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A practical method to control spatiotemporal confounding in environmental impact studies.

ABSTRACT: Separating natural spatiotemporal variation from the impact of human activities has long been a challenge in environmental impact studies. To overcome this problem, a causal modelling method based on spatiotemporal data, integrated with existing statistical methods such as multivariate redundancy analysis, multiple regression and, ordination was used for inferring causal effects of wastewater on biotic ecosystems. The causal modelling techniques were structural equation modelling (SEM) and Bayesian Networks (BNs); SEM, with the help of statistical analysis, was used for building deterministic models while the composite hypothesis underlying the models was checked based on the principle of BNs. Both spatial and temporal variations were considered in the design of the study so that spatiotemporal confounding could be controlled by adjusting for 'time' and 'distance' in the models. This improved the external validity of the models, so they could be used for predicting the effect of interventions, e.g. manipulating the discharge loads. This could be possible where time-varying variables such as quantity of discharge effluent were included in the models. Models can be used for prediction the effect of an intervention in situations understood as causal. Thus, the causal structure of composite hypotheses of the study was tested using both local and global tests.

SUBMITTER: Hatami R

PROVIDER: S-EPMC6070679 | biostudies-literature | 2018

REPOSITORIES: biostudies-literature

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A practical method to control spatiotemporal confounding in environmental impact studies.

Hatami Rezvan R

MethodsX 20180705

Separating natural spatiotemporal variation from the impact of human activities has long been a challenge in environmental impact studies. To overcome this problem, a causal modelling method based on spatiotemporal data, integrated with existing statistical methods such as multivariate redundancy analysis, multiple regression and, ordination was used for inferring causal effects of wastewater on biotic ecosystems. The causal modelling techniques were structural equation modelling (SEM) and Bayes ...[more]

PMID: 30094200

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Project description:Numerous observational studies suggest that bisphosphonates reduce mortality. This study showed that bisphosphonate use is associated with lower mortality within days of treatment, although the association was not significant until the second week. Such an early association is consistent with confounding, although an early treatment effect cannot be ruled out.IntroductionThe purpose of this study was to examine whether confounding explains why numerous observational studies show that bisphosphonate use is associated with lower mortality. To this end, we examined how soon after treatment initiation a lower mortality rate can be observed. We hypothesized that, due to confounding, the association would be observed immediately.MethodsThis was a retrospective cohort study of hip fracture patients discharged from Swedish hospitals between 1 July 2006 and 31 December 2015. The data covered 260,574 hip fracture patients and were obtained from the Swedish Hip Fracture Register and national registers. Of the 260,574 patients, 49,765 met all eligibility criteria and 10,178 were pair matched (bisphosphonate users to controls) using time-dependent propensity scores. The matching variables were age, sex, diagnoses, prescription medications, type of hip fracture, type of surgical procedure, known or suspected dementia, and physical functioning status.ResultsOver a median follow-up of 2.8 years, 2922 of the 10,178 matched patients died. The mortality rate was 7.9 deaths per 100 person-years in bisphosphonate users and 9.4 deaths in controls, which corresponded to a 15% lower mortality rate in bisphosphonate users (hazard ratio 0.85, 95% confidence interval 0.79-0.91). The risk of death was lower in bisphosphonate users from day 6 of treatment, although the association was not significant until the second week.ConclusionBisphosphonate use was associated with lower mortality within days of treatment initiation. This finding is consistent with confounding, although an early treatment effect cannot be ruled out.

Dataset Information

A practical method to control spatiotemporal confounding in environmental impact studies.

Publications

A practical method to control spatiotemporal confounding in environmental impact studies.

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