Search results for "selection bias."
showing 10 items of 49 documents
Estimating the non-market benefits of water quality improvement for a case study in Spain: A contingent valuation approach
2012
Abstract This article addresses an important topic related to the application of the European Water Framework Directive (WFD) in Spanish watersheds. Results on a contingent valuation study, aimed to assess the non-market benefits of water quality improvements in the Guadiana river basin (GRB), are shown. Special attention has been paid to the issue of zero willingness-to-pay (WTP) responses, while addressing the possible presence of self-selection caused by protest responses. The results (i) indicate that sample selection bias is not a problem in our application, (ii) allow us to identify some key determinants of voting behaviour, and (iii) through the use of different econometric models al…
Effects of Grade Retention Policies: A Literature Review of Empirical Studies Applying Causal Inference
2021
The identification of the causal effects of grade retention policies is of enormous relevance for researchers and policymakers alike. Taking advantage of the availability of more detailed longitudinal datasets, researchers have been able to apply different identification strategies that address the classical problems of selection bias and unobserved heterogeneity that have plagued previous studies on the effect of retention. We present a systematic literature review of empirical studies aiming to unveil the causal effects of retention. This study underlines the need to consider and evaluate different kinds of grade retention polices as their effects vary depending on several dimensions (suc…
Familial HDL deficiency due to ABCA1 gene mutations with or without other genetic lipoprotein disorders
2004
Mutations in ABCA1 have been shown to be the cause of Tangier disease (TD) and some forms of familial hypoalphalipoproteinemia (HA), two genetic disorders characterized by low plasma HDL levels. Here we report six subjects with low HDL, carrying seven ABCA1 mutations, six of which are previously unreported. Two mutations (R557X and H160FsX173) were predicted to generate short truncated proteins; two mutations (E284K and Y482C) were located in the first extracellular loop and two (R1901S and Q2196H) in the C-terminal cytoplasmic domain of ABCA1. Two subjects found to be compound heterozygotes for ABCA1 mutations did not have overt clinical manifestations of TD. Three subjects, all with prema…
Comorbidity between obesity and attention deficit/hyperactivity disorder: Population study with 13–15-year-olds
2006
Objective: This study analyzes whether obese children have a higher risk of attention deficit/hyperactivity “characteristics” (AD/HD) than do children with other nutritional states. Method: This study included 35,403 participants from 486 community schools. They completed the AD/HD scale of the Strengths and Difficulties Questionnaire (SDQ) and were weighed and measured. 2879 of the participants were obese and 78 were morbidly obese (BMI >40). Results: A discrete, nonsignificant, increment was found in the AD/HD characteristics of male participants with morbid obesity, as compared with the other nutritional states. Among morbidly obese females, the prevalence of AD/HD characteristics was sl…
Investigating the association between cancer and the risk of dementia: Results from the Memento cohort
2021
International audience; IntroductionStudies on the association of cancer and risk of dementia are inconclusive due to result heterogeneity and concerns of survivor bias and unmeasured confounding.MethodsThis study uses data from the Memento cohort, a French multicenter cohort following persons with either mild or isolated cognitive complaints for a median of 5 years. Illness‐death models (IDMs) were used to estimate transition‐specific hazard ratios (HRs) and 95% confidence intervals (CIs) for incident cancer in relation to dementia from time since study entry.ResultsThe analytical sample (N = 2258) excluded 65 individuals without follow‐up information. At the end of follow‐up, 286 individu…
The categorization of amateur cyclists as research participants: findings from an observational study.
2018
Sampling bias is an issue for research involving cyclists. The heterogeneity of cyclist populations, on the basis of skill level and riding purpose, can generate incorrect inferences about one specific segment of the population of interest. In addition, a more accurate categorization would be helpful when physiological parameters are not available. This study proposes using self-reported data to categorize amateur cyclist types by varying skill levels and riding purposes, therefore improving sample selection in experimental studies. A total of 986 cyclists completed an online questionnaire between February and October 2016. Two-step cluster analyses were performed to generate distinct group…
On the value of drovers’ routes as environmental assets: A contingent valuation approach
2013
The aim of this study was to evaluate the non-market benefits resulting from the restoration of an old drovers’ route for recreation uses in Valencia (Spain). The valuation was carried out using the Contingent Valuation Method (CVM) through the elicitation of individuals’ willingness to pay (WTP). Since 52% of the respondents stated a zero WTP response, in order to inform decision-making processes more accurately, special attention was paid to the problem of zero and protest responses, and also to the possible presence of self-selection by those that protested. For the different specifications considered, results suggest that mean WTP estimates are higher for “rural areas” than for “the Val…
Inter-industry job mobility in the knowledge economy in Finland
2013
Purpose – The purpose of this paper is to investigate inter-industry labor mobility, paying special attention to workers who move into high-tech (HT) sectors or knowledge-intensive business services (KIBSs). This study inquires whether skilled workers are mobile and whether the characteristics of mobile workers support the effective transfer of knowledge across industries. Design/methodology/approach – Census data representing 7 percent of Finnish residents were used. The micro-econometric estimation method with correction of sample selection bias was applied. Findings – The results show that young workers are the most mobile, whereas mobility decreased for those with previous work experie…
A comparison of two indirect methods for estimating average levels of gene flow using microsatellite data.
1999
We compare the performance of Nm estimates based on FST and RST obtained from microsatellite data using simulations of the stepwise mutation model with range constraints in allele size classes. The results of the simulations suggest that the use of microsatellite loci can lead to serious overestimations of Nm, particularly when population sizes are large (N5000) and range constraints are high (K20). The simulations also indicate that, when population sizes are small (N/= 500) and migration rates are moderate (Nm approximately 2), violations to the assumption used to derive the Nm estimators lead to biased results. Under ideal conditions, i.e. large sample sizes (ns/= 50) and many loci (nl/=…
Informal employment in developing countries
2012
There is an ongoing debate among researchers and policy makers, whether informal sector employment is a result of competitive market forces or labor market segmentation. More recently it has been argued that none of the two theories sufficiently explains informal employment, but that the informal sector shows a heterogenous structure. For some workers the informal sector is an attractive employment opportunity, whereas for others – rationed out of the formal sector – the informal sector is a strategy of last resort. To test the empirical relevance of this hypothesis we formulate an econometric model which allows for several unobserved segments within the informal sector and apply it to the …