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1.  Radiological changes after withdrawal from asbestos exposure 
ABSTRACT A group of 135 ex-employees of the Quebec chrysotile production industry comprising men who were born between 1901 and 1920, who had left the industry between 1950 and 1961, and had been radiographed before leaving, attended in 1972 for a medical examination and further chest radiograph. This report concerns 86 men whose withdrawal film was within 12 months of leaving and who had not been exposed subsequently to asbestos or other fibrogenic dust. Seven separate assessments were made of the paired radiographs, side by side in known temporal order. The assessments were classified as showing 'increse' or 'no change'. In 66 film-pairs from men with two years' employment or longer, at least four assessments were of parenchymal increase in six, of pleural increase in 13, and of both parenchymal and pleural increase in two, total 21 (or 31%). There was similar agreement of no change in 24 pairs (36%), and evidence was equivocal in the remaining 21 pairs. Parenchymal increase was not agreed in any of the 20 film-pairs from men with shorter employment, but pleural increase was seen in four of these men, a proportion similar to that in those exposed longer. We conclude that the parenchymal changes observed after leaving the industry, most of which were 'attacks' rather than 'progression', were attributable to the earlier occupational exposure to chrysotile; there were no important differences in age or smoking habit between those with and without parenchymal change.
PMCID: PMC1008488  PMID: 444438
2.  Assessment of radiological progression of simple pneumoconiosis in individual miners 
Liddell, F. D. K. (1974).British Journal of Industrial Medicine,31, 185-195. Assessment of radiological progression of simple pneumoconiosis in individual miners. The studies reported aimed to determine the best method of assessing radiological progression of simple pneumoconiosis in the individual, so that his progression score could be related to other known information about him. The main concern was with subjects for whom three serial posteroanterior chest radiographs were available at approximately quinquennial intervals.
As in other investigations, the 12-point scale of the National Coal Board elaboration led to markedly lower observer error and variability than did the 4-point International Labour Office classification, without distorting levels of progression.
Side-by-side reading led to substantially lower observer error and variability than did independent reading. Although the levels of progression in side-by-side reading were on average a little lower than in independent reading, the effect varied between readers and sessions, being frequently reversed.
Of the three possible methods of side-by-side assessment, the only one without contraindictions was that in which all three films for each subject were viewed together, and there were some specific indications for this approach. Viewing only the first and last films led to some loss of information; viewing all three possible pairs was very expensive of time, both in organization and in actual reading, and was not entirely consistent (additive); and disguise of temporal order of the films proved impractical.
It is concluded that the method of choice for assessing progression in the individual from serial films at roughly quinquennial intervals is to view all films together in known temporal order, recording into the most detailed classification available.
PMCID: PMC1009583  PMID: 4412101
3.  Mortality of British coal miners in 1961 
Liddell, F. D. K. (1973).Brit. J. industr. Med.,30, 15-24. Mortality of British coal miners in 1961. In an earlier enquiry, a sizeable proportion of deaths officially ascribed to coalmining occupations was shown to have been in men who had worked in the industry but not in jobs specific to coalmining, or who had left the mines and taken up other employment. This led to overstatement of mortality among miners, and particularly among face workers.
A new coding of occupations was introduced in 1960, and the present investigation was concerned with all 5 362 men aged 20 to 64 who died in 1961 and were recorded as having last worked in a coalmining occupation or for the National Coal Board. The occupation at the time of last employment was determined from colliery records or after special enquiry by medical officers of health, and again was found to be at considerable variance with that on the death certificate. `Promotion' into coalmining occupations existed in all coalfields and depended on age at death and year of last appearance at work. `Promotion' to the face was particularly marked; however, more men had been working in the industry than were recorded as in specifically coalmining occupations. The effect of retirement from the coalface to other mining work was investigated.
In occupied miners underground, mortality was less than in all occupied and retired males, substantially so at the face. Miners generally had high rates of deaths from accidents and pneumoconiosis, and low rates for lung cancer. For most other causes, face workers had very low rates, while other underground workers and surface workers had rates below and above the national rates for occupied and retired males. Death rates were higher in Scotland than in the other British coalfields.
PMCID: PMC1009473  PMID: 4685295
4.  Morbidity of British coal miners in 1961-62 
Liddell, F. D. K. (1973). Brit. J. industr. Med.,30, 1-14. Morbidity of British coal miners in 1961-62. The British coal mining population in 1961 is described, in terms of the 29 084men covered in a 5% sample census, by age, type of employment, coalfield, size of community, degree of mechanization, and other factors. Over a quarter of the men were in jobs not considered specific to coalmining, although nearly half of such men were working underground. The Ministry of Pensions and National Insurance provided records of over 34 000 spells of incapacity due to sickness for these men. Miners were found to suffer much more incapacity for work than men in other employment, even in those non-mining tasks considered to be very arduous. Among miners at the face, elsewhere underground, and on the surface, the lowest paid had the highest rate of incapacity. Incapacity from most causes was also found to vary between coalfields and with size of residential community, and to depend on the men's financial responsibilities, category of pneumoconiosis, and depth of working, but not on the degree of mechanization. A relationship was observed between seam height and the incidence of new spells of beat knee.
PMCID: PMC1009472  PMID: 4685296
5.  An elaboration of the I.L.O. classification of simple pneumoconiosis 
Liddell, F. D. K., and Lindars, D. C. (1969).Brit. J. industr. Med.,26, 89-100. An elaboration of the I.L.O. classification of simple pneumoconiosis. Simple pneumoconiosis in chest radiographs presents a continuum of increasing abnormality. Liddell (1963) introduced a 12-point scale obtained by dividing each of the four I.L.O. categories (International Labour Office, 1959) into one central and two marginal zones. In this system, which has come to be known as the N.C.B. elaboration, readers record for each radiograph the I.L.O. category of choice (0, 1, 2 or 3), followed by an adjacent I.L.O. category if that had been seriously considered; otherwise, the same category is repeated. Very clear normals are denoted as 0/-, and `high' category 3 films as 3/4.
This paper reviews the evidence from seven reading trials in which 12 National Coal Board (N.C.B.) film readers have taken part. About 28,000 assessments on a total of well over 2,000 single radiographs have been analysed. (The reading of serial radiographs to assess progression is dealt with elsewhere.)
All readers used the elaboration successfully, but they differed in the extents to which they placed films in central and in marginal zones; they were more consistent when preliminary briefing had been given. Film quality had little influence on the use of the zones, except that 0/- tended to be reserved for films of good quality.
Despite the variation in the use of the zones, marked improvements accrued from the use of the elaboration in both intra- and inter-observer error for all readers, and for films of poor quality as well as for good films. The validity of expressing simple pneumoconiosis prevalence rates in terms of I.L.O. categories derived from N.C.B. elaboration readings was confirmed. Although the exact widths of the zones along the continuum remain to be determined, all the evidence suggests that they represent steadily increasing abnormality.
Thus, the N.C.B. elaboration is a practical procedure which amplifies, but neither distorts nor supplants, the I.L.O. classification. It is reported to be easier to use.
PMCID: PMC1008901  PMID: 5780111
6.  An Experiment in Film Reading 
In a first trial of an experimental classification of simple pneumoconiosis, each observer was asked to record, for each reading, not only the (I.L.O.) category into which he would have placed the radiograph but also whether he had seriously considered placing it in an adjacent category. Three skilled readers took part in the experiment, in which 120 films (consisting of three, taken in 1949, 1952, and 1956, for 40 subjects who had been at one colliery throughout the period) were read independently by each reader on two occasions and, subsequently, in a joint reading session. Despite the element of arbitrariness in the definition of when an alternative category should be recorded, the proportion of films for which alternates were quoted was very similar (just about half) for all three readers.
Complete agreement in the finer classification which is produced with the experimental method of reading was naturally less common than when conventional categorization was considered. However, when account was taken of the extent of the disagreements, both intra-observer error and inter-observer error were found to be considerably reduced in the experimental classification.
In studying the progression of pneumoconiosis in the subjects' films from one survey to another, it was found that there was an apparent understatement of progression when the conventional classification was adopted. This arose because, where both films for one subject were placed in the same (I.L.O.) category, there was a considerable tendency for progression to be indicated by a change in the categorization according to the experimental classification.
PMCID: PMC1038383  PMID: 14072622
7.  Injuries to the Semilunar Cartilages of the Knee in Miners 
Comprehensive records of 957 meniscectomies, over a period of 30 months, were obtained from five hospitals in one of the largest British coalfields. Corresponding records of 1,075 appendicectomies were collected and used as reference. The combined data provided conclusive evidence that the rate of meniscectomy was very much higher among miners than among other men. The proportions of bucket handle cartilage tears, which are a severe handicap to any individual, whether miner or not, and of other tears were very similar for miners and for others, in the various hospitals. This suggests that miners are more likely than others to suffer cartilage damage of any type.
Information was also obtained by interviewing some 200 of the miners on whom meniscectomy had been performed. This included the normal attitude at work, the attitude and activity at the time of the incident leading to the tear of the cartilage, and the mechanism of the first incident. It was clear that cartilage tears were more common in miners who knelt at work although, as often as not, the tear actually occurred when the man was walking.
From an examination of 80 consecutive patients, laxity of the knee joint was shown to result from kneeling at work. This appeared to be the initiating factor in the majority of cartilage tears, because it renders the knee more unstable and the menisci more liable to injury when rotational strains are put on the joint. External rotation of the leg on the knee, combined with abduction, when in an upright posture, appeared to be the major factor in producing tears of the medical cartilage; tears of the lateral cartilage, which were much less frequent, appeared to be caused mainly by internal rotation combined with adduction.
Measures of “good housekeeping” in maintaining better walking surfaces are very likely to reduce the number of knee cartilage injuries, by reducing the risk of stumbling and slipping. They should also reduce the incidence of other knee injuries and ligamentous strain, which between them cause a substantial proportion of mining injuries.
PMCID: PMC1038196  PMID: 13911419
8.  The Effect of Film Quality on Reading Radiographs of Simple Pneumoconiosis in a trial of X-ray sets 
Four chest radiographs (14 in. × 14 in. postero-anterior) for each of 86 coal-miners were taken (in a trial to compare ϰ-ray sets) and assessed by a number of experienced readers for both quality and pneumoconiosis. All films were developed by one technician under standard conditions so that variations in the quality of the films produced for one subject arose because of differences in the sets and in the way they were used by the radiographers taking the films. The data thus obtained allowed a study of film quality to be made (a) in relation to the subject and (b) as it affected the reading of simple pneumoconiosis.
The subjects were selected to include a high proportion whose earlier radiographs showed pneumoconiosis; they were thus substantially older than a normal colliery population.
The assessments of quality were found to be reasonably consistent both between observers and on different occasions for the same observer.
A clear tendency was found for the quality of a film to depend on the subject. Men with no radiological evidence of pneumoconiosis tended to produce films which were assessed as of better quality than those of men with pneumoconiosis, however slight. Among the latter, chest thickness had an important effect on film quality; men with thicker chests produced poorer films. The subject's age did not appear to have any effect on the quality of his film.
Film quality was found to introduce only slight biases into the reading of pneumoconiosis. Individual readers varied considerably so that, although on average the readers tended to overcorrect for technical faults, i.e. to read more abnormality in black films than in good ones, and less in grey, some readers undercorrected slightly.
What little evidence was available did not suggest that poor quality of films introduced any excess variability into film reading.
PMCID: PMC1038146  PMID: 13761945
9.  The Measurement of Occupational Mortality 
In making comparisons of the mortality of different occupational groups, it is essential to allow for differences in the age distributions of the groups. The principle of “standardizing” for age is long established. Each of the two conventional methods, direct and indirect, leads to a “Standardized Mortality Ratio” (S.M.R.) which is a weighted average of the ratios of the death rates, by ages, in the occupation, to the corresponding death rates in some standardizing population. In both methods, very great weight is given to the ratio obtained from the oldest age groups. Previous research has shown that there is serious distortion in the recording of occupations, which is greatest among the oldest age groups; the S.M.R.s based on the conventional methods are thus liable to serious error, as well as to “bias”.
A more recent method, inverse, of particular use when the age distribution of the occupation is unknown, gives more equal weights to the ratios of the death rates for the various age groups. The S.M.R. calculated by it, therefore, generally differs markedly from those obtained by the conventional methods.
In a fourth, apparently new method, the weighting of the ratios of death rates is again more uniform than in the conventional methods; it has the further advantage of being based on the age distribution of the standardizing population rather than that of the occupation itself as is the case with the third, inverse, method. This “new” method of obtaining an S.M.R., for comparing the mortality of the occupational group as a whole, is therefore the one which is least open to objection on logical grounds.
However, each of the four methods, and of two others given in the literature, is an attempt to compare one occupation with some standard in terms of a single index, averaging the ratios of the death rates by ages. Such an index can take no account of the variation between these ratios and since this variation is often very great none of the methods can fail to be misleading in many cases. Further, the standard deviation of each index takes no account of this variation and so can be misleading also.
PMCID: PMC1038060  PMID: 14416788

Results 1-11 (11)