Non-response bias in a surveillance program for asbestos-related lung cancer

Our plain-English summary of Non-response bias in a surveillance program for asbestos-related lung cancer, by L. Knoll, M.K. Felten, D. Ackermann, et al (Journal of Occupational Health, 2011).

The study

• Authors: L. Knoll, M.K. Felten, D. Ackermann, T. Kraus
• Journal: Journal of Occupational Health
• Published: 2011;53(1):16-22
• Cited by: 9 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Objectives: In a cohort study non-response might lead to a biased selection of cohort members and may affect the validity and reliability of the study outcome. To detect the possible effects of a non-response bias on study results, we evaluated the reasons for non-participation and the differences of respondents and non-respondents in a health surveillance program for power industry workers, formerly exposed to asbestos.

Methods: A cohort of former power plant workers was formed to participate in an early detection program for lung cancer. We evaluated the results of 1,019 individuals (mean age 66 yr), of which 839 took part in at least one examination, 180 refused to participate or did not respond. To obtain the reasons for non-response, we interviewed the cohort members by telephone or we requested them by mail to complete and return a brief questionnaire. Further sources of information were the communal registration offices and local health offices.

Results: The main reasons for non-participation were refusal (35%), illness (23.3%), death (16.7%) and difficulties with traveling (13.3%). It was impossible to make contact with or obtain an explanation from 11.7%. In a logistic regression model we demonstrated that advanced age and a long travel distance from the study center negatively affected the participation rate (p<0.001). There was no difference between respondents and non-respondents regarding prevalence (p=0.559) and incidence of lung cancer (p=0.882).

Conclusion: We concluded that in our cohort non-participation did not cause a selection bias in terms of lung cancer rates.

In plain English

This study examined who did not take part in a German surveillance program for early detection of lung cancer in former power plant workers exposed to asbestos, and whether their absence biased the results. Between March 2002 and July 2004, 1,019 men from eight power plants (mean age 66) were invited. Of these, 839 attended at least one examination and 180 did not. Among the 180, the main reasons were refusal (35%), illness (23.3%), death (16.7%) and travel difficulties (13.3%), and 11.7% could not be contacted. Leaving out those who had died, non-respondents were older on average (70.3 versus 65.1 years) and lived farther from the study center. Older age and longer distance were linked to not taking part. Lung cancer was recorded in 6 (4%) of 150 non-respondents and 25 (3%) of 839 respondents; these totals combine prevalent cases (3 and 16) and incident cases (3 and 9). Neither prevalence (p=0.559) nor age-adjusted incidence density (p=0.882) differed significantly between the groups. There were too few mesothelioma cases to compare. The authors concluded that non-participation did not cause a selection bias in lung cancer rates in their cohort.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Analysis of non-response (non-participation) within a cohort surveillance program for early detection of asbestos-related lung cancer, with follow-up of all invited members
• Who was studied: 1,019 male former power plant workers (mean age 66) from eight electricity-generating power plants of a major German power provider, invited between March 2002 and July 2004. 839 attended at least one examination and 180 did not. Follow-up ended at the end of July 2006.
• Exposure: Former occupational asbestos exposure (fiber type not specified) during maintenance and repair work in power plants, including demolishing turbine insulation or working as bystanders close to this work. Typical jobs were metalworker, welder, insulator or mechanic, electrician, plant operator or supervisor.
• Main results:
  • Among the 180 non-respondents, reasons were refusal (35%), illness (23.3%), death (16.7%) and transport difficulties (13.3%). 21 (11.7%) could not be contacted.
  • Excluding deceased subjects, the 150 non-respondents were on average 5.2 years older than the 839 respondents (70.3 versus 65.1 years). Their latency period from the start of asbestos exposure was 4.6 years longer (45.9 versus 41.3 years).
  • Respondents' mean distance to the health care center was 18.2 km less than non-respondents' (43.9 versus 62.1 km, p=0.002). Exposure time and smoking habits did not differ significantly between the groups.
  • In multivariate logistic regression, older age (adjusted odds ratio for participation 0.87, 95% CI 0.83 to 0.92, p less than 0.001) and longer travel distance (0.99, 95% CI 0.98 to 0.99, p less than 0.001) were significantly associated with non-response. Exposure period, smoking and period of retirement were not.
  • In total, 6 (4%) lung cancer cases and 2 (1.3%) mesothelioma cases were recorded among the 150 non-respondents, and 25 (3%) lung cancer cases and 6 (0.7%) mesothelioma cases among the 839 respondents.
  • Table 4 splits these totals into prevalence and incidence. For lung cancer there were 3 (2%) prevalent and 3 (2%) incident cases among non-respondents, and 16 (1.9%) prevalent and 9 (1.1%) incident cases among respondents. For mesothelioma there were 1 prevalent and 1 incident case among non-respondents, and 1 prevalent and 5 incident cases among respondents.
  • Lung cancer prevalence (3 non-respondents versus 16 respondents) did not differ significantly between the groups (p=0.559).
  • Lung cancer incidence density was 585 per 100,000 person-years for respondents (9 incident cases) and 863 for non-respondents (3 incident cases). Age-adjusted incidence densities did not differ significantly (p=0.882).
  • 28 of the initial non-respondents (15.6%) attended after a telephone or letter contact (late respondents). They did not differ significantly from non-respondents in age, exposure period, retirement, latency or distance.
  • The response proportion was 82.2% (without late respondents), the cooperation proportion 86.7% and the contact proportion 94.9%.
• The authors' conclusion: The authors concluded that in their cohort, non-participation did not cause a selection bias in terms of lung cancer rates.
• Limitations the authors state:
  • There were too few mesothelioma cases for the incidence comparison.
  • Similar disease rates in the two groups did not seem consistent with the non-respondents' significantly older age, which the authors said calls for an explanation.
  • The authors could not evaluate why respondents chose to participate.
  • The reported diagnoses among non-respondents who were ill or had died were not statistically analyzed because the numbers were small.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Lung cancer.

Medical terms in this study, explained in our Lexicon: Lung Cancer, Cohort Study, Selection Bias.

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