Displaying all 15 publications

  1. Faroughi, P., Ismail, N.
    This paper introduces new forms of bivariate generalized Poisson (BGP) and bivariate negative binomial (BNB) regression models which can be fitted to bivariate and correlated count data with covariates. The BGP and BNB regression models can be fitted to bivariate count data with positive, zero or negative correlations. Applications of new BGP and BNB regression models are illustrated on Australian health survey data.
    Matched MeSH terms: Poisson Distribution
  2. Goh J, Hj M Ali N
    PLoS ONE, 2015;10(7):e0132782.
    PMID: 26182211 DOI: 10.1371/journal.pone.0132782
    Over the last few decades, cubic splines have been widely used to approximate differential equations due to their ability to produce highly accurate solutions. In this paper, the numerical solution of a two-dimensional elliptic partial differential equation is treated by a specific cubic spline approximation in the x-direction and finite difference in the y-direction. A four point explicit group (EG) iterative scheme with an acceleration tool is then applied to the obtained system. The formulation and implementation of the method for solving physical problems are presented in detail. The complexity of computational is also discussed and the comparative results are tabulated to illustrate the efficiency of the proposed method.
    Matched MeSH terms: Poisson Distribution
  3. Nuzlinda Abdul Rahman, Abdul Aziz Jemain
    Sains Malaysiana, 2013;42:1003-1010.
    Infant mortality is one of the central public issues in most of the developing countries. In Malaysia, the infant mortality rates have improved at the national level over the last few decades. However, the issue concerned is whether the improvement is uniformly distributed throughout the country. The aim of this study was to investigate the geographical distribution of infant mortality in Peninsular Malaysia from the year 1970 to 2000 using a technique known as disease mapping. It is assumed that the random variable of infant mortality cases comes from Poisson distribution. Mixture models were used to find the number of optimum components/groups for infant mortality data for every district in Peninsular Malaysia. Every component is assumed to have the same distribution, but different parameters. The number of optimum components were obtained by maximum likelihood approach via the EM algorithm. Bayes theorem was used to determine the probability of belonging to each district in every components of the mixture distribution. Each district was assigned to the component that had the highest posterior probability of belonging. The results obtained were visually presented in maps. The analysis showed that in the early year of 1970, the spatial heterogeneity effect was more prominent; however, towards the end of 1990, this pattern tended to disappear. The reduction in the spatial heterogeneity effect in infant mortality data indicated that the provisions of health services throughout the Peninsular Malaysia have improved over the period of the study, particularly towards the year 2000.
    Matched MeSH terms: Poisson Distribution
  4. Cheong YL, Burkart K, Leitão PJ, Lakes T
    Int J Environ Res Public Health, 2013 Dec;10(12):6319-34.
    PMID: 24287855 DOI: 10.3390/ijerph10126319
    The number of dengue cases has been increasing on a global level in recent years, and particularly so in Malaysia, yet little is known about the effects of weather for identifying the short-term risk of dengue for the population. The aim of this paper is to estimate the weather effects on dengue disease accounting for non-linear temporal effects in Selangor, Kuala Lumpur and Putrajaya, Malaysia, from 2008 to 2010. We selected the weather parameters with a Poisson generalized additive model, and then assessed the effects of minimum temperature, bi-weekly accumulated rainfall and wind speed on dengue cases using a distributed non-linear lag model while adjusting for trend, day-of-week and week of the year. We found that the relative risk of dengue cases is positively associated with increased minimum temperature at a cumulative percentage change of 11.92% (95% CI: 4.41-32.19), from 25.4 °C to 26.5 °C, with the highest effect delayed by 51 days. Increasing bi-weekly accumulated rainfall had a positively strong effect on dengue cases at a cumulative percentage change of 21.45% (95% CI: 8.96, 51.37), from 215 mm to 302 mm, with the highest effect delayed by 26-28 days. The wind speed is negatively associated with dengue cases. The estimated lagged effects can be adapted in the dengue early warning system to assist in vector control and prevention plan.
    Matched MeSH terms: Poisson Distribution
  5. Hosseinpour M, Sahebi S, Zamzuri ZH, Yahaya AS, Ismail N
    Accid Anal Prev, 2018 Sep;118:277-288.
    PMID: 29861069 DOI: 10.1016/j.aap.2018.05.003
    According to crash configuration and pre-crash conditions, traffic crashes are classified into different collision types. Based on the literature, multi-vehicle crashes, such as head-on, rear-end, and angle crashes, are more frequent than single-vehicle crashes, and most often result in serious consequences. From a methodological point of view, the majority of prior studies focused on multivehicle collisions have employed univariate count models to estimate crash counts separately by collision type. However, univariate models fail to account for correlations which may exist between different collision types. Among others, multivariate Poisson lognormal (MVPLN) model with spatial correlation is a promising multivariate specification because it not only allows for unobserved heterogeneity (extra-Poisson variation) and dependencies between collision types, but also spatial correlation between adjacent sites. However, the MVPLN spatial model has rarely been applied in previous research for simultaneously modelling crash counts by collision type. Therefore, this study aims at utilizing a MVPLN spatial model to estimate crash counts for four different multi-vehicle collision types, including head-on, rear-end, angle, and sideswipe collisions. To investigate the performance of the MVPLN spatial model, a two-stage model and a univariate Poisson lognormal model (UNPLN) spatial model were also developed in this study. Detailed information on roadway characteristics, traffic volume, and crash history were collected on 407 homogeneous segments from Malaysian federal roads. The results indicate that the MVPLN spatial model outperforms the other comparing models in terms of goodness-of-fit measures. The results also show that the inclusion of spatial heterogeneity in the multivariate model significantly improves the model fit, as indicated by the Deviance Information Criterion (DIC). The correlation between crash types is high and positive, implying that the occurrence of a specific collision type is highly associated with the occurrence of other crash types on the same road segment. These results support the utilization of the MVPLN spatial model when predicting crash counts by collision manner. In terms of contributing factors, the results show that distinct crash types are attributed to different subsets of explanatory variables.
    Matched MeSH terms: Poisson Distribution
  6. Simoneau G, Levis B, Cuijpers P, Ioannidis JPA, Patten SB, Shrier I, et al.
    Biom J, 2017 Nov;59(6):1317-1338.
    PMID: 28692782 DOI: 10.1002/bimj.201600184
    Individual patient data (IPD) meta-analyses are increasingly common in the literature. In the context of estimating the diagnostic accuracy of ordinal or semi-continuous scale tests, sensitivity and specificity are often reported for a given threshold or a small set of thresholds, and a meta-analysis is conducted via a bivariate approach to account for their correlation. When IPD are available, sensitivity and specificity can be pooled for every possible threshold. Our objective was to compare the bivariate approach, which can be applied separately at every threshold, to two multivariate methods: the ordinal multivariate random-effects model and the Poisson correlated gamma-frailty model. Our comparison was empirical, using IPD from 13 studies that evaluated the diagnostic accuracy of the 9-item Patient Health Questionnaire depression screening tool, and included simulations. The empirical comparison showed that the implementation of the two multivariate methods is more laborious in terms of computational time and sensitivity to user-supplied values compared to the bivariate approach. Simulations showed that ignoring the within-study correlation of sensitivity and specificity across thresholds did not worsen inferences with the bivariate approach compared to the Poisson model. The ordinal approach was not suitable for simulations because the model was highly sensitive to user-supplied starting values. We tentatively recommend the bivariate approach rather than more complex multivariate methods for IPD diagnostic accuracy meta-analyses of ordinal scale tests, although the limited type of diagnostic data considered in the simulation study restricts the generalization of our findings.
    Matched MeSH terms: Poisson Distribution
  7. Hosseinpour M, Yahaya AS, Sadullah AF
    Accid Anal Prev, 2014 Jan;62:209-22.
    PMID: 24172088 DOI: 10.1016/j.aap.2013.10.001
    Head-on crashes are among the most severe collision types and of great concern to road safety authorities. Therefore, it justifies more efforts to reduce both the frequency and severity of this collision type. To this end, it is necessary to first identify factors associating with the crash occurrence. This can be done by developing crash prediction models that relate crash outcomes to a set of contributing factors. This study intends to identify the factors affecting both the frequency and severity of head-on crashes that occurred on 448 segments of five federal roads in Malaysia. Data on road characteristics and crash history were collected on the study segments during a 4-year period between 2007 and 2010. The frequency of head-on crashes were fitted by developing and comparing seven count-data models including Poisson, standard negative binomial (NB), random-effect negative binomial, hurdle Poisson, hurdle negative binomial, zero-inflated Poisson, and zero-inflated negative binomial models. To model crash severity, a random-effect generalized ordered probit model (REGOPM) was used given a head-on crash had occurred. With respect to the crash frequency, the random-effect negative binomial (RENB) model was found to outperform the other models according to goodness of fit measures. Based on the results of the model, the variables horizontal curvature, terrain type, heavy-vehicle traffic, and access points were found to be positively related to the frequency of head-on crashes, while posted speed limit and shoulder width decreased the crash frequency. With regard to the crash severity, the results of REGOPM showed that horizontal curvature, paved shoulder width, terrain type, and side friction were associated with more severe crashes, whereas land use, access points, and presence of median reduced the probability of severe crashes. Based on the results of this study, some potential countermeasures were proposed to minimize the risk of head-on crashes.
    Matched MeSH terms: Poisson Distribution
  8. Hosseinpour M, Pour MH, Prasetijo J, Yahaya AS, Ghadiri SM
    Traffic Inj Prev, 2013;14(6):630-8.
    PMID: 23859313 DOI: 10.1080/15389588.2012.736649
    The objective of this study was to examine the effects of various roadway characteristics on the incidence of pedestrian-vehicle crashes by developing a set of crash prediction models on 543 km of Malaysia federal roads over a 4-year time span between 2007 and 2010.
    Matched MeSH terms: Poisson Distribution
  9. Yen FY, Chong KM, Ha LM
    PLoS ONE, 2013;8(6):e65440.
    PMID: 23755231 DOI: 10.1371/journal.pone.0065440
    This paper proposes three synthetic-type control charts to monitor the mean time-between-events of a homogenous Poisson process. The first proposed chart combines an Erlang (cumulative time between events, Tr ) chart and a conforming run length (CRL) chart, denoted as Synth-Tr chart. The second proposed chart combines an exponential (or T) chart and a group conforming run length (GCRL) chart, denoted as GR-T chart. The third proposed chart combines an Erlang chart and a GCRL chart, denoted as GR-Tr chart. By using a Markov chain approach, the zero- and steady-state average number of observations to signal (ANOS) of the proposed charts are obtained, in order to evaluate the performance of the three charts. The optimal design of the proposed charts is shown in this paper. The proposed charts are superior to the existing T chart, Tr chart, and Synth-T chart. As compared to the EWMA-T chart, the GR-T chart performs better in detecting large shifts, in terms of the zero- and steady-state performances. The zero-state Synth-T4 and GR-Tr (r = 3 or 4) charts outperform the EWMA-T chart for all shifts, whereas the Synth-Tr (r = 2 or 3) and GR-T 2 charts perform better for moderate to large shifts. For the steady-state process, the Synth-Tr and GR-Tr charts are more efficient than the EWMA-T chart in detecting small to moderate shifts.
    Matched MeSH terms: Poisson Distribution
  10. Seow A, Duffy SW, McGee MA, Lee J, Lee HP
    Int J Epidemiol, 1996 Feb;25(1):40-5.
    PMID: 8666502
    BACKGROUND: Breast cancer is the most commonly occurring cancer among women in Singapore, a country which has experienced significant changes in lifestyle over the past three decades. The increase in incidence of the disease is a matter of some concern.

    METHODS: Data from the population-based Singapore Cancer Registry for 1968-1992 were used to determine time trends, inter-ethnic differences and the contributions of age, period and cohort effects to the incidence of the disease.

    RESULTS: Our results revealed an average annual increase of 3.6% over the 25-year period for all women, form 20.2 per 100,000 women in the period 1968-1972 to 38.8 per 100,000 in 1988-1992. There was a statistically significant difference between the three major ethnic groups, the rate of increase being highest in Malays (4.4%) and lowest in Indians (1.4%). The overall increase was attributable to a strong cohort effect that remained significant when adjusted for time period for Chinese women and for all ethnic groups combined. The risk was observed to increase in successive birth cohorts from the 1890s to 1960s.

    CONCLUSIONS: Our results suggest that breast cancer incidence rates are likely to continue to increase more sharply in the future as women born after the mid-20th century reach the high-risk age groups. They also suggest the pattern by which important aetiological factors for the disease in our population have exerted their effects, and provide support for the role of demographic and lifestyle changes as possible risk factors.

    Matched MeSH terms: Poisson Distribution
  11. Seow A, Lee J, Sng I, Fong CM, Lee HP
    Cancer, 1996 May 1;77(9):1899-904.
    PMID: 8646691
    BACKGROUND: Non-Hodgkin's lymphoma has increased in incidence in many countries, particularly in the West. Advances in diagnostic methods and the understanding of the disease over time pose a challenge to the interpretation of these trends. The aim of this study was to determine if the disease has increased in Singapore, a newly industrialized Asian country, and to examine the possible factors that may account for any observed changes.
    METHODS: Data from the population-based Singapore Cancer Registry for the period 1968 to 1992 were reviewed to determine time trends based on sex and ethnic group. The Poisson regression model was fitted to the cross-tabulated data to obtain the adjusted incidence density ratios.
    RESULTS: A total of 1988 cases of non-Hodgkin's lymphoma were included in the analysis. There was an overall increase in incidence among both Chinese and Malaysians. However, the rate of increase was greater in females (age-standardized rate from 1.8 per 100,000 in 1968-1972 to 4.5 per 100,000 in 1988-1992) than in males (3.2 per 100,000 to 5.9 per 100,000 in the same time periods). Between ethnic groups, Malay females were at higher overall risk compared with their Chinese counterparts (incidence density ratio 1.32; 95% confidence interval, 1.08-1.61). Although a substantial proportion of patients diagnosed with Hodgkin's disease between 1968 and 1972 were reclassified on review, using present criteria, as having non-Hodgkin's lymphoma, it is unlikely that this, and other recent changes in histologic interpretation, could have accounted for an increase of this magnitude.
    CONCLUSIONS: Non-Hodgkin's lymphoma has increased in incidence among the Chinese and Malay populations in Singapore. The pattern of increase differs from that of the common cancer sites, and suggests the need to look for environmental and genetic factors that have not yet been elucidated.
    Matched MeSH terms: Poisson Distribution
  12. Chew CH, Woon YL, Amin F, Adnan TH, Abdul Wahab AH, Ahmad ZE, et al.
    BMC Public Health, 2016 08 18;16(1):824.
    PMID: 27538986 DOI: 10.1186/s12889-016-3496-9
    BACKGROUND: Each year an estimated 390 million dengue infections occur worldwide. In Malaysia, dengue is a growing public health concern but estimate of its disease burden remains uncertain. We compared the urban-rural difference of dengue seroprevalence and determined age-specific dengue seroprevalence in Malaysia.

    METHODS: We undertook analysis on 11,821 subjects from six seroprevalence surveys conducted in Malaysia between 2001 and 2013, which composed of five urban and two rural series.

    RESULTS: Prevalence of dengue increased with age in both urban and rural locations in Malaysia, which exceeded 90 % among those aged 70 years or beyond. The age-specific rates of the 5 urban surveys overlapped without clear separation among them, while prevalence was lower in younger subjects in rural series than in urban series, the trend reversed in older subjects. There were no differences in the seroprevalence by gender, ethnicity or region. Poisson regression model confirmed the prevalence have not changed in urban areas since 2001 but in rural areas, there was a significant positive time trend such that by year 2008, rural prevalence was as high as in urban areas.

    CONCLUSION: Dengue seroprevalence has stabilized but persisted at a high level in urban areas since 2001, and is fast stabilizing in rural areas at the same high urban levels by 2008. The cumulative seroprevalence of dengue exceeds 90 % by the age of 70 years, which translates into 16.5 million people or 55 % of the total population in Malaysia, being infected by dengue by 2013.

    Matched MeSH terms: Poisson Distribution
  13. Zamri EN, Moy FM, Hoe VC
    PLoS ONE, 2017;12(2):e0172195.
    PMID: 28234933 DOI: 10.1371/journal.pone.0172195
    BACKGROUND: Musculoskeletal pain is common among teachers. Work-related psychosocial factors are found to be associated with the development of musculoskeletal pain, however psychological distress may also play an important role.

    OBJECTIVES: To assess the prevalence of self-reported low back pain (LBP), and neck and/or shoulder pain (NSP) among secondary school teachers; and to evaluate the association of LBP and NSP with psychological distress and work-related psychosocial factors.

    METHODS: This was a cross-sectional study conducted among teachers in the state of Penang, Malaysia. The participants were recruited via a two stage sampling method. Information on demographic, psychological distress, work-related psychosocial factors, and musculoskeletal pain (LBP and NSP) in the past 12 months was collected using a self-administered questionnaire. Poisson regression was used to estimate the prevalence ratio (PR) for the associations between psychological distress and work-related psychosocial factors with LBP and NSP.

    RESULTS: The prevalence of self-reported LBP and NSP among 1482 teachers in the past 12 months was 48.0% (95% Confidence Interval (CI) 45.2%, 50.9%) and 60.1% (95% CI 57.4%, 62.9%) respectively. From the multivariate analysis, self-reported LBP was associated with teachers who reported severe to extremely severe depression (PR: 1.71, 95% CI 1.25, 2.32), severe to extremely severe anxiety (1.46, 95% CI 1.22, 1.75), high psychological job demand (1.29, 95% CI 1.06, 1.57), low skill discretion (1.28, 95% CI 1.13, 1.47) and poorer mental health (0.98, 95% CI 0.97, 0.99). Self-reported NSP was associated with mild to moderate anxiety (1.18, 95% CI 1.06, 1.33), severe to extremely severe anxiety (1.25, 95% CI 1.09, 1.43), low supervisory support (1.13, 95% CI 1.03, 1.25) and poorer mental health (0.98, 95% CI 0.97, 0.99).

    CONCLUSIONS: Self-reported LBP and NSP were common among secondary school teachers. Interventions targeting psychological distress and work-related psychosocial characteristics may reduce musculoskeletal pain among school teachers.

    Matched MeSH terms: Poisson Distribution
  14. Wong YL, Chinna K, Mariapun J, Wong LP, Khoo EM, Low WY, et al.
    Prev Med, 2013;57 Suppl:S24-6.
    PMID: 23318158 DOI: 10.1016/j.ypmed.2013.01.004
    OBJECTIVES: To identify the correlates between risk perceptions and cervical cancer screening among urban Malaysian women.
    METHOD: A cross-sectional household survey was conducted among 231 women in Petaling Jaya city in 2007. The association of risk perceptions of cervical cancer and screening practice was analyzed using Poisson regression.
    RESULTS: 56% of the respondents ever had a Pap smear test. Knowledge of signs and symptoms (aPR=1.11, 95% CI=1.03-1.19), age (aPR=1.02, 95% CI=1.01-1.03), number of pregnancies (aPR=1.06, 95% CI=1.01-1.11), marital status, education level and religion were found to be significant correlates of Pap smear screening. Respondents who were never married were less likely to have had a Pap smear. Those who had no education or primary education were less likely to have had a Pap smear compared to those with degree qualification. The prevalence of screening was significantly higher among Christians and others (aPR=1.35; 95% CI=1.01-1.81) and Buddhists (aPR=1.38; 95% CI=1.03-1.84), compared to Muslims.
    CONCLUSION: Eliminating anecdotal beliefs as risks via targeted knowledge on established risk factors and culturally sensitive screening processes are strategic for increasing and sustaining uptake of Pap smear screening versus current opportunistic screening practices.
    KEYWORDS: Cervical cancer; Malaysia; Pap smear; Risk perception; Screening; Targeted knowledge
    Matched MeSH terms: Poisson Distribution
  15. Tanuma J, Jiamsakul A, Makane A, Avihingsanon A, Ng OT, Kiertiburanakul S, et al.
    PLoS ONE, 2016;11(8):e0161562.
    PMID: 27560968 DOI: 10.1371/journal.pone.0161562
    BACKGROUND: In resource-limited settings, routine monitoring of renal function during antiretroviral therapy (ART) has not been recommended. However, concerns for tenofovir disoproxil fumarate (TDF)-related nephrotoxicity persist with increased use.

    METHODS: We investigated serum creatinine (S-Cr) monitoring rates before and during ART and the incidence and prevalence of renal dysfunction after starting TDF by using data from a regional cohort of HIV-infected individuals in the Asia-Pacific. Time to renal dysfunction was defined as time from TDF initiation to the decline in estimated glomerular filtration rate (eGFR) to <60 ml/min/1.73m2 with >30% reduction from baseline using the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation or the decision to stop TDF for reported TDF-nephrotoxicity. Predictors of S-Cr monitoring rates were assessed by Poisson regression and risk factors for developing renal dysfunction were assessed by Cox regression.

    RESULTS: Among 2,425 patients who received TDF, S-Cr monitoring rates increased from 1.01 to 1.84 per person per year after starting TDF (incidence rate ratio 1.68, 95%CI 1.62-1.74, p <0.001). Renal dysfunction on TDF occurred in 103 patients over 5,368 person-years of TDF use (4.2%; incidence 1.75 per 100 person-years). Risk factors for developing renal dysfunction included older age (>50 vs. ≤30, hazard ratio [HR] 5.39, 95%CI 2.52-11.50, p <0.001; and using PI-based regimen (HR 1.93, 95%CI 1.22-3.07, p = 0.005). Having an eGFR prior to TDF (pre-TDF eGFR) of ≥60 ml/min/1.73m2 showed a protective effect (HR 0.38, 95%CI, 0.17-0.85, p = 0.018).

    CONCLUSIONS: Renal dysfunction on commencing TDF use was not common, however, older age, lower baseline eGFR and PI-based ART were associated with higher risk of renal dysfunction during TDF use in adult HIV-infected individuals in the Asia-Pacific region.

    Matched MeSH terms: Poisson Distribution
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