Browsing by Author "Attanayake, A.M.C.H."

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COMPARISON OF PERFORMANCES OFSELECTED FORECASTING MODELS:AN APPLICATION TO DENGUE DATA IN COLOMBO, SRI LANKA
(Department of Statistics & Computer Science, Faculty of Science,& Research & Development Centre for Mathematical Modelling, Faculty of Science, University of Colombo, Sri Lanka., 2021) Attanayake, A.M.C.H.; Perera, S.S.N.; Liyanage, U.P.
Dengue is a one of the diseases in the world which has no exact treatment to recover from the disease. It is rapidly spreading throughout the world by causing large number of deaths [1]. In Sri Lanka, there is an increase of reported dengue cases over recent years. The majority of dengue cases reported in the Colombo district within the Sri Lanka. Effective dengue management and controlling strategies should be implemented to reduce the deaths from the disease. Modelling and predicting the distribution of the dengue will be useful in detecting outbreaks of the dengue and to execute controlling actions beforehand. The objective of this study is to develop an appropriate modelling technique to predict dengue cases. To accomplish this objective, we have chosen our study area as Colombo, Sri Lanka. Seven modelling techniques, namely, Na¨ıve, Seasonal Na¨ıve, Random Walk with Drift, Mean Forecasting, Autoregressive Integrated Moving Average, Exponential Smoothing and TBATS (Trigonometric, Box-Cox Transformation, ARMA errors, Trend and Seasonal components) [2] were chosen in this study to model dengue data. For model development process, monthly reported dengue cases in Colombo from January 2010 to December 2018 were used and validated using the data from January to December in 2019. Mean error, root mean squared error and mean absolute percentage error measurements were used to select the most parsimonious model to predict dengue cases in Colombo, Sri Lanka. Both Exponential and TBATS models were competed in predicting dengue cases by reporting minimum error measures. Therefore, results disclosed that among the selected methods either Exponential Smoothing model or TBATS model can be used to predict dengue cases in Colombo, Sri Lanka.
Development of a Minitab Macro Program as a Remedy to Overcome Heteroscedasticity in Linear Regressions
(University of Kelaniya, 2008) Attanayake, A.M.C.H.; Hewapathirana, T.K.
Homoscedasticity in the disturbance terms that appear in a regression function is one of the key assumptions of ordinary least squares analysis. As the developed regression model relies heavily on the model assumptions, violation of the assumptions severely affects the importance of a regression model. Transforming the response variable is one solution to overcome the problem of heteroscedasticity. Today most statistical packages use graphical methods to detect heteroscedasticity. Although a graphical method could be considered as a good starting point, no measure of reliability can be attached to inferences derived from a graphical method. In this study we have developed a Minitab macro to detect heteroscedasticity present in the disturbance terms by the use of graphical as well as statistical methods including the popular White's General Heteroscedasticity test and how to solve the heteroscedasticity problem by applying the alternative form of the Box-Cox power transformation. The alternative form of the Box-Cox transformation is given by: V= Yln(Y) A=O Where lnY= n-'I lnY; Considering the stability of V for minor changes in the power parameter A, the transformed variable, V is chosen for the analysis and useful values of A were found to be in the range [-2, 2]. The program was developed using a Local macro structure and tested on Minitab version 14 and requires Microsoft Windows 2000 or XP operating system to implement this program. The developed macro was tested for many data sets and was found that the program is capable in handling the heteroscedasticity present in the error structure.
A Fuzzy Linear Model Using Possibilistic Linear Regression with Least Squares Method: An Application to Dengue and Rainfall Data
(International Postgraduate Research Conference 2019, Faculty of Graduate Studies, University of Kelaniya, Sri Lanka, 2019) Attanayake, A.M.C.H.; Perera, S.S.N.; Liyanage, U.P.
Fuzzy linear models deal with vague and imprecise phenomenon in order to represent better models. These type of models are especially suitable in modelling and predicting dengue disease as the disease associated with various unknown and uncontrollable factors. Further, modelling and predicting the dengue disease is important as it is one of the leading diseases in the world which reports higher number of deaths. This study focuses on modelling reported dengue cases in the Colombo district, Sri Lanka. Particularly, Possibilistic Linear Regression with Least Squares (PLRLS) Method was applied as the modelling procedure. This method was proposed by H. Lee and H. Tanaka in 1999 to deal with crisp inputs and fuzzy output. The rainfall as one of the leading climatic factors that associated with dengue disease included in the model as an independent variable. Data consists of weekly reported dengue cases and weekly average rainfall in the Colombo district from 46th week of 2009 to 12th week of 2015. 2009 to 2014 data were used for model development and rest of the data for model validation. Cross correlation analysis revealed that the rainfall with 10 lags was associated with the reported dengue cases. By considering dengue and rainfall data as crisp inputs, the upper approximation model and lower approximation model were obtained to reflect the fuzziness of the dengue count in the district. The developed coefficients of the fuzzy linear regression were in the form of non-symmetric triangular fuzzy numbers. The left and the right spreads of the central value determined the lower and upper boundary of the interval, respectively, where the corresponding degree of membership equals to 0. The predicted values from the fuzzy regression model and the actual values of the validation set were within the upper and lower approximation models which indicated the possibility of the dengue prediction through PLRLS method. The authors are in the process of testing additional fuzzy linear models by changing fuzzy input/output combinations with incorporating more independent variables.
Identifying Factors Associated with Price Categories of Motorcycles in Sri Lanka using Discriminant Analysis
(Department of Statistics & Computer Science, University of Kelaniya, Sri Lanka, 2021) Chanika, P.A.L.; Attanayake, A.M.C.H.; Gunaratne, M.D.N.
The motorcycle is one of the most popular modes of transportation in Asia because it is a fast, economic and convenient mode of transportation. According to the motor vehicle registration statistics of the department of motor traffic, motorcycle is the best-selling vehicle in Sri Lanka. Pricing of the motorcycles is one of the major concerns for motorcycle byers and importers. The purposes of this study are to identify the factors which are associated with the prices of motorcycles and to construct a model to determine the price of a motorcycle based on significant factors. Specifications and features of selected motorcycles were collected from secondary data sources. ‘Motorcycle Category’, ‘Fuel Efficiency’, ‘Engine Power’, ‘Brake System’, ‘Torque’, ‘Length’ were the significant factors which had an association between the price categories of motorcycles among 15 properties of motorcycles considered under study. The canonical discriminant analysis was used to develop the model and to predict the price categories of motorcycles. The significant categorical variables were used as the dummy variables. Torque was omitted from the model because of the presence of multicollinearity. The two significant discriminant functions were classified the data into four categories of price. The 75% responds were correctly classified into four price categories. Motorcycle category, Fuel Efficiency, Engine Power, Brake System and Length were found as significantly associated factors to the prices of motorcycles. Decision makers in the field can make good use of those factors in developing their pricing strategies in the motorcycle industry
MODELING COVID-19 CASES IN SRI LANKA USING ARIMA MODELS
(The Open University Of Srilanka., 2020) Attanayake, A.M.C.H.; Perera, S.S.N.
COVID-19 (Novel Coronavirus) is a pandemic which spread around the world at an alarming rate. As of 10th June 2020, 1,880 infections and 11 deaths were reported in Sri Lanka due to COVID-19. The number of infections increase day by day requiring research on modelling the pandemic. Modelling of COVID 19 cases will be useful to understand the behavioural patterns of the disease and hence to identify control mechanisms. The aim of this study is to model and predict the daily cumulative COVID-19 cases in Sri Lanka. Autoregressive Integrated Moving Average (ARIMA) technique was applied to model the reported COVID-19 cases in Sri Lanka. Data from 11th March - 1st of June 2020 were used for the model development and data from 2nd - 10th June 2020 (10% of data) were used for model validation. In the analysis, second order differencing removed the non-stationarity of the original series. Different candidate ARIMA models were tested based on ACF and PACF plots and the best ARIMA model was selected based on minimum AIC and BIC measures. The most appropriate ARIMA model for the COVID-19 cases in Sri Lanka is ARIMA (2,2,2). After verifying the assumptions of the model, MAPE of the validation set revealed 1.86%. Therefore, the selected most appropriate model was used to forecast the future COVID-19 cases in Sri Lanka. According to the forecasted values of the model, it can be concluded that COVID19 cases in Sri Lanka will increase slowly in the upcoming days. ARIMA technique is appropriate in only short-term forecasting. Availability of an effective prediction model will be helpful in anticipating the cases and to take timely action to control the COVID-19 incidence. Unexpected recordings cannot be modelled and predicted by the fitted models. Uncertainties limit the effectiveness of a model, specially, in an epidemic like novel coronavirus.
Study on monthly expenditures of undergraduates of Faculty of Science, University of Kelaniya
(Faculty of Science, University of Kelaniya, Sri Lanka, 2016) Gunawardana, K.M.A.R.S.; Madhubashini, M.G.A.K.; Madhumali, N.G.M.; Nanayakkara, K.A.D.C.N.; Nuwanthika, G.G.T.; Pandgamage, I.D.; Rangari, S.C.; Samanpitiya, H.M.I.; Sandamali, H.D.S.; Sandhamali, N.P.A.A.; Pitigalaarachchi, P.A.A.C.; Attanayake, A.M.C.H.
There are lots of changes in students’ lives after transition from school to university. Students face new challenges and expenditures of students are varied with these changes. The aim of this study is to understand the monthly expenditures of 1st, 2nd and 3rd year undergraduates of faculty of science, University of Kelaniya. The objectives of this study are to estimate the average monthly expenditure of a student of the Faculty of Science, classify the average monthly expenditure with respect to gender and year of study, estimate the average monthly expenditure on food, travelling, residence, mobile phones and internet usage, understand the ways that the students cover their expenditures and estimate their satisfaction level on income and expenditure. The data required for this study was gathered through a survey which was conducted during the period of September – November 2015. Among the 1394 students registered in the faculty of science 159 respondents were randomly selected using stratified random sampling method (without replacement). 37% of the students’ average monthly expenditure is in the range of Rs.5000-Rs.8000. Further the majority of the male students (35%) and majority of the female students (40%) average monthly expenditure is in the same range. This range is not differently recorded for 1st, 2nd and 3rd year students’ maximum average monthly expenditure ranges as well. The second majority (24%) of the students average monthly expenditure range is Rs.8000-Rs.10000. Fifty three percent of the students’ average monthly expenditure for food is above Rs.2000. The maximum percentage (31%) of students’ average monthly expenditure for travelling and residence is in the range of Rs.1000–Rs.2000. The expenditure for mobile phones and internet usage is Rs.500– Rs.1000. More than 75% of students receive money from their parents to cover their monthly expenditures. Less than 50% of the students engage in part time jobs to cover their expenditures. Forty six percent of students receive between Rs.3000- Rs.6000 every month from their part time jobs. The highest percentage (73%) of them are engaged in tuition as their part time job. Nearly 52% of the students of the Faculty of Science receive scholarships; Mahapola or Bursary. Students cover their expenditures by doing part time jobs and they receive money from the parents and scholarships. Approximately 33% of the undergraduates moderately satisfied about their income and expenditure. The results of this survey will be useful for students to understand and manage their expenditures in a proper way.
A survey on usage of canteens of University of Kelaniya by students of Faculty of Science
(Faculty of Science, University of Kelaniya, Sri Lanka, 2016) Dias, S.N.U.P.; Priyasad, H.A.D.; Manamperi, D.K.S.; Kumara, M.S.M.S.; Sandaruwan, D.M.S.; Pramoda, K. A.D.A.; Fernando, T.S.D.; Rashmi, W.A.D.; Ravindran, U.M.; Dhananjani, W.T.; Pitigalaarachchi, P.A.A.C.; Attanayake, A.M.C.H.
The university canteens while providing meals are an important meeting point for both students and staff members. There are several canteens within a university but service provided by canteens and therefore, students’ preferences for canteens may be different. This survey is based on five main canteens at the University of Kelaniya; Base, Gym, Hilton, Staff and Hostel canteens. The aim of this survey is to understand the usage of the canteens by students of the Faculty of Science. The objectives are to identify the frequently visited canteen of the students and the reasons for it, categorize the most visited canteen by gender, year of study, accommodation type, measure the satisfaction on available facilities of university canteens and classify the student expectations regarding the facilities. The survey was conducted during the period of September – November 2015. Among the 1394 students registered in the Faculty of Science, 255 respondents were randomly selected using simple random sampling method (without replacement). An appropriate questionnaire was developed in order to gather data and achieve the objectives. After a pilot survey was conducted, questionnaire was administered in person and online and also by interviewing busy students in order to collect data. The analysis reveals that the majority of students (41%) of the Faculty of Science visited Base canteen for their needs; whereas 25% visited Staff canteen and 22% visit the Gym canteen. The usage does not change irrespective of whether the student stays at the hostel, boarding place or home. The reason for using the Base canteen is convenience in reaching the canteen. Female students (49%) use the Base canteen whereas male students (38%) prefer to use Staff canteen. Lunch is the preferred meal compared to breakfast, dinner and other snacks. The majority of first year students visit the Base canteen, 2nd year students prefer to visit Gym and Staff canteens than the Base canteen and 3rd year students prefer the Base canteen. Majority of the students (29%) have ranked the condition of Base canteen as average and 14% have ranked as good. When considering the attitude of the staff members of the canteens, Base and Staff canteens’ employees have been highly ranked as ‘Average’ by most of the respondents (19% and 17% respectively) while ‘Good’ was marked by 15%. Most of the respondents have marked as ‘Average’ considering the service speed of canteens in the university and around 20% of students have claimed that the service speed is low over all canteens. In general, only 45% of the students are satisfied with the facilities provided by the canteens. Most of the students (23%) have requested to expand the space within the canteens and requested to have air conditioning, TVs and vending machines within the canteens. The survey discloses important findings about the usage of university canteens by students of the Faculty of Science.
Survey on usage of university main library by undergraduates of Faculty of Science, University of Kelaniya.
(International Research Symposium on Pure and Applied Sciences, 2017 Faculty of Science, University of Kelaniya, Sri Lanka., 2017) Sandamali, L. B. U.; Dhananjani, G. L. I.; Manchanayake, M. A. S. N.; Perera, M. S. H.; Madhushika, P. A. L.; Jayasanka, P. G. Y.; Edirisinghe, E. C. D.; Premathilaka, R. A. N. M.; Rajapaksha, M. O. S.; Senewirathne, A. P. D. S.; Attanayake, A.M.C.H.
The main library of the University of Kelaniya plays a major role in advancing knowledge of its users. It provides a huge collection of reading materials for reference use or lending. The aim of this study is to understand the usage of main library by 1st, 2nd and 3rd year undergraduates of Faculty of Science, University of Kelaniya. The objectives of this study are to assess the usage and usage patterns of the students of Faculty of Science, University of Kelaniya. The study focused on estimating the average time of library usage, investigate the average number of books read by students per month, identify in which stream students use the library most, understand the reasons and periods in which students access the library most, and estimate their overall satisfaction on the main library. The data required for the study was collected through a survey that was conducted during the period of September – December 2016. Among the 1670 students registered in the Faculty of Science, 197 respondents were randomly selected using stratified random sampling method (without replacement) by considering students’ education streams as strata. After an initial pilot survey was conducted, questionnaires were distributed among the 197 respondents. The collected data were analysed using a statistical software to meet the objectives. Eighty seven percent of the students of the Faculty of Science use the main library whereas highest number of students (90%) using the library was from the Biological Science stream. The average library usage time of a student is about 2 hours per week. The average number of books used by students per month is two books. The main reason to use the library by the students is for studying their lecture notes and second reason is to read additional reading materials. Students use the library least at the beginning of the semester and widely use the library during the study-leave period. Reasons cited for reluctance to use the university library by the students who do not use the library, were lack of free time and the administrative rules of the library. Majority of the students (70%) use the university main library whereas few of the students use other libraries. It was also found that approximately 51% of the undergraduates of Faculty of Science were satisfied about the facilities provided by the university main library. The results of this survey will be useful to understand the usage of main library by the students of Faculty of Science in order to assist the administration to, further improve the productive use of its resources.
A Univariate Box-Jenkins Model to Predict Relative Humidity Levels in Puttalam at Night
(University of Kelaniya, 2008) Attanayake, A.M.C.H.; Hewapathirana, T.K.
Humidity is among one of the most important weather conditions that influence salt preparation. Technical processes and treatments carried out in salt factories and laboratories require relative humidity levels to be maintained using control systems. Puttalam is a reputed saltern in Sri Lanka. The knowledge on the fluctuations of relative humidity is paramount for the management of Puttalam saltern, to carry out their activities in a proper manner. This paper presents the results of a study carried out to develop a prediction model for relative humidity during night time in Puttalam saltern, using Box-Jenkins methodology. This study is based on percentage mean relative humidity data collected from the Puttalam weather station from January 1998 to December 2007. Sample autocorrelation functions and sample partial autocorrelation functions are used as the major diagnostic tools in this model building procedure. Model parameters were estimated using the non-linear least squares method. The adequacy of the fitted model was checked by analyzing the residuals. According to the analysis it was revealed that the ARIMA (1, 0, 1) (1, 1, 1\2 model is the best model that could be used to forecast the percentage mean relative humidity at Puttalam saltern during night time. Forecasts can be readily generated using the above model up to a period of twelve months without using any external variables.
Vaccination Coverage for COVID-19 in Sri Lanka: With and Without Age Stratification on Susceptible-Infectious-Recovered Simulation
(Journal of Occupational Health and Epidemiology,, 2022) Attanayake, A.M.C.H.
Background: Vaccination against COVID-19 is as a key solution to interrupt its spread. This study aimed to describe the vaccination coverage required to stop the spread of COVID-19 in Sri Lanka using a mathematical modeling strategy. Materials & Methods: This longitudinal study used age-stratified and unstratified Susceptible-Infectious-Recovered (SIR) models. Data on the population's age distribution were acquired from the census report of the Census and Statistics Center of Sri Lanka, consisting of groups: below 30, between 30-59, and over 60. Models with differential equations forecasted the spread of COVID-19 with vaccination based on parameter estimates and numerical simulation, assuming fixed population, infection, and recovery rates. Results: Simulations investigated how the susceptible, infected, and recovered populations varied according to the different vaccination coverages. According to the results, 75% vaccination coverage was required in the entire population of Sri Lanka to interrupt the transmission of COVID-19 completely. The age-stratified SIR model showed that over 90% of vaccination coverage in each age group (below 30, between 30-59, and over 60) was required to interrupt the transmission of COVID-19 in the country altogether. Conclusions: The number of COVID-19 infections in each age group of Sri Lanka reduces with the increase in vaccination coverage. As 75% vaccination coverage is required in Sri Lanka to interrupt the transmission of the disease, precise vaccination coverage measurement is essential to assess the successfulness of a vaccine campaign and control COVID-19.