Causes of Coal Workers' Pneumoconiosis (CWP)
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- Collection of Data
A.1. What were the objectives of the study? What was the association of interest?
The objectives of the study were to examine the association of the prevalence of coal workers' pneumoconiosis (CWP) in the USA and different contributing factors such as level of dust exposure, mine size, low seam mining and other factors. Also the regional differences in CWP were compared. The association of interest is between CWP and various contributing factors and also between different MSHA district regions. It was a cross-sectional study.
A.2. What was the primary outcome (usually a disease, health condition, or other dependent variable) of interest? Briefly explain how the outcome was measured.
The primary outcomes were observed and predicted prevalence in CWP prevalence in miners who participated in this study. Attfield and Morring Exposure response model was utilized to measure the predicted prevalence in CWP and the Chi-square test was used to compare the predicted and observed prevalences in CWP in miners. Radiographs were used to determine the presence of lung parenchymal abnormalities that are consistent with pneumoconiosis obtained from CWHSP.
A.3. What was the primary exposure (actual exposure such as chemical, other risk factor, or other independent variable) of interest? Briefly explain how exposure was measured.
The primary exposures were level of dust exposure concentration, mine size, tenure, seam height. These data were collected from CWHSP, approved by the NIOSH Human Subjects Review Board. Coal mine dust concentration and seam height data were obtained from MSIS.
A.4. What type of study was conducted (study design)? This was a cross sectional study, which was done with a large number of participants from survey data.
A.5. Describe the process of subject selection. Define the source population for this study, if possible.
The study participants were 12,408 underground coal miners from the MSHA districts. Participation in this CWHSP study were voluntary and study participants were 16 years and older. Due to small number of participants and different type of coal type (anthracite rather than bituminous), MSHA district 1 participants were excluded. The source population was all the underground coal miners in MSHA districts in USA.
A.6. Selection bias: What are possible sources in this study? Examples: in a case-control study, how were the study subjects included? In a cohort study, is there loss to follow-up?
The study participants (underground coal miners) in this CWHSP study were stratified by MSHA
districts. Since stratified analyses are important in this study, the probability of being selected in a specific stratum might be different from another stratum and thus a selection bias might have happened.
A.7. Information bias: What are some of the sources of information (measurement) error, for either the exposure or outcome measurement? Are these differential with respect to the exposure or outcome of interest?
For exposure measurement, the investigators analyzed the self reported tenure in mining to derive the cumulative exposures. Also current exposures were examined for CWP which may not establish temporal relationship due to lack of allowance for lag time.
A.8. Confounding: Did the authors consider potential confounders in the design of the study?
The authors considered the following confounders: miner age and coal rank because the effect of respirable coal mine dust can be modified by the rank of the coal.
B. Analysis of Data
B.1. What methods were used to control confounding? Were these sufficient (as far as you can tell)?
As mentioned in the report the investigators incorporated all of the above mentioned covariates in their exposure-response statistical models to control for confounding. No detailed description is found about controlling the confounders.
B.2. What measure of association (e.g. odds ratio, risk ratio, rate difference, etc.) was reported in the study? Was this appropriate?
The authors reported the prevalence of the CWP and prevalence ratio between different MSHA district regions in this study. Since this is a survey based study, prevalence ratio is appropriate.
B.3. How was the uncertainty of the measure of association (effect of random error or statistical significance) reported in this study? Are the conclusions of the study consistent with the uncertainty of the measure of association?
The authors did not report 95% confidence intervals to report the uncertainty of the measure. However they reported the range of measured dust concentration level, worked hours per miners and tenure median. The prevalence ratio was statistically significant (p<0.05) in terms of measure of association between different MSHA regions.
C. Interpretation of Data
C.1. What was the major result of this study?
Major result of this study was that the authors found a significantly higher prevalence of CWP in central Appalachia (MSHA districts 4-7: mainly southern West Virginia, central and eastern Kentucky,
western Virginia and Tennessee) than the predicted levels (10.1% vs 4.2%). However, the prevalence was significantly lower than predicted levels in other regions (1.6% vs 3.6%).
C.2. How would the interpretation of this result be affected by bias (e.g., selection bias, information bias, or confounding)?
There are some factors that might have contributed to the findings of the study. For example, the workforce in central Appalachia was older than other regions. Also central Appalachia had lower proportions of mines with 200 or more workers. Moreover the average seam height was lower in central Appalachia than other regions. Stratification might have affected the result along with the self reporting of study participants.
C.4. To what larger population may the result of this study be generalized? Justify your restrictions (if any) to the generalization of these results
The result of the study may be generalized to all the coal workers in the USA. It might also be generalized to other parts of the world where the coal miners suffer from similar health effects.
C.5. Did the discussion section adequately address the limitations of the study? Was the final conclusion of the paper a balanced summary of the study findings?
The authors discussed limitations of the study adequately. For example, the use of personal protective equipment was a limitation in this study which might have some effect on the result. Also, silica was not considered in this analysis which is supposed to be an important factor. So, the final conclusion of the paper was a balanced summary of the study findings.
C.6. Given the results of this study and the initial literature review, what would you recommend as the next study or intervention to conduct addressing the exposure-disease relationship evaluated in this study?
A future study could be done considering other important factor like silica dust exposure. Other than survey data, an observational study can be done comparing different levels of exposure at different MSHA districts regions.
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