Sains Malaysiana 45(11)(2016): 1741–1745

 

New Approach to Calculate the Denominator for the Relative Risk Equation

(Pendekatan Baharu untuk Menghitung Pembawah bagi Persamaan Risiko Relatif)

 

NOR AZAH SAMAT* & SYAFIQAH HUSNA MOHD IMAM MA’AROF

 

Department of Mathematics, Faculty of Science and Mathematics, Universiti Pendidikan Sultan Idris, 35900 Tanjong Malim, Perak Darul Ridzuan, Malaysia

 

Received: 21 May 2015/Accepted: 24 March 2016

 

ABSTRACT

Disease frequency is used to measure the situation of the disease with reference to the population size and time period which is in a fractional form. The lower part of the fraction, known as denominator is the important part as it was used to calculate a rate or ratio. Since the disease frequency is based on a ratio estimator, the results are highly dependent upon the value of denominator. Therefore, the main aim of this paper was to propose a new method in calculating the denominator for the relative risk equation with the application to chikungunya disease data from Malaysia. The new method of calculating the denominator of the relative risk equation includes the use of discrete time-space stochastic SIR-SI (susceptible-infective-recovered for human population and susceptible-infective for vector population) disease transmission model instead of the total disease counts. The results of the analysis showed that the estimation of expected disease counts based on total posterior means can overcome the problem of expected counts estimation based on the total number of disease especially when there is no observed disease count in certain regions. The proposed new approach to calculate the denominator for the relative risk equation is suitable for the case of rare disease in which it offers a better method of expected disease counts estimation.

 

Keywords: Chikungunya disease; disease mapping; relative risk estimation; SIR-SI disease transmission model

 

ABSTRAK

Frekuensi penyakit digunakan untuk mengukur situasi sesuatu penyakit dengan merujuk kepada saiz populasi dan tempoh masa yang berbentuk pecahan. Bahagian bawah pecahan, yang dikenali sebagai pembawah ialah bahagian yang penting kerana ia digunakan untuk menghitung suatu kadar atau nisbah. Memandangkan frekuensi penyakit adalah berasaskan suatu anggaran nisbah, keputusan anggaran sangat bergantung kepada nilai pembawah tersebut. Oleh itu, matlamat utama kajian ini ialah untuk mencadangkan suatu kaedah baharu dalam mengira pembawah bagi persamaan risiko relatif dengan aplikasi kepada data penyakit chikungunya dari Malaysia. Kaedah baru pengiraan pembawah bagi persamaan risiko relatif mengambil kira penggunaan model jangkitan penyakit stokastik diskrit masa-ruang SIR-SI (rentan-jangkitan-pulih bagi populasi manusia, rentan-jangkitan bagi populasi vektor) dan bukan jumlah bilangan penyakit. Hasil analisis menunjukkan bahawa penganggaran bilangan jangkaan penyakit berdasarkan jumlah posterior min dapat mengatasi masalah penganggaran jumlah jangkaan berdasarkan jumlah bilangan penyakit khususnya apabila tiada penyakit yang diperhatikan dalam sesuatu kawasan. Kaedah baru yang dicadangkan untuk mengira pembawah bagi persamaan risiko relatif adalah sesuai bagi kes penyakit yang jarang berlaku kerana ia menawarkan kaedah yang lebih baik bagi penganggaran bilangan jangkaan penyakit.

 

Kata kunci: Model jangkitan penyakit SIR-SI; pemetaan penyakit; penganggaran risiko relatif; penyakit chikungunya

 

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*Corresponding author; email: norazah@fsmt.upsi.edu.my