Browsing by Author "Thattil, R.O."

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Adjusting variables in constructing composite indices by using principal component analysis :illustrated by Colombo district data
(Postgraduate Institute of Agriculture, University of Peradeniya:Peradeniya, 2015) Dharmawardena, J.S.N.P.; Thattil, R.O.; Samita, S.
Alternative methods to determine plot sizes for tree crops. a case study from coconut data
(Coconut Research Institute of Sri Lanka. Lunuwila, 1997) Peiris, T.S.G.; Thattil, R.O.
Two methodologies are pooposed to determine the most efficient plot size for tree crops using data from experiments based on randomized complete block designs. Both methods can be generalized for data from any balanced design. The merits and demerits of these methods are discussed. The methods are illustrated using the data sets of long-term field ecperiments at the Coconut Research Institute, Sri Lanka. The results show that efficient plot size in field experiments for coconut for a wide range of agroecological regions is four or six palms.
An alternative model to estimate solar radiation
(Coconut Research Institute of Sri Lanka. Lunuwila, 1994-95) Peiris, T.S.G.; Thattil, R.O.
Solar radiation is extremely useful in modelling many agricultural applications, but is hardly used due to the difficulty in obtaining data, and the time consuming process in estimating it by the angstrom (1924) formula which uses world geographical relationships. To estimate solar radiation at the Coconut Research institute, Lunuwila (7o 20'N;71o 53'E;30.5m) an alternative model was developed from measured sunshine hours data only. The model had good fit (R2=0.90,P0.001) and was found to have agreement with the estimates obtained from the Angstrom model. The alternative model is more flexible and useful in estimating crop evapotranspiration, and for crop-weather modelling. The mean daily solar radiation at Lunuwila was estimated to be 18.3 MJ m-2d-1 and the total annual solar radiation receipts is 6680 MJ m-2 (66.8 TJ ha-1). The monthly solar radiation was highest in March (21.7MJ m-2 d-1) and the estimated 75 per cent probability value was 22.5 June had the lowest (16.1 MJ m-2 d-1) value and the estimated 75 per cent probability value was 17.8.
Analysis of growth and indirect selection for environmental sensitivity in Nicotiana rustica
(Postgraduate Institute of Agriculture, University of Peradeniya:Peradeniya, 1993) Thalib, A.T.L.; Kearsey, M.J.; Pooni, H.S.P.; Thattil, R.O.
Analysis of ranking exercises in participatory rural appraisal (PRA). a case study from the smallholder rubber sector
(Rubber Research Institute. Agalawatta, 2005) Wijesuriya, W.; Thattil, R.O.
Assessment of the effects of environmental factors on yield of coconut (Cocos nucifera L.)
(Coconut Research Institute of Sri Lanka. Lunuwila, 1997) Peiris, T.S.G.; Thattil, R.O.
The long term nut yield data and climate data of eight variables (1976-1992) were analyzed to understand the effects of climate and weather on the yield variability between picks. The yield variation over the years had no systematic pattern. The order of contribution of the picks to total yield is not significantly consistent between years. Explanatory models were developed at monthly lag periods prior to harvest of each pick. The most and least influential picks in respect of climate variability are picks 5 and 2 respectively. The critical period with respect to climate and weather variability of picks 1-6 are February , June July, Septermber, December and February respectively. The climatic models fitted at these periods explain the yield variability between picks. The influence of climatic variables during these periods vary from pick to pick. Maximum air temperature and relative humidity in the afternoon are the two most significant environmental variables influencing yield irrespective of picks.
Classification of geographical origin of Sri Lankan black tea using discriminant function analysis
(Postgraduate Institute of Agriculture, University of Peradeniya:Peradeniya, 2017) Peiris, T.U.S.; Walgampaya, C.K.; Thattil, R.O.; Abeysinghe, I.S.B.
Classification of state schools in Sri Lanka. a multivariate approach
(University of Peradeniya. Peradeniya, 2002) Dorabawila, S.S.K.B.M; Samita, S.; Thattil, R.O.
Control of variability in experiments with rubber using covariance technique. a review
(Rubber Research Institute. Agalawatta, 1997) Wijesuriya, B.W.; Thattil, R.O.
Comparatively little has been published on experimental techniques and statistical methods in rubber.This paper is a review of available literature on the use of covariates in experiments falling into immature and mature stages of rubber.The main objective is to encourage researchers to collect appropriate pre-treatment records to adjust the post.treatment variables so as to obtain high precision of results.In this connection,the effectiveness of rubber yield,girth and panel variables as pre-treatment records during the mature stages;seed and budded stump weights as covariates during the immature stages are discussed.The use of double covariance and other possible approaches to minimize initial variability in fertilizer,pest and disease,weed and green house experiments are also discussed.
Effect of some controllable parameters on optimization of characteristics in CTC type teas
(Postgraduate Institute of Agriculture, University of Peradeniya:Peradeniya, 1994) Ranaweera, A.S.; Thattil, R.O.; Basnayake, B.F.A.
Effect of temperature on optimum fermentation period for CTC type teas
(Postgraduate Institute of Agriculture, University of Peradeniya:Peradeniya, 1993) Ranaweera, A.S.; Thattil, R.O.; Basnayake, B.F.A.
An effective sampling procedure to estimate annual yield of rubber
(Postgraduate Institute of Agriculture, University of Peradeniya:Peradeniya, 1995) Wijesuriya, B.W.; Thattil, R.O.
Equal-weighted information criterion for model selection in univariate time series analysis
(Postgraduate Institute of Agriculture, University of Peradeniya:Peradeniya, 2015) Ankrah, S.; Peiris, B.L.; Thattil, R.O.
Estimation of food and nutrition factor in human development
(Postgraduate Institute of Agriculture, University of Peradeniya:Peradeniya, 2000) De Silva, A.P.G.S.; Thattil, R.O.; Samita, S.
Evaluation of ISO recommendation on analysis of precision experiments for statistical quality control
(Rubber Research Institute. Agalawatta, 1999) Wijesuriya, W.; Thattil, R.O.
Application of appropriate statistical methods is an important task in any quality control process as various statistical approaches such as;sampling,experimentationand process control are involved in quality control lprocesses.This has become an essential practice in many areas since the introduction of ISO quality assurance scheme .This article focuses on precision experiments where several laboratories are compared for a standard measurement method.The whole plrocess of analysis and interpretation suggested by ISO is evauated and documented in a sequential order.In addition to the ISO recommendation,additional graphical methods are suggested for better judgement .The statisticans role as a member of the panel is also lpresented at each step of the quality control process.
Evaluation of performance of public schools:an application of GIS in education surveys
(Postgraduate Institute of Agriculture, University of Peradeniya:Peradeniya, 2001) Satharasinghe, A.J.; Thattil, R.O.; Samita, S.; De Silva, R.P.
Factors associated with the adoption of the six row rice transplanter machine
(Postgraduate Institute of Agriculture, University of Peradeniya:Peradeniya, 1991) Niranjan, S.K.D.F.F.; Jayatilake, M.W.A.P.; Thattil, R.O.
Fertilizer response functions and optimum levels for bean cultivation in Badulla district
(Postgraduate Institute of Agriculture, University of Peradeniya:Peradeniya, 1999) Sivachandiran, S.; Thattil, R.O.; Samita, S.
Health status of primary schoolchildren in Sri Lanka
(Sri Lanka Medical Association. Colombo, 2005) Pathmeswaran, A.; Jayatissa, R.; Samarasinghe, S.; Fernando A.; De Silva, R.P.; Thattil, R.O.; De Silva, N.R.
Impact of production consumption, exports and stocks on the price of natural rubber in Sri Lanka
(Rubber Research Institute. Agalawatta, 1997) Wijesuriya, B.W.; Thattil, R.O.
The relationship between price of Natural Rubber (NR)with factors such as:production,consumption,exports and stocks are important in identifying the nature of competetion and therefore reveals the market structure for NR.This paper examines these relationships and also the seasonal variation of these factors,using time series statistical tools,viz Cross Correlation Functions (CCF)and seasonal indices. There is a marked seasonality in production with values below average during April to October (2nd and 3rd quarters).Prices tend to fall when the production rises.A similar phenomenon was observed between price and exports.However,the effect of production or exports on price is mild. A similar pattern of seasonal variation was observed for consumption and stocks of NR.More rubber is consumed during the latter part of the year.An accumulation of stocks was observed towards the end of the year.However,price of NR was not significantly related to consumption or stocks.This is mainly due to the fact that only a few buyers influence prices through their purchase and by adjustments of stocks as in an oligopolistic market.