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LETTERS TO THE EDITOR
Reply to letter by Kusin et al. Dear Sir:
National Institute of Nutrition Indian Council of Medical Research Jamai-Osmania P. O. Hyderabad-500 007, A. P. India
The Lorstad model Dear Sir: Only very recently was my attention drawn to an article (1) that attributes various shortcomings to a general statistical model for the study of nutrient deficiencies, referred to as the Lorstad model. The pure statistical aspects of Reference 1 deserve a closer study in their own right, but since repeated references and comparisons are made with my model I would like to draw attention to the art of quoting references as exhibited in the article. The background for my original article (2), the purpose for which it was written and the assumptions for the model have not been adequately represented. Also, contributions (3, 4) relevant to the argument are not among the references. Background The Joint FAO/WHO Ad Hoc Expert Committee on Energy and Protein Requirements, convened in 1971, had before it numerous working papers. One of those pointed
out that an average intake, for a population, equal to a recommended intake did not imply that the requirements were met for all but a small proportion of individuals, but that instead the proportion of the population with below-requirement intake was somewhere in the range 25 to 35%. Reactions of some ofthe experts and study of reports of previous expert committees showed that the perfectly logical reason for this result was not fully appreciated. I was allowed, at the time an F AO staff member, to demonstrate for the Committee how the characteristics of a bivariate distribution for an intake/requirement model at the individual level would produce this result at the population level. The use of the model became a controversial issue during the year of finalization of the report of the Expert Committee and the d~ cision was made to make no reference to It (5). My efforts to publish the article in a nutrition scientific journal also outside F AO were fruitless, I like to believe for lack of persistence since I only tried once. The referee of the journal I had selected was of the opin-
Downloaded from https://academic.oup.com/ajcn/article-abstract/32/8/1562/4692259 by McMaster University Library user on 31 January 2019
We agree with Dr. Kusin that the rose Bengal test suggested for diagnosis of conjunctival xerosis has some limitations because the percentage of false positives is somewhat high. However, such cases will be few if the test is standardized well and only clear-cut and distinct patches visible from a distance of 1 m are considered positive. However, the percentage of false negatives was quite low in our experience. In the hospital study, only five children with serum vitamin A levels less than 20 Mg/dl showed a negative test. None of them had conjunctival xerosis and therefore, could not be detected even by clinical examination. Since the test is simple and has the advantage of being objective, paramedical personnel also can use the test for screening children
with conjunctival xerosis. In a survey' like this, it is inevitable that a certain proportion of cases of conjunctival xerosis not due to vitamin A deficiency will also be included. However, when weighed against the fact that some cases of vitamin A deficiency missed by clinical examination are detected by the dye test, inclusion of some with false positives may not vitiate the usefulness of the test. Vinodini Reddy Jr. Vijayaraghavan K V. R. Sharma P. Bhaskaram
LETTERS TO THE EDITOR
Reply to letter by Kusin et al. Dear Sir:
National Institute of Nutrition Indian Council of Medical Research Jamai-Osmania P. O. Hyderabad-500 007, A. P. India
The Lorstad model Dear Sir: Only very recently was my attention drawn to an article (1) that attributes various shortcomings to a general statistical model for the study of nutrient deficiencies, referred to as the Lorstad model. The pure statistical aspects of Reference 1 deserve a closer study in their own right, but since repeated references and comparisons are made with my model I would like to draw attention to the art of quoting references as exhibited in the article. The background for my original article (2), the purpose for which it was written and the assumptions for the model have not been adequately represented. Also, contributions (3, 4) relevant to the argument are not among the references. Background The Joint FAO/WHO Ad Hoc Expert Committee on Energy and Protein Requirements, convened in 1971, had before it numerous working papers. One of those pointed
out that an average intake, for a population, equal to a recommended intake did not imply that the requirements were met for all but a small proportion of individuals, but that instead the proportion of the population with below-requirement intake was somewhere in the range 25 to 35%. Reactions of some ofthe experts and study of reports of previous expert committees showed that the perfectly logical reason for this result was not fully appreciated. I was allowed, at the time an F AO staff member, to demonstrate for the Committee how the characteristics of a bivariate distribution for an intake/requirement model at the individual level would produce this result at the population level. The use of the model became a controversial issue during the year of finalization of the report of the Expert Committee and the d~ cision was made to make no reference to It (5). My efforts to publish the article in a nutrition scientific journal also outside F AO were fruitless, I like to believe for lack of persistence since I only tried once. The referee of the journal I had selected was of the opin-
Downloaded from https://academic.oup.com/ajcn/article-abstract/32/8/1562/4692259 by McMaster University Library user on 31 January 2019
We agree with Dr. Kusin that the rose Bengal test suggested for diagnosis of conjunctival xerosis has some limitations because the percentage of false positives is somewhat high. However, such cases will be few if the test is standardized well and only clear-cut and distinct patches visible from a distance of 1 m are considered positive. However, the percentage of false negatives was quite low in our experience. In the hospital study, only five children with serum vitamin A levels less than 20 Mg/dl showed a negative test. None of them had conjunctival xerosis and therefore, could not be detected even by clinical examination. Since the test is simple and has the advantage of being objective, paramedical personnel also can use the test for screening children
with conjunctival xerosis. In a survey' like this, it is inevitable that a certain proportion of cases of conjunctival xerosis not due to vitamin A deficiency will also be included. However, when weighed against the fact that some cases of vitamin A deficiency missed by clinical examination are detected by the dye test, inclusion of some with false positives may not vitiate the usefulness of the test. Vinodini Reddy Jr. Vijayaraghavan K V. R. Sharma P. Bhaskaram
