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Pleural Plaques and Their Effect on Lung FunctionConclusions Based on Insufficient Power: Conclusions Based on Insufficient Power to Reject the Null FREE TO VIEW

Curtis W. Noonan, PhD
Author and Funding Information

From the Center for Environmental Health Sciences, University of Montana.

CORRESPONDENCE TO: Curtis W. Noonan, PhD, Center for Environmental Health Sciences, University of Montana, 32 Campus Dr, Missoula, MT 59812; e-mail: curtis.noonan@umontana.edu


FINANCIAL/NONFINANCIAL DISCLOSURES: The author has reported to CHEST that no potential conflicts of interest exist with any companies/organizations whose products or services may be discussed in this article.

FUNDING/SUPPORT: Dr Noonan receives research support from the Libby Epidemiology Research Project funded by the Agency for Toxic Substances and Disease Registry/Centers for Disease Control and Prevention [Grant TS000099-01].

Reproduction of this article is prohibited without written permission from the American College of Chest Physicians. See online for more details.


Chest. 2015;147(3):e124. doi:10.1378/chest.14-2651
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Published online
To the Editor:

I read with interest the article in CHEST (September 2014) by Clark et al1 evaluating pulmonary function measures with respect to pulmonary CT scan findings among former vermiculite workers who were exposed to amphibole fibers. The study shows no statistically significant differences in lung function parameters between the pleural plaques only (PPO) group and the normal CT scan (NCTS) group. The authors indicate confidence “that the potential for type 2 error was minimal.”1 Determination of whether differences between independent groups can be statistically detected (ie, avoiding false negatives) depends upon the sample size, the true difference between groups, and the within-group SD. The mean percentage point difference between PPO and NCTS is 5.29, 5.72, 4.14, and 5.98 for FVC, FEV1, total lung capacity, and diffusing capacity of the lung for carbon monoxide, respectively. Based on the within-group SDs, a control to case ratio of 0.18, and an α level of 0.05, the given sample sizes for PPO and NCTS indicate that this study had only 15% to 34% power to detect the differences noted previously. This post hoc power analysis is limited to the data available in the published tables, and it could be further informed by the covariates in the model. Nevertheless, 80% is typically considered to be a minimal level of power necessary to avoid excess type 2 error.

The authors should be commended for attempting to determine if there are lung function parameter differences according to severity of pleural plaque findings. However, the statistical power problem indicated here is even more severe with the smaller group sizes. The monotonic response by severity status for FVC, FEV1, and residual volume suggests that an evaluation of trend or slope by subgroups may have been valuable. The authors also could have compared each of these PPO subgroups to the NCTS group to yield a more informative, albeit less statistically powerful, comparison.

Finally, for an occupational study, the exposure assessment was limited. Although the authors were able to adjust their models for length of employment and time since last occupational exposure, they do not account for variance in exposure potential according to job task and time period of employment. As noted in prior studies, this occupational cohort experienced a wide range of exposure potentials, and the amphibole exposure histories of workers who had resided locally are further complicated by environmental pathways.2,3 For these reasons, the conclusions by Clark et al1 should be interpreted with caution.

Acknowledgments

Role of sponsors: The sponsor had no role in the design of the study, the collection and analysis of the data, or the preparation of the manuscript.

Clark KA, Flynn JJ III, Goodman JE, Zu K, Karmaus WJJ, Mohr LC. Pleural plaques and their effect on lung function in Libby vermiculite miners. Chest. 2014;146(3):786-794. [CrossRef] [PubMed]
 
Larson TC, Meyer CA, Kapil V, et al. Workers with Libby amphibole exposure: retrospective identification and progression of radiographic changes. Radiology. 2010;255(3):924-933. [CrossRef] [PubMed]
 
Noonan CW, Conway K, Landguth EL, et al. Multiple pathway asbestos exposure assessment for a Superfund community. J Expo Sci Environ Epidemiol. 2015;25(1):18-25. [CrossRef] [PubMed]
 

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References

Clark KA, Flynn JJ III, Goodman JE, Zu K, Karmaus WJJ, Mohr LC. Pleural plaques and their effect on lung function in Libby vermiculite miners. Chest. 2014;146(3):786-794. [CrossRef] [PubMed]
 
Larson TC, Meyer CA, Kapil V, et al. Workers with Libby amphibole exposure: retrospective identification and progression of radiographic changes. Radiology. 2010;255(3):924-933. [CrossRef] [PubMed]
 
Noonan CW, Conway K, Landguth EL, et al. Multiple pathway asbestos exposure assessment for a Superfund community. J Expo Sci Environ Epidemiol. 2015;25(1):18-25. [CrossRef] [PubMed]
 
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