Analyzing the influence of bigrams on retrieval bias and effectiveness

Prior work on using retrievability measures in the evaluation of information retrieval (IR) systems has laid out the foundations for investigating the relationship between retrieval effectiveness and retrieval bias. While various factors influencing bias have been examined, there has been no work examining the impact of using bigram within the index on retrieval bias. Intuitively, how the documents are represented, and what terms they contain, will influence whether they are retrievable or not. In this paper, we investigate how the bias of a system changes depending on how the documents are represented using unigrams, bigrams or both. Our analysis of three different retrieval models on three TREC collections, shows that using a bigram only representation results in the lowest bias compared to unigram only representation, but at the expense of retrieval effectiveness. However, when both representations are combined it results in reducing the overall bias, as well as increasing effectiveness. These findings suggest that when configuring and indexing the collection, that the bag-of-words approach (unigrams), should be augmented with bigrams to create better and fairer retrieval systems

Dietary fat intake, pesticide use, and Parkinson's disease

BACKGROUND: Dietary fat intake may modify Parkinson’s disease (PD) risk directly or by altering the response to environmental neurotoxicants including pesticides. METHODS: We conducted a case-control study of PD nested in the Agricultural Health Study (AHS), a cohort of pesticide applicators and spouses. We evaluated diet and pesticide use before diagnosis in 89 PD cases, confirmed by movement disorder specialists, or a corresponding date in 336 frequency-matched controls. Associations were evaluated using multivariate logistic regression to estimate odds ratios (ORs) and 95% confidence intervals (CIs). RESULTS: In the AHS, PD was inversely associated with N-3 polyunsaturated fatty acids (PUFAs) (OR 0.4,95% CI 0.2-0.8 for highest vs lowest tertile) and the N-3 precursor α-linolenic acid (0.4, 0.2-0.8). In a meta-analysis of nine studies, including the present one, PD was inversely associated with α-linolenic acid (0.81, 0.68-0.96). In the AHS, associations of PD with the pesticides paraquat and rotenone were modified by fat intake. The OR for paraquat was 4.2 (1.5-12) in individuals with PUFA intake below the median but 1.2 (0.4-3.4) in those with higher intake (p-interaction=0.10). The OR for rotenone was 5.8 (2.3-15) in those with saturated fat intake above the median but 1.5 (0.5-4.2) in those with lower intake p-interaction=0.02). CONCLUSIONS: PUFA intake was consistently associated with lower PD risk, and dietary fats modified the association of PD risk with pesticide exposure. If confirmed, these findings suggest that a diet high in PUFAs and low in saturated fats might reduce risk of PD