Five physicians' radiological assessments of coalworkers' simple pneumoconiosis (CWP) in 2600 coalminers at 10 British collieries have been studied in relation to the individuals' estimated lifetime (mean 33 years) exposure to respirable coalmine dust. Estimates of exposure were based on 20 years of observations at each colliery. Radiographic classifications were clearly associated with the measures of dust exposure. Important unexplained differences between some of the collieries were disclosed. Among men with similar cumulative dust exposures those with longer exposure time had higher prevalence of CWP. In general there was no evidence that the quartz concentrations experienced (average 5 % of mixed dust) affected the probability of developing coalworkers' simple pneumoconiosis. Some men reacted unfavourably (two or more steps of change on the 12-point radiological scale) over a 10-year period to coalmine dust with a relatively high quartz content.Earlier reports from the National Coal Board's Pneumoconiosis Field Research have described an association between exposure to respirable coalmine dust and incidence of coalworkers' simple pneumoconiosis (CWP).1-5 The effect of quartz has also been studied.6 These were interim investigations, based on a 10-year period of observations of coalface workers at 20 British collieries. Results from a longer-term study at 10 collieries are presented in this paper, which has two main objectives. The first is to report new dust-related estimates of long-term incidence risks of pneumoconiosis among working miners. The second is to present further information on how the chances of developing CWP are influenced by the quartz content of the coalmine dust to which men are exposed. SubjectsSince 1953 medical surveys of the Pneumoconiosis Field Research have been carried out at roughly five-year intervals at selected collieries from all the major British coalfields. Ten collieries were surveyed at least five times. They cover a wide range of environmental and geological conditions. All currently employed miners were asked to take part on each occasion. This report considers primarily the 2600 men who attended the first, third, and fifth surveys at the 10 collieries, and for whom complete and reliable data were available. Men no longer in the industry were not studied: 8394 men, examined at these collieries at the first surveys, were alive and under 65 years old 20 years later. The 2600 long-term working miners studied form 31 % of that group. Some results are reported for a further 1730 men who attended the third and fifth surveys, but not the first, at these same collieries. Methods RADIOLOGICAL DATAEach of five physicians experienced in the radiology of pneumoconiosis classified the fifth survey fullsized (posteroanterior) chest radiographs of the men separately, independently, and in random order according to the ILO U/C International Classification of Radiographs of the Pneumoconioses,7 using 1968 standard films. Additionally, the readers classified all 4330 pairs of the third a...

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This paper considers the economic efficiency benefits of urban public transport subsidies and presents estimates of the marginal benefits of fare and service level changes in the main Australian cities. Models to evaluate benefits are outlined, and estimates compared of the benefits to public transport and other road users of fare and service level changes in different cities. A major conclusion is that existing urban public transport subsidies might be more effective from an economic efficiency point of view if frequency levels were reduced and the consequent cost savings used to finance lower levels of fares.