Date Published: December 13, 2018
Publisher: Public Library of Science
Author(s): Sajad Shojaee, Nastaran Hajizadeh, Hadis Najafimehr, Luca Busani, Mohamad Amin Pourhoseingholi, Ahmad Reza Baghestani, Maryam Nasserinejad, Sara Ashtari, Mohammad Reza Zali, Hassan Ashktorab.
Misclassification error is a common problem of cancer registries in developing countries that leads to biased cancer rates. The purpose of this research is to use Bayesian method for correcting misclassification in registered cancer incidence of eighteen provinces in Iran. Incidence data of patients with colorectal cancer were extracted from Iranian annual of national cancer registration reports from 2005 to 2008. A province with proper medical facilities can always be compared to its neighbors. Almost 28% of the misclassification was estimated between the province of East Azarbaijan and West Azarbaijan, 56% between Fars and Hormozgan, 43% between Isfahan and Charmahal and Bakhtyari, 46% between Isfahan and Lorestan, 58% between Razavi Khorasan and North Khorasan, 50% between Razavi Khorasan and South Khorasan, 74% between Razavi Khorasan and Sistan and Balochestan, 43% between Mazandaran and Golestan, 37% between Tehran and Qazvin, 45% between Tehran and Markazi, 42% between Tehran and Qom, 47% between Tehran and Zanjan. Correcting the regional misclassification and obtaining the correct rates of cancer incidence in different regions is necessary for making cancer control and prevention programs and in healthcare resource allocation.
Colorectal cancer (CRC) is the third most common cancer among men (10.0% of the total) and the second in women (9.2% of the total) worldwide. Mortality is lower (694,000 deaths, 8.5% of the total) with more deaths (52%) in the less developed regions of the world, reflecting a poorer survival in these regions . In Iran, CRC is the fourth most common type of cancer (the third most common cancer among females and the fifth among males), which accounts for 8.4% of total cancers in the country [2,3].
Registering of cancer reports is obtainable from different references such as pathologies, hospitals, death certificates and etc. National registration programming of cancer cases from Iranian annual of national cancer registration report is extracted during 2005 to 2008 with software which was created by health ministry, until cancer cases are collected, registered and centralized for the past couple of years and is used for data analyses. Hence all new diagnosed cancer cases in temporary information bank are sent from medical universities to ministry of health periodically. After process of duplicating and coding the recorded cancers based on 10th revision of international coding of disease, this information is registered in permanent information bank and all changes are sent to medical universities on specific duration, until permanent information bank of medical universities is equalized with permanent information bank of health ministry. So each medical university has an observed number of cancer cases and also has an expected coverage of cancer cases that are considered to be 100 per 100000 except 2008 that was 113 per 100000. By dividing the observed number to the expected number of cancer cases, the percent of expected coverage for each province is calculated .
Registered cases of colorectal cancer have been included in the study for all provinces in Iran from 2005 to 2008. ASR of CRC incidence for men was 8.02 per 100,000 population (2255 cases) in 2005, whereas that year for women 7.4 per 100,000 (1801 cases). In over time, ASR of CRC incidence for men reached 12.7 per 100,000 population (3527 cases) in 2008 and for women to 11.12 per 100,000 (2658 cases) in the same year. The trend of CRC from 2005 to 2008 for both sexes is shown in Fig 1.
It is obvious that the neighboring provinces due to the same eating habits, lifestyle and climate, have the same health outcomes . But sometimes when analyzing registered data, it is observed that the neighboring provinces not only have different outcomes but are also inconsistent. This situation implies that there is misclassification in registered data. This problem is a notable matter in medicine which may results in deflecting of health programing and health resources allocation . Such deflection could make irrecoverable damage on national scale. The aim of the present study was to help reducing misclassification error in registered colorectal cancer data in Iran. Firstly, the means in accessing health resources in welfare provinces and secondly the lack of health facilities in their neighboring provinces are elements in creating misclassification error. Fortunately, some studies have been conducted in Iran in order to eliminate the misclassification errors for mortality and morbidity registered cancer data in the case of Liver , Gastric , and colorectal cancers . Applying the results of the studies above may be more reliable, since they had re-estimated and produced valid data. According to the result of our research, there was a non-ignorable estimated misclassification rate among adjacent provinces. The highest estimated misclassification parameter, belongs to North Khorasan, Hormozgan, and Sistan which are in the east and south of Iran. So the real rates of CRC in those provinces are higher than the rates that are reported by cancer registry system.