HHS Public Access Author manuscript Author Manuscript
Cancer. Author manuscript; available in PMC 2015 October 15. Published in final edited form as: Cancer. 2014 October 15; 120(20): 3261–3262. doi:10.1002/cncr.28866.
(Letter to the Editor): Limitations in the imputation strategy to handle missing nativity data in SEER Paulo S. Pinheiro, MD PhD, Epidemiology and Biostatistics, University of Nevada Las Vegas, School of Community Health Sciences, (702) 895 5717
Author Manuscript
Timothy J. Bungum, PhD, and Epidemiology and Biostatistics, University of Nevada Las Vegas, School of Community Health Sciences, (702) 895 4986 Hongbin Jin, RN MPH Epidemiology and Biostatistics, University of Nevada Las Vegas, School of Community Health Sciences Paulo S. Pinheiro: [email protected]; Timothy J. Bungum: [email protected]; Hongbin Jin: [email protected]
Abstract
Author Manuscript
The proposed multiple imputation strategy for handling missing nativity data is affected by well established associations between stage at diagnosis, specified ethnicity, known birthplace, and survival.
Dear Editor
Author Manuscript
We recognize the innovative approach of Montealegre et al. in studying cancer disparities between foreign and US-born ethnic minorities.1 In the past, this type of analysis has been plagued by data limitations. Among these, birthplace information collected by cancer registries is incomplete and this deficiency does not occur randomly. This is because birthplace information is often secured from death certificates. In other words, those with a known birthplace are disproportionately deceased while those without birthplace information tend to be cancer survivors.2–5 As such, in this study the stage at diagnosis, and ethnicity subcategory used in the logistic regression model to determine a birth in the US or a foreign birth reflect data disproportionately derived from deceased cases with a known birthplace, while the imputation is performed on a completely different group of patients, mostly cancer survivors. Thus the “missing at random” assumption that allows for the use of multiple imputation here is of complex interpretation. Moreover, the authors then use the results of that imputed birthplace to study survival. However, both stage and Hispanic ethnicity are strongly associated with survival which may raise questions about the validity of this survival analysis.
Correspondence to: Paulo S. Pinheiro, [email protected].
Pinheiro et al.
Page 2
Author Manuscript
In SEER, patients have their birthplace recorded based on the information in their medical records at the time of diagnosis. However, not all the medical records contain this information. When patients die, there is an additional report of birthplace coming from the death certificate. SEER registries will collect this additional information and that is why birthplace data is more complete for deceased than for living cases.
Author Manuscript
SEER requires annual data submissions from all participating registries. These submissions include both newly diagnosed cancer cases, but also updated information (such as birthplace) on cancer cases from the previous submissions. Thus, by analyzing data on two different submissions of SEER data, we can analyze the distributions of nativity for the existing cases at two different points in time. It follows that one can compare the proportions of US-born and foreign-born in a later submission among all cases with unknown birthplace in an earlier submission to the corresponding proportions of nativity obtained from the multiple imputation procedures that Montealegre et al. propose. For this purpose we requested and analyzed a dataset from SEER that was restricted to Hispanic cases diagnosed from 1995–2004, who were reported in two different submissions, the 2006 (earlier submission) and 2012 (later submission). A total of 53,531 cases among Hispanics were reported in both submissions; 5,812 cervical cancers, 28,346 prostate cancer cases and 19,373 colorectal cancer cases. Of these a total of 2,345 (112 cases of cervical cancer, 1,403 cases of prostate cancer and 830 cases of colorectal cancer) had unknown birthplace in the 2006 submission, but their birthplace became available in the 2012 submission; of which 43 cervical cancer, and 534 prostate cancer, and 207 colorectal cancer cases turned out to be foreign-born, respectively.
Author Manuscript
The proportions of unknown birthplaces allocated for foreign-born and US-born cases using Montealegre’s imputation were respectively 12% and 88% for cervical cancer, 14% and 86% for prostate cancer, and 10% and 90% for colorectal cancer. Based on observed data our findings were significantly different. For cervical cancer the observed data showed that 38% were foreign-born and 62% were US-born (95% confidence intervals 30%–48% and 52%–70% respectively). For prostate cancer we found 38% (95%CI 36%–41%) foreign-born and 62% US-born (95%CI: 59%–64%). Finally, for colorectal cancer we determined that 25% (95%CI 22%–28%) were foreignborn and 75% were US-born (95%CI 72%–80%).
Author Manuscript
The 2,345 analyzed cases (unknown birthplace in 2006 but known birthplace in 2012) were significantly older than the remaining cancer cases with an unknown birthplace in both submissions. This was expected given that between the two points in time, older cases are more likely to die and birthplaces will be recovered from the death certificates of deceased subjects. However, in the total group with known birthplace in 2006 and 2012, the foreignborn cases are significantly younger than US-born cancer cases. This suggests that the observed proportions in our analysis are an overestimate of the US-born and an underestimate of the foreign-born, and therefore the differences between the proportions as
Cancer. Author manuscript; available in PMC 2015 October 15.
Pinheiro et al.
Page 3
Author Manuscript
estimated by Montealegre et al and the real proportions are even greater than those reported here. Overall, these results strongly suggest that the proportions of nativity obtained from multiple imputations are significantly overestimated for the US-born and underestimated for the foreign-born, which will produce a bias of unpredictable direction in the reported survival differences between foreign-born and US-born Hispanic populations. Improved methods for addressing the important limitations surrounding nativity data in cancer surveillance are needed.
Acknowledgments Financial disclosures and conflicts of interest: Dr. Pinheiro is sponsored in part by the National Institutes of Health National Institute of Genereal Medical Sciences / NV INBRE (grant 8 P20 GM103440)
Author Manuscript
References
Author Manuscript
1. Montealegre JR, Zhou R, Amirian ES, Scheurer ME. Uncovering nativity disparities in cancer patterns: multiple imputation strategy to handle missing nativity data in Surveillance, epidemiology, and End Results data file. Cancer. 2014 Jan 16. 2. Lin SS, Clarke CA, O’Malley CD, Le GM. Letter to the Editor. Studying cancer incidence and outcomes in immigrants; methodological concerns. Am J Public Health. 2002; 92:1757–1759. [PubMed: 12406802] 3. Pinheiro PS, Bungum TJ. Country of origin and breast cancer survival. Letter to the Editor. Asia Pac J Clin Oncol. 2013 4. Pinheiro PS. The influence of Hispanic ethnicity on non-small cell lung cancer histology and patient survival: an analysis of the Survival, Epidemiology, and End Results database. Letter to the Editor. Cancer. 2013; 119(6):1285–1286. [PubMed: 23027518] 5. Pinheiro PS, Morris CR, Liu L, Bungum TJ, Altekruse SF. The impact of follow-up type and missed deaths on population-based cancer survival studies for Hispanics and Asians. J Natl Cancer Inst Monogr. 2014 in press.
Author Manuscript Cancer. Author manuscript; available in PMC 2015 October 15.
Cancer. Author manuscript; available in PMC 2015 October 15. Published in final edited form as: Cancer. 2014 October 15; 120(20): 3261–3262. doi:10.1002/cncr.28866.
(Letter to the Editor): Limitations in the imputation strategy to handle missing nativity data in SEER Paulo S. Pinheiro, MD PhD, Epidemiology and Biostatistics, University of Nevada Las Vegas, School of Community Health Sciences, (702) 895 5717
Author Manuscript
Timothy J. Bungum, PhD, and Epidemiology and Biostatistics, University of Nevada Las Vegas, School of Community Health Sciences, (702) 895 4986 Hongbin Jin, RN MPH Epidemiology and Biostatistics, University of Nevada Las Vegas, School of Community Health Sciences Paulo S. Pinheiro: [email protected]; Timothy J. Bungum: [email protected]; Hongbin Jin: [email protected]
Abstract
Author Manuscript
The proposed multiple imputation strategy for handling missing nativity data is affected by well established associations between stage at diagnosis, specified ethnicity, known birthplace, and survival.
Dear Editor
Author Manuscript
We recognize the innovative approach of Montealegre et al. in studying cancer disparities between foreign and US-born ethnic minorities.1 In the past, this type of analysis has been plagued by data limitations. Among these, birthplace information collected by cancer registries is incomplete and this deficiency does not occur randomly. This is because birthplace information is often secured from death certificates. In other words, those with a known birthplace are disproportionately deceased while those without birthplace information tend to be cancer survivors.2–5 As such, in this study the stage at diagnosis, and ethnicity subcategory used in the logistic regression model to determine a birth in the US or a foreign birth reflect data disproportionately derived from deceased cases with a known birthplace, while the imputation is performed on a completely different group of patients, mostly cancer survivors. Thus the “missing at random” assumption that allows for the use of multiple imputation here is of complex interpretation. Moreover, the authors then use the results of that imputed birthplace to study survival. However, both stage and Hispanic ethnicity are strongly associated with survival which may raise questions about the validity of this survival analysis.
Correspondence to: Paulo S. Pinheiro, [email protected].
Pinheiro et al.
Page 2
Author Manuscript
In SEER, patients have their birthplace recorded based on the information in their medical records at the time of diagnosis. However, not all the medical records contain this information. When patients die, there is an additional report of birthplace coming from the death certificate. SEER registries will collect this additional information and that is why birthplace data is more complete for deceased than for living cases.
Author Manuscript
SEER requires annual data submissions from all participating registries. These submissions include both newly diagnosed cancer cases, but also updated information (such as birthplace) on cancer cases from the previous submissions. Thus, by analyzing data on two different submissions of SEER data, we can analyze the distributions of nativity for the existing cases at two different points in time. It follows that one can compare the proportions of US-born and foreign-born in a later submission among all cases with unknown birthplace in an earlier submission to the corresponding proportions of nativity obtained from the multiple imputation procedures that Montealegre et al. propose. For this purpose we requested and analyzed a dataset from SEER that was restricted to Hispanic cases diagnosed from 1995–2004, who were reported in two different submissions, the 2006 (earlier submission) and 2012 (later submission). A total of 53,531 cases among Hispanics were reported in both submissions; 5,812 cervical cancers, 28,346 prostate cancer cases and 19,373 colorectal cancer cases. Of these a total of 2,345 (112 cases of cervical cancer, 1,403 cases of prostate cancer and 830 cases of colorectal cancer) had unknown birthplace in the 2006 submission, but their birthplace became available in the 2012 submission; of which 43 cervical cancer, and 534 prostate cancer, and 207 colorectal cancer cases turned out to be foreign-born, respectively.
Author Manuscript
The proportions of unknown birthplaces allocated for foreign-born and US-born cases using Montealegre’s imputation were respectively 12% and 88% for cervical cancer, 14% and 86% for prostate cancer, and 10% and 90% for colorectal cancer. Based on observed data our findings were significantly different. For cervical cancer the observed data showed that 38% were foreign-born and 62% were US-born (95% confidence intervals 30%–48% and 52%–70% respectively). For prostate cancer we found 38% (95%CI 36%–41%) foreign-born and 62% US-born (95%CI: 59%–64%). Finally, for colorectal cancer we determined that 25% (95%CI 22%–28%) were foreignborn and 75% were US-born (95%CI 72%–80%).
Author Manuscript
The 2,345 analyzed cases (unknown birthplace in 2006 but known birthplace in 2012) were significantly older than the remaining cancer cases with an unknown birthplace in both submissions. This was expected given that between the two points in time, older cases are more likely to die and birthplaces will be recovered from the death certificates of deceased subjects. However, in the total group with known birthplace in 2006 and 2012, the foreignborn cases are significantly younger than US-born cancer cases. This suggests that the observed proportions in our analysis are an overestimate of the US-born and an underestimate of the foreign-born, and therefore the differences between the proportions as
Cancer. Author manuscript; available in PMC 2015 October 15.
Pinheiro et al.
Page 3
Author Manuscript
estimated by Montealegre et al and the real proportions are even greater than those reported here. Overall, these results strongly suggest that the proportions of nativity obtained from multiple imputations are significantly overestimated for the US-born and underestimated for the foreign-born, which will produce a bias of unpredictable direction in the reported survival differences between foreign-born and US-born Hispanic populations. Improved methods for addressing the important limitations surrounding nativity data in cancer surveillance are needed.
Acknowledgments Financial disclosures and conflicts of interest: Dr. Pinheiro is sponsored in part by the National Institutes of Health National Institute of Genereal Medical Sciences / NV INBRE (grant 8 P20 GM103440)
Author Manuscript
References
Author Manuscript
1. Montealegre JR, Zhou R, Amirian ES, Scheurer ME. Uncovering nativity disparities in cancer patterns: multiple imputation strategy to handle missing nativity data in Surveillance, epidemiology, and End Results data file. Cancer. 2014 Jan 16. 2. Lin SS, Clarke CA, O’Malley CD, Le GM. Letter to the Editor. Studying cancer incidence and outcomes in immigrants; methodological concerns. Am J Public Health. 2002; 92:1757–1759. [PubMed: 12406802] 3. Pinheiro PS, Bungum TJ. Country of origin and breast cancer survival. Letter to the Editor. Asia Pac J Clin Oncol. 2013 4. Pinheiro PS. The influence of Hispanic ethnicity on non-small cell lung cancer histology and patient survival: an analysis of the Survival, Epidemiology, and End Results database. Letter to the Editor. Cancer. 2013; 119(6):1285–1286. [PubMed: 23027518] 5. Pinheiro PS, Morris CR, Liu L, Bungum TJ, Altekruse SF. The impact of follow-up type and missed deaths on population-based cancer survival studies for Hispanics and Asians. J Natl Cancer Inst Monogr. 2014 in press.
Author Manuscript Cancer. Author manuscript; available in PMC 2015 October 15.
