IMPORTANCELung cancer is the leading cause of cancer-related death in the US.OBJECTIVE To review the evidence on screening for lung cancer with low-dose computed tomography (LDCT) to inform the US Preventive Services Task Force (USPSTF).

-A technique is proposed for estimating the probability distribution of total network travel time, in the light of normal day-to-day variations in the travel demand matrix over a road traffic network. A solution method is proposed, based on a single run of a standard traffic assignment model, which operates in two stages. In stage one, moments of the total travel time distribution are computed by an analytic method, based on the multivariate moments of the link flow vector. In stage two, a flexible family of density functions is fitted to these moments. It is discussed how the resulting distribution may in practice be used to characterise unreliability. Illustrative numerical tests are reported on a simple network, where the method is seen to provide a means for identifying sensitive or vulnerable links, and for examining the impact on network reliability of changes to link capacities. Computational considerations for large networks, and directions for further research, are discussed.1 Corresponding author: dwatling@its.leeds.ac.uk .

When discussing the state of research on poverty and social security in Britain Atkinson (I977) pointed out that, in measuring the prevalence of poverty, attention has been focused upon the proportion of the population with an income below the poverty line. It is well known that as an index of poverty this has serious shortcomings-in particular, it is insensitive to how far below the poverty line the incomes of the poor fall. Alternative indices have been proposed: the United States Social Security Administration introduced the notion of poverty gaps (see Batchelder (I97I)), that is, the aggregate value of the difference between the incomes of the poor and the poverty line, while Sen (I976) has suggested that income inequality among the poor is also an important dimension of poverty. Atkinson (I977) therefore proposed that researchers experiment with a range of indices which incorporate such aspects of poverty, given the possibility that the measurement of poverty may be sensitive to the precise index employed. Beckerman (I979) has shown that the information content of poverty gaps very usefully supplements that provided by the aggregate incidence approach. However, to our knowledge, there has been no attempt in Britain to compute indices which take account of inequality among the poor. In this paper we hope to correct this omission, and in doing so comments will be offered on some proposed methods of incorporating such a consideration. A close examination of these has prompted us to propose two further indices which, although relying on the setting up of an alternative structure for analysing this problem, are firmly based on the approaches favoured in the existing literature. THE ECONOMIC JOURNAL [JUNE

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