One size does not fit all: Heterogeneous economic impact of integrated pest management practices for mango fruit flies in Kenya—a machine learning approach

Most previous studies evaluating agricultural technology adoption focus on estimating homogeneous average treatment effects across technology adopters. Understanding the heterogeneous effects and drivers of impact heterogeneity should enable interventions to be better targeted to maximise benefits. We apply machine learning using data from a randomised controlled trial to estimate the heterogeneous treatment effect of fruit fly IPM practices (i.e., parasitoids, orchard sanitation, use of food bait, biopesticides, male annihilation technique, and their combinations) in Central Kenya. Results suggest significant heterogeneity in the effect of IPM practices conditioned on household characteristics. The most important covariates explaining differences in treatment effects are wealth, distance to the mango fruit market, age of the household head, labour and experience in mango farming. Results further indicate that those with fewer mango trees benefit more from most IPM practices. Additional analysis across other covariates shows mixed results but generally suggests significant differences between households benefiting the most and those benefiting the least from IPM practices.     

A proof of asymptotic normality for some VARX models

Here we present a proof of the asymptotic normality of least squares estimates for stable multivariate autoregressive models excited by a deterministic second order input signal.     

On the feasibility of monetary union among Gulf Cooperation Council (GCC) countries: does the symmetry of shocks extend to the non-oil sector?

GCC countries’ output is heavily dichotomized into oil and non-oil. Oil shocks have similar effects on all member countries but little is known about their responses to non-oil shocks. This paper sets out to determine (1) whether aggregate demand (AD) and non-oil supply shocks (AS) are symmetrical across these countries to justify their suitability for monetary union; and (2) whether there is any commonality of shocks with the United States and the three major European countries, namely France, Germany, and Italy, which can warrant the choice of either the US dollar or the Euro as the anchor for the expected common currency of the bloc. We use bivariate structural vector autoregression models identified with long-run restrictions to extract the shocks. Our results show that (a) AD shocks are unequivocally symmetrical but non-oil AS shocks are weakly symmetrical across GCC countries thereby suggesting a monetary union is feasible, but not overwhelmingly; (b) neither AD nor AS shocks are symmetrical between GCC countries and the selected European countries; (c) GCC’s AD shocks are symmetrical with the US but non-oil AS shock are not. Furthermore, there are no significant changes in the results when we aggregate the GCC countries as a bloc. We therefore surmise that the US dollar is a more appropriate anchor for the new currency than the Euro since US monetary policy can at least help smooth demand shocks in GCC countries.     

Malmquist indices of productivity growth for Islamic and conventional banks in Malaysia

This paper studies the total factor productivity （TFP） of banks in Malaysia with the emphasis on comparing the relative productivities of Islamic and Conventional banks. The Malmquist index approach is used to decompose productivity growth into technical efficiency and technological change. The productivity growth is measured and decomposed into technical change and efficiency change. The efficiency change is further decomposed into pure efficiency change and scale efficiency. It is found that Islamic banks＇ productivity growth is limited by its lack of technological change compared to its conventional counterparts. Nonetheless, both types of banks are operating at the correct level in terms of scale or size.     

An engineering approach to LSE modelling of experience curves in the electricity supply industry

This review is a supplement to the paper by Sharp and Price (1990) and should be regarded as an alternative engineering approach to the modelling and forecasting of experience, or learning, curves. It highlights the problems associated with accurately defining a model to time series that show a combination of a continuous trend and a cyclical component, as detected by the authors in the Sharp and Price data. The authors give a number of alternative perspectives of the same time series, in this case average thermal efficiency data from the U.K. electricity supply industry, with the corresponding conclusions associated with each approach. Particular attention is drawn to the use of the “time constant learning curve” quoted by Sharp and Price which the authors show is a reasonable predictor of the average thermal efficiency. However, a tremendous improvement results from selecting the “ripple” model as a thermal efficiency predictor.     

Pooling surveys in the estimation of income and price elasticities: An application to Tunisian households

This paper presents a methodological extension of Deaton's (1990) model for estimating price elasticities, by pooling Tunisian data from several surveys to improve the inter-cluster variability of unit values which is one of the key elements used in the derivation of these elasticities. Since the surveys cover a relatively long period, possible structural changes in consumption behaviour occurring over time are accounted for by postulating that certain response coefficients of the basic model vary from one survey to the other. The own price and cross price elasticities calculated using appropriate estimates of the extended model are satisfactory both from the economic point of view of their sign and the statistical point of view of their significance and superior to those obtained using a single survey. First version received: April 2000/Final version received: June 2001 RID="*" ID="*"  The authors would like to thank Angus Deaton and anonymous referees for useful comments and suggestions.     

Accounting and stock market effects of international accounting standards adoption in an emerging economy

This study examines the impact of the mandatory adoption of the 1997 and 2006 Egyptian accounting standards on earnings quality and firm valuation. Extant research finds that IAS-based standards have positive effects on financial statement attributes (e.g., earnings management) and capital market-related variables (e.g., firm valuation) in some countries, and negative or neutral effects in others. Research conducted in this area on emerging markets is scant, and none in Egypt, which has adopted in 1997 an IAS-based standards (later revised twice in 2002 and 2006). Using a sample of Egyptian listed firms around the time of introducing the 1997 and 2006 EAS versions, I find insignificant empirical evidence that earnings management decreases post adoption of each of the EAS versions under investigation. Additionally, I find that firm valuation (Tobin’s q) was significantly negatively affected by both EAS versions under investigation in this study. I attribute these results to the lack of compliance by financial statement preparers, improper regulatory enforcement mechanisms, the poor accounting infrastructure, and the inadequate practitioner training, claimed by prior literature.     

Returns from research in economies with policy distortions: hybrid sorghum in Sudan

Conventional estimates of the economic return to agricultural research use market prices for the values of products and inputs; on this basis, economic rates of return are typically well above the cost of capital, suggesting that more investment in research would be socially desirable. But these estimates may be incorrect if, as is often the case, market prices are distorted by market failures or government policies and hence do not reflect social values. This paper presents a simple, partial-equilibrium methodology with which to improve the measurement of social returns to research by taking account of multiple distortions in the market prices of products, inputs and foreign exchange. The method also takes account of variation in domestic and world prices, making a product tradable in some years and nontradable in others. The method is applied to the case of Hageen-Dura 1 (HD-1), Sub-Saharan Africa's first commercially successful hybrid sorghum. HD-1 was released in the Sudan in 1983. From the start of research in 1979 to 1992, the HD-1 breeding program had an estimated IRR of 97% when all major policies in the sorghum market, the fertilizer market, and the exchange rate are taken into account. The high rate of return to HD-1 research was due to the program's low cost and rapid payoff, pointing to the potential value of small adaptive research programs, taking full advantage of foreign technology and genetic material to produce locally-appropriate crosses in a short period of time. Even in the highly distorted economies of Africa, such programs can yield very high payoffs.     

The difficulties of evaluating sales training

Practitioners and researchers acknowledge the importance of sales training; however, limited attention is devoted to empirical sales training evaluation practices. This article addresses four major sources of sales training evaluation difficulties: (1) managerial perceptions; (2) evaluation restrictions; (3) methodological problems; and (4) lack of empirical evidence. After discussing each area, managers are provided with suggestions that can be implemented to minimize sales training evaluation problems.     

On leanness, agility and leagile supply chains

In 1999 a paper by Naylor, Naim and Berry on ‘leagility’ was published in international journal of production economics. The paper has attracted over 100 independent citations from over 60 journals of international standing. This paper explores the testing, exploitation and extension of the original work. Via a systematic literature review the notable findings are that the 1999 paper has been exploited in terms of its classification of supply chains into lean, agile and ‘leagile’; those terms have been tested via survey and case based empirical research; has been extended beyond the original stock decoupling point exploitation of lean and agile to encompass other forms of ‘leagility’. This paper concludes that further robust testing of ‘leagility’ and the definitions of leanness and agility are still required to encompass different market sectors and ensure triangulation of research methods.