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The Effects of Market Reform on Maize Marketing Margins in South Africa: An Empirical Study AgEcon
Traub, Lulama Ndibongo; Jayne, Thomas S..
This paper determines the effect of market reform and price decontrol on the size of maize milling/retail margins in South Africa. Regression models of monthly milling/retail margins are run over the period May 1976 to September 2003. To assess the robustness of our findings, we estimate several different model specifications for representing structural change, vary the sample period to examine the sensitivity of findings to unusual weather and market conditions in the region during the 2001-2003 period, and use different estimation techniques, OLS with Newey-West robust estimators and Feasible General Least Squares. In virtually all models, the results indicate that real maize milling/retailing margins in South Africa have increased since the market...
Tipo: Conference Paper or Presentation Palavras-chave: Maize milling/retailing marketing margins; Market Reform; Ordinary Least Squares; Feasible General Least Squares.; Crop Production/Industries; Marketing.
Ano: 2006 URL: http://purl.umn.edu/25635
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OLS and Tobit Estimates: When is Substitution Defensible Operationally? AgEcon
Wilson, Clevo; Tisdell, Clement A..
Field data are used to illustrate that, other things constant, regression results using Ordinary Least Squares (OLS) converge to Tobit estimates as the number of zeros in the regressand decrease. Tobit estimates are theoretically superior to OLS estimates when using censored data. However, if little difference exists between OLS and Tobit estimates, OLS may be operationally acceptable. OLS may even be optimal in a bounded rationality sense because the extra cost of using Tobit analysis may be less than the extra benefits from a very slight increase in accuracy.
Tipo: Working or Discussion Paper Palavras-chave: Bounded rationality; Censored data; Ordinary Least Squares; Tobit; Regressand; Willingness to pay studies.; Public Economics.
Ano: 2002 URL: http://purl.umn.edu/90519
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