Quantifying and addressing the prevalence and bias of study designs in the environmental and social sciences.

Building trust in science and evidence-based decision-making depends heavily on the credibility of studies and their findings. Researchers employ many different study designs that vary in their risk of bias to evaluate the true effect of interventions or impacts. Here, we empirically quantify, on a large scale, the prevalence of different study designs and the magnitude of bias in their estimates. Randomised designs and controlled observational designs with pre-intervention sampling were used by just 23% of intervention studies in biodiversity conservation, and 36% of intervention studies in social science. We demonstrate, through pairwise within-study comparisons across 49 environmental datasets, that these types of designs usually give less biased estimates than simpler observational designs. We propose a model-based approach to combine study estimates that may suffer from different levels of study design bias, discuss the implications for evidence synthesis, and how to facilitate the use of more credible study designs.

Incisive structure-spectroscopic correlation in oligothiophenes functionalized with (+/-) inductive/mesomeric fluorine groups: joint Raman and DFT study.

This paper presents a combined experimental Raman and density functional theory (DFT) study of a series of oligothiophenes with variable pi-core lengths and substituted at the alpha,omega- and beta,beta'-terminal positions with perfluorohexyl, perfluorohexylcarbonyl, perfluoroarene, and cyano groups. The study covers the neutral and the electrochemically oxidized samples. The spectra have been assigned with the help of B3LYP/6-31G** calculations and interpreted by the predictions of effective conjugation coordinate (ECC) theory. Direct relationships between the bond length alternation (BLA) parameters and the Raman wavenumbers of the two most important bands of the spectra have been outlined showing the collective character of their electronic and vibrational properties. It is found that the topology of the thienyl electronic structure is not uniform along the conjugated core with the external rings more aromatic, whereas for the innermost part the pi-electron delocalization is greater and extends with the increment of chain length. Perfluorohexyl substitution finely tunes the electronic properties via negative inductive effects. The beta,beta' isomers exhibit larger conformational distortion, which strongly modifies the mean conjugation length. Oxidation provokes electronic structure quinoidization spreading over the whole system but more marked in the central part of the pi-core. The Raman features associated to quinoidization in the oxidized species have been interpreted in relation to the oligomer core length and the substitution regiochemistry.