While pondering a return to deaths caused by nuclear energy, I decided to look at the number of nuclear industry deaths vs. the number of coal mining and coal-burning power plant deaths. Doing this right should involve not only direct deaths (i.e. death by industrial accident) but also indirect deaths from chronic occupational diseases. As I was collecting my data, I spotted a handful of news reports from last Summer claiming a resurgence of black lung disease. Two of those reports were done by NPR, a news outlet I like and usually trust for unbiased news.

NPR reported an "surge" of black lung cases (http://www.npr.org/2012/07/09/155978300/as-mine-protections-fail-black-lung-cases-surge, accessed 3/21/13):

Incidence of the disease that steals the breath of coal miners doubled in the last decade, according to data analyzed by epidemiologist Scott Laney at the National Institute for Occupational Safety and Health (NIOSH).

The NPR report showed the following graphic on their website as support for their statement and cited the National Institute for Occupational Safety and Health ("NIOSH") data (ibid.):


The NPR report along with several other news reports (e.g., http://www.wvgazette.com/News/201207070075, accessed 3/20/13) claim an increase in black lung cases, especially in coal miners with over 25 years experience and in miners with relatively short experience. The upward trend in the bins on the far right of their graphic appears to support this. (Since this data is based on a NIOSH program for screening miners to find black lung symptoms, I'm labeling this as "screened-miner data" in the rest of this post.)

There's a problem here. CDC numbers for black lung incidence have some big data gaps. Here's the raw NIOSH data fresh off of the CDC website (http://www2a.cdc.gov/drds/WorldReportData/FigureTableDetails.asp?FigureTableID=2550&GroupRefNumber=T02-12; accessed 3/20/13):


It is a bit disturbing that in categories with no data, there is a percentage reported. This is a problem since the missing data makes it impossible to test the claim that decadal black lung rates have doubled. There is a possible workaround and that is to use the number of annual black lung deaths. People with advanced-stage black lung do not live long so any increases in the number of new black lung cases should be reflected in the number of black lung deaths. Oddly, this isn't apparent in the death statistics. Here's NIOSH's own graphic for black lung cases by year (http://www2a.cdc.gov/drds/WorldReportData/FigureTableDetails.asp?FigureTableID=2568&GroupRefNumber=F02-01; accessed 3/20/13).:


There is a way to possibly reconcile the news report claims and the actual raw NIOSH data. The news reports look at the percentage of screened miners with black lung symptoms as revealed by chest x-rays, whereas the raw death statistics deal with death only. Because of this, it is possible that a real increase in black lung cases has not yet had time to impact the reported rates of black lung deaths. If this is the case, then there should be an increase in annual black lung deaths in the immediate future.

There is a second possibility to account for the uptick shown in the NPR graph for the most experienced miners. The NPR graph lumps all the screened-miner data into five year averages. Given the obvious wobble in the annual NIOSH death figures, the apparent increase in the screened-miner averaged data could be a statistical fluke. It's an old trick to massage one's numbers when binning by changing the bin size or shifting the bin position. The trends shown on the NPR graph of NIOSH data are not as nice nor as conclusive is one uses a smaller bin size. Any real trend of increasing black lung cases should be as apparent in the annual data (bin size = 1 year) and in the half-decade data (bin size = 5 years). Here's the NIOSH balck lung incidence data plotted by year:


Looking at the black lung rate data on an annual basis shows that there is a lot of variability from year to year. The one period that this is not true is the 1990s where the rates smoothed out. Given the overall variability, it is possible that the hypothesized increase from the 1990s to the 2000s is really the result of data variability. Given the low overall numbers of black lung cases, variability is not at all surprising. This is how a lot of small datasets behave. At this point, one can argue that the 1990s data are the odd man out here due to their lack of variability. Such a hypothesis is equally plausible compared to a claim that black lung cases have doubled. The variability in the annual plot of black lung rates calls the decadal increase in black lung incidence into question. Given the small number of data points and the gaps in the discrete data, the increased black lung incidence rates are a dataset with some troubles.

Another problem with trying to use the screened-miner data is that the screening may not be representative of all miners because NIOSH screening for black lung is voluntary. There is no real control on who gets screened. A further factor involves where NIOSH collected their data. NIOSH offered screening to miners in 16 states; however, NIOSH offered enhanced additional screening to underground miners in just the "hot spot" states of Virginia, West Virginia and Kentucky (http://www.cdc.gov/niosh/topics/surveillance/ords/ecwhsp.html, accessed 3/21/13). This raises the possibility of real bias in the NIOSH screened-miner data both by area and by mine type (underground vs. surface).

Regardless of the decreasing death rate, researchers at NIOSH do believe that the number of black lung cases is increasing (e.g., CDC, Pneumoconiosis and advanced occupational lung disease among surface coal miners--16 states, 2010-2011: MMWR Morb Mortal Wkly Rep. 2012 Jun 15;61(23):431-4); however, even if the black lung rate doubled from the 1990s to 2000s as reported by NPR, that rate would still be an order of magnitude less than rates for 1970s. And this is what NPR labeled as a "surge" in black lung cases. It is worth noting that the news reports appear to have targeted and emphasized the increased number of black lung cases in the youngest and oldest miners when compared to the non-sensational presentation of data on the NIOSH website and in peer-reviewed studies by NIOSH researchers. A quick cruise through recent papers and abstracts on pubmed.gov tells a different story from the news reports. After looking at long-term rates of black lung, the only less-than-trivial increase in black lung disease was in underground miners in Central Appalachia (ibid.). Small underground coal mines were singled out as having five times the rate of black lung compared to large mines, especially in Appalachia. Oddly, x-ray images of surface coal miners showed an unexpected incidence of silicosis along with some observations of black lung. (Laney AS, Attfield MD. (2010) : Coal workers' pneumoconiosis and progressive massive fibrosis are increasingly more prevalent among workers in small underground coal mines in the United States. Occup Environ Med. 2010 Jun;67(6):428-31. doi: 10.1136/oem.2009.050757.) It was the news reports which made a big deal out of the relative increase in black lung cases, not NIOSH.

Frankly, it's a mess. Only time will tell if the black lung death rate catches up with the NIOSH screened-miner black lung symptoms data. Given the problems with the black lung incidence rates, using the death stats as a surrogate has great appeal. The death stats have none of the problems that the rate data have. The virtue of death statistics is their simplicity. There is usually no second-guessing or doubts of biasing with death stats. The screened-miner data is really a mess in comparison. While I'm not completely sure that someone was wrong on the internet, it is more than certain that someone was confusing!

Pushing the data around masks the ongoing tragedy of black lung disease. While an increase in cases for the whole country is debatable, there is data to support that black lung cases in Central Appalachia and in small underground mines really have increased. Black lung disease in this country greatly decreased after 1970 because of the regulation of coal dusts that started in 1969. This is a clear cause and effect relationship between regulation and desired result. If the coal dust regulations are faithfully followed, black lung cases become increasingly rare. The tragedy here is that black lung is one of the truly preventable occupational diseases. Arm waving about data trends and variability will not make the black lung "hot spot" in Appalachia go away - only better enforcement of the coal dust regulations will do that.

You may want to note that the Mining Safety and Health Administration's budget for coal mine inspection and safety enforcement has been steadily cut for the last two decades so enforcement of the coal dust regulations is now uncommon compared to 30 years ago.

Anyone can play with the black lung data compiled by NIOSH at: http://webappa.cdc.gov/ords/cwhsp-database.html (accessed 3/21/13).