of the right and left hemispheres of the human brain, a specially designed contact lens was used to show cine films to the right or left hemisphere only. Films were chosen to provoke different kinds of emotional response. We wished to find whether the two hemispheres would take and utilise the stimulus of the film to generate a different emotional response despite the common input. In recent years clinical and experimental data have supported the hypothesis that different emotional reactions follow damage to the right or the left hemisphere1–5. We report here the first part of an investigation in which films were perceived by different hemispheres in normal subjects and the subjects were then asked to judge and rate the films. There is of course no intention of suggesting that information implanted at one hemisphere cannot be transferred to the other6,7; nevertheless, the basis of this research is that the two hemispheres can differ in their vision of the world and that each in some respects formulates its own separate and distinct emotional vision of what it sees. We seek to answer the question of what visual experience is like when that which the subject sees enters his nervous system on only one half of his brain, but this is part of the much wider question of how the two hemispheres of the brain see the world and of the relationship between the two visual halves of the brain.