Tuesday, March 22, 2016

Remedial Acryonyms

There are a couple abbreviations used in Table 13 and/or Figure 32 that may need reminders. SMR stands for standardized mortality ratio and compares the death rate of a group in question with that of an age-adjusted population of peers. In this study, for instance, it is seen that the Nones group has an SMR of 1.00. This means it exactly corresponds with the general population data accumulated over many years by the U.S. Bureau of Vital Statistics - just what you might expect from so large a population sample.

You should remember that the SMR has nothing to do with the number of deaths from a particular risk - just the ratio of deaths in, say, nuclear plant workers to (divided by) the number of deaths expected in individuals of similar ages and backgrounds.

LHC stands for Lymphatic and Hematopoietic Cancer, which relates to cancers of the lymph nodes and the formation of blood in the body.

A fifth cancer category was not plotted with the rest of the data in Figure 32: the SMR for mesothelioma. Table 13 indicates that both exposed groups showed more than twice the mortality of the unexposed workers. The report suggests, however, that this high ratio was due to both a low (and therefore statistically inaccurate) number of deaths from this cause, and the exposure of both radiation worker groups to environments laden with amphibole fibers - the imported, dangerous form of asbestos. (Not to be confused with the benign chrysotile variety.)

Table 13
Summary of Mortality


NW>5
NW<5
NNW
CAUSE OF DEATH
“Highs”
“Lows”
“Nones”
All Causes
2,797
1,168
4,453
  SMR
0.76
0.81
1.00
  95% Confidence*
0.73, 0.79
0.76, 0.86
0.97, 1.03
Leukemia
21
4
29
  SMR
0.91
0.42
0.97
  95% Confidence*
0.56, 01.39
0.11, 1.07
0.65, 1.39
LHC
50
13
29
  SMR
0.82
0.53
1.10
  95% Confidence*
0.61, 1.08
0.28, 0.91
0.88, 1.37
Mesothelioma
18
8
10
  SMR
5.49
6.14
2.54
  95% Confidence
3.03, 8.08
2.48, 11.33
1.16, 4.43
Lung Cancer
237
98
306
  SMR
1.07
1.11
1.15
  95% Confidence*
0.94, 1.21
0.90, 1.35
1.02, 1.29

Source: Johns Hopkins Final Report, Health Effects of Low-Level Radiation in Shipyard Workers, June 1991, Table 4.1, p. 344.
*The use of 95% confidence limits is a method to show the range of statistically possible values on either side of the most probable value.


Caption for Figure 32: Summary of Shipyard Workers' Mortality: Health Effects of Low-Level Radiation in Shipyard Workers. DOE Contract Number DE-AC02-79EV10095. The Johns Hopkins University, Department of Epidemiology, Baltimore, Md. Final Report. June, 1991.