Browsing by Author "Wijesuriya, B.W."

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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.
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.
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.
Use of covariates in improving precision of field experiments in rubber
(Postgraduate Institute of Agriculture, University of Peradeniya:Peradeniya, 1996) Wijesuriya, B.W.; Thattil, R.O.