anzctr.org.au Identifier: ACTRN12605000658617; isrctn.org Identifier: ISRCTN83409867.

Objective: To compare different statistical methods for assessing the relative validity of a self-administered, 150-item, semi-quantitative food-frequency questionnaire (FFQ) with 4-day weighed diet records (WR). Design: Subjects completed the Scottish Collaborative Group FFQ and carried out a 4-day WR. Relative agreement between the FFQ and WR for energy-adjusted nutrient intakes was assessed by Pearson and Spearman rank correlation coefficients, the percentages of subjects classified into the same and opposite thirds of intake, and Cohen's weighted kappa. Subjects: Forty-one men, mean age 36 (range 21-56) years, and 40 women, mean age 33 (range 19-58) years, recruited from different locations in Aberdeen, Scotland. Results: Spearman correlation coefficients tended to be lower than Pearson correlation coefficients, and were above 0.5 for 10 of the 27 nutrients in men and 17 of the 27 nutrients in women. For nutrients with Spearman correlation coefficients above 0.5, the percentage of subjects correctly classified into thirds ranged from 39 to 78%, and weighted kappa values ranged from 0.23 to 0.66. Conclusions: Both Spearman correlation coefficients and weighted kappa values are useful in assessing the relative validity of estimates of nutrient intake by FFQs. Spearman correlation coefficients above 0.5, more than 50% of subjects correctly classified and less than 10% of subjects grossly misclassified into thirds, and weighted kappa values above 0.4 are recommended for nutrients of interest in epidemiological studies. Keywords Correlation coefficientsKappa statistic Food-frequency questionnaire Relative validity Weighed diet records Epidemiological methods Dietary assessmentThe semi-quantitative food-frequency questionnaire (FFQ) is the primary dietary assessment method used in epidemiological studies 1. Results from such studies can be interpreted with greater confidence if the questionnaire has a quantified validity; i.e. the ability of the questionnaire to measure what it is intended to measure. To assess the true validity of an FFQ would require measuring with high accuracy the usual self-selected diet of freeliving individuals over several months, which is not feasible. Therefore, researchers assess relative validity by comparing the FFQ with an alternative dietary assessment method with its own limitations.In epidemiological studies, the odds ratio or relative risk of disease in relation to nutrient intake is the most common measure of association presented. Consequently, FFQs must be able to rank individuals along the distribution of intake, so that individuals with low intakes can be separated from those with high intakes. Therefore, obtaining absolute nutrient intakes is not necessary. As long as FFQs can rank individuals, relative risk estimates will be accurate 2 . The usual method of assessing agreement in ranking between an FFQ and a reference method is to calculate Pearson correlation coefficients for log e -transformed data or Spearman rank correlation coefficients for data that are not n...

Abstract. The factors contributing to anemia in falciparum malaria were characterized in 4,007 prospectively studied patients on the western border of Thailand. Of these, 727 patients (18%) presented with anemia (haematocrit Ͻ 30%), and 1% (55 of 5,253) required blood transfusion. The following were found to be independent risk factors for anemia at admission: age Ͻ 5 years, a palpable spleen, a palpable liver, recrudescent infections, being female, a prolonged history of illness (Ͼ 2 days) before admission, and pure Plasmodium falciparum infections rather than mixed P. falciparum and Plasmodium vivax infections. The mean maximum fractional fall in hematocrit after antimalarial treatment was 14.1% of the baseline value (95% confidence interval [CI], 13.6-14.6). This reduction was significantly greater in young children (aged Ͻ 5 years) and in patients with a prolonged illness, high parasitemia, or delayed parasite clearance. Loss of parasitized erythrocytes accounted for Ͻ 10% of overall red blood cell loss. Hematological recovery was usually complete within 6 weeks, but it was slower in patients who were anemic at admission (adjusted hazards ratio [AHR], 1.9, 95% CI, 1.5-2.3), and those whose infections recrudesced (AHR, 1.2, 95% CI, 1.01-1.5). Half the patients with treatment failure were anemic at 6 weeks compared with 19% of successfully treated patients (relative risk, 2.8, 95% CI, 2.0-3.8). Patients coinfected with P. vivax (16% of the total) were 1.8 (95% CI, 1.2-2.6) times less likely to become anemic and recovered 1.3 (95% CI, 1.0-1.5) times faster than those with P. falciparum only. Anemia is related to drug resistance and treatment failure in uncomplicated malaria. Children aged Ͻ 5 years of age were more likely than older children or adults to become anemic. Coinfection with P. vivax attenuates the anemia of falciparum malaria, presumably by modifying the severity of the infection.

A systematic review and meta-analysis examining the association between anti-merozoite antibody responses and incidence of Plasmodium falciparum malaria by Freya Fowkes and colleagues aids identification of antigens that confer protection from malaria.

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