Area-To-Area Poisson Kriging Analysis of Mapping of County- Level Esophageal Cancer Incidence Rates in Iran

DOI:http://dx.doi.org/10.7314/APJCP.2013.14.1.11 Area-to-Area Poisson Kriging Analysis of County-Level Esophageal Cancer Incidence Rates in Iran

RESEARCH ARTICLE

Area-to-Area Poisson Kriging Analysis of Mapping of County- Level Esophageal Cancer Incidence Rates in Iran

Naeimeh Sadat Asmarian1, Ahmad Ruzitalab2, Kavousi Amir3, Salehi Masoud4, Behzad Mahaki5*

Abstract

Background: Esophagus cancer, the third most common gastrointestinal cancer overall, demonstrates high incidence in parts of Iran. The counties of Iran vary in size, shape and population size. The aim of this study was to account for spatial support with Area-to-Area (ATA) Poisson Kriging to increase precision of parameter estimates and yield correct variance and create maps of disease rates. Materials and Methods: This study involved application/ecology methodology, illustrated using esophagus cancer data recorded by the Ministry of Health and Medical Education (in the Non-infectious Diseases Management Center) of Iran. The analysis focused on the 336 counties over the years 2003-2007. ATA was used for estimating the parameters of the map with SpaceStat and ArcGIS9.3 software for analysing the data and drawing maps. Results: Northern counties of Iran have high risk estimation. The ATA Poisson Kriging approach yielded variance increase in large sparsely populated counties. So, central counties had the most prediction variance. Conclusions: The ATAPoisson kriging approach is recommended for estimating parameters of disease mapping since this method accounts for spatial support and patterns in irregular spatial areas. The results demonstrate that the counties in provinces Ardebil, Mazandaran and Kordestan have higher risk than other counties.

Keywords: Disease mapping - area-to-area Poisson Kriging - esophagus cancer - Iran

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Introduction techniques for the discrete distribution. Kaiser et al. (1997) introduced a spatial Poisson distribution. Oliver et al. Cancer is the third cause of mortality after car (1998) employed binomial cokriging to produce a map of accident and cardiovascular disease in Iran, so cancer is childhood cancer risk in the West Midlands of England. an important problem in public health in Iran. Esophagus Monestiez et al. (2004; 2006) developed Poisson kriging cancer has high incidence in north counties of Iran. The WRPRGHOVSDWLDOO\KHWHURJHQHRXVREVHUYDWLRQLQWKHÀHOG main aim of this study is the Esophagus Cancer mapping of marine ecology. Goovaerts (2005) generalized Poisson for describe geographic of disease risk and identifying kriging to analyse cancer data under the assumption that unusual high risk areas. The counties of Iran vary in size, all geographic units are the same size, then Goovaert shape and population size. (2006) used Area-to-Area Poisson kriging technique for The area data used in this study is count data based on corporate the geometry of administrative units and the the Poisson distribution, so Area-to-Area Poisson kriging spatial repartition of the population at risk. This approach approach has been used for estimating the parameters applied areal supports to predict area values by taking into of the map. Area-to-Area Poisson kriging approach is account the spatial support of data as well as the varying available to account for spatially varying population population size, leading to more precise and accurate sizes and spatial patterns in the mapping of disease rates. estimates of the risk. This approach estimates disease risk more accurately and The case of interest was esophagus cancer patients precisely. Area-to-Area Poisson kriging is a geostatistical registered between the years 2003-2007 and adjusted

1'HSDUWPHQWRI%LRVWDWLVWLFV6FKRRORI3DUDPHGLFLQH3'HSDUWPHQWRI6FLHQFHV6FKRRORI+HDOWK6DIHW\DQG(QYLURQPHQW6KDKLG %HKHVKWL8QLYHUVLW\RI0HGLFDO6FLHQFHV4'HSDUWPHQWRI6WDWLVWLFVDQG0DWKHPDWLFV6FKRRORI+HDOWK0DQDJHPHQWDQG,QIRUPDWLRQ 6FLHQFHV0HPEHURI+HDOWK0DQDJHPHQWDQG(FRQRPLFV5HVHDUFK&HQWHU7HKUDQ8QLYHUVLW\RI0HGLFDO6FLHQFHV7HKUDQ 2'HSDUWPHQWRI$SSOLHG0DWKHPDWLFV6FKRRORI0DWKHPDWLF6FLHQFHV)HUGRZVL8QLYHUVLW\RI0DVKKDG0DVKKDG5'HSDUWPHQW RI%LRVWDWLVWLFV6FKRRORI3XEOLF+HDOWK,VIDKDQ8QLYHUVLW\RI0HGLFDO6FLHQFHV,VIDKDQ,UDQ )RUFRUUHVSRQGHQFHEHK]DG PDKDNL#JPDLOFRP $VLDQ3DFLÀF-RXUQDORI&DQFHU3UHYHQWLRQ9RO 11 Naeimeh Sadat Asmarian et al _ using the 2006 population pyramid. Data recorded on size. The_ variance is calculated as: 3) m(v_)=C R(v_,v_)- K incident cases of cancer were obtained from ministry Yi=1hiC R(vi,v__)-+(va) of health and medical education (in the non-infectious Where C R(v_,v_) is the with-area covariance. The diseases management center) of Iran. The major sources Area-to-Area Poisson kriging technique accomplished of data collection related to cancer were reports from using the public-domain executable poisson-kriging.exe pathology laboratories, hospitals and radiology clinics. described in Goovaerts (2005) The geographical units are 336 counties of display a wide range of size and shapes, which should favour Results Area-to-Area Poisson Kriging that implicitly accounts for the spatial support of the data in the analysis. The According to Figure1, crude rate and population at risk population-weighted average of cancer rate is 2.92 per mapped in top graph, risk estimated using Area-to-Area 100,000 person- years. Poisson kriging approach and corresponding prediction variance mapped in bottom graph. Crude rate mean is 2.70 Materials and Methods and estimated risk mean is 2.84 and prediction variance mean is 0.42. North, north west and north east counties The Area-to-Area Poisson kriging technique for have higher risk than other counties. the estimation of risk values is described in detailed in Goovaerts (2006). This section provides a brief recall of Discussion the approach.

Let v_ represent area supports and z(v_)=d(v_)/n(v_) Ignoring spatial support in parameter estimation may denote the observed incidence rates where d(v_) is the lead to more smoothing and less precise estimates. The number of recorded incidence case and n(v_) is the size objective of this paper was to illustrate esophagus cancer of population at risk. Area-to-Area Poisson kriging spatial incidence rate mapping by a geostatistic technique for interpolation is predict any area value z(v) using K area health data to the popular Area-to-Area Poisson kriging. K data neighboring units vi: 1) z(v_)= Yi=1hi(v_)z(v_) This approach account spatial support so generate less

Where hi(V_) are weights assigned to rates are smoothing and more precise than other approaches such K computed_ by solving the following equations:_ 2) Yj=1hj(v_) as BYM model and point Poisson kriging that ignore

{C R(vi,vj)+bij[m*/n(vi)]}++(va)=C R(vi,v_) i=1,...,K spatial support. K Yj=1hj(v_)=1. The Area-to-Area Poisson kriging approach is Where +(va) is the Lagrange parameter, bij=1 if i=j recommended for estimation of disease mapping and_ 0 otherwise. m* is the population-weighted mean, parameters, since this method accounts spatial support and C R(vi,vj) is the among-areas covariance and, n(vi) is the pattern in irregular spatial area. The results demonstrate size of the population at risk in area vi. The term m*/n(vi) that the counties in provinces Ardebil, Mazandaran and accounts for the variability resulting from the population Gilan have higher risk than other counties.

Figure 1. Esophagus Cancer Incidence Rate Per 100,000 Person Years During the Period 2003-2007 in Iran. Crude rates (top, left), Population at risk (top, right), risk estimated (by ATA Poisson kriging) (bottom, left), prediction variance (by ATA poisson kriging) (bottom, right) 12 $VLDQ3DFLÀF-RXUQDORI&DQFHU3UHYHQWLRQ9RO DOI:http://dx.doi.org/10.7314/APJCP.2013.14.1.11 Area-to-Area Poisson Kriging Analysis of County-Level Esophageal Cancer Incidence Rates in Iran In short, the risk of people developing esophagus cancer in Iran is heterogeneous during the period 2003- 2007. People living north of Iran had a higher chance of cancer risk than people living in other areas. Epidemiologists and investigators believe that the cause of high incidence in north is nitrate including soil and particular nourishing in those areas.

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