Generalized least squares can overcome the critical threshold in respondent-driven sampling

In order to sample marginalized and/or hard-to-reach populations, respondent-driven sampling (RDS) and similar techniques reach their participants via peer referral. Under a Markov model for RDS, previous research has shown that if the typical participant refers too many contacts, then the variance of common estimators does not decay like $O(n^{-1})$, where $n$ is the sample size. This implies that confidence intervals will be far wider than under a typical sampling design. Here we show that generalized least squares (GLS) can effectively reduce the variance of RDS estimates. In particular, a theoretical analysis indicates that the variance of the GLS estimator is $O(n^{-1})$. We then derive two classes of feasible GLS estimators. The first class is based upon a Degree Corrected Stochastic Blockmodel for the underlying social network. The second class is based upon a rank-two model. It might be of independent interest that in both model classes, the theoretical results show that it is possible to estimate the spectral properties of the population network from the sampled observations. Simulations on empirical social networks show that the feasible GLS (fGLS) estimators can have drastically smaller error and rarely increase the error. A diagnostic plot helps to identify where fGLS will aid estimation. The fGLS estimators continue to outperform standard estimators even when they are built from a misspecified model and when there is preferential recruitment.Comment: Submitte

Greener homes: Factors underpinning Europeans' intention to live in multi-storey wooden buildings

Climate policies aimed at curbing greenhouse gas emissions embodied in the built environment support the wider implementation of multi-storey wooden buildings. A body of research on public perceptions toward wood as a structural building material is emerging, but close examination of behavioral factors underpinning prospective dwelling is scarce. We used contextualized constructs from the theory of planned behavior to quantify and compare the roles of attitudes, subjective norms, and perceived behavioral control on intentions to dwell in multi-storey wooden buildings. Structural equation models were fitted to survey data from seven European countries (Austria, Denmark, Germany, Finland, Norway, Sweden, United Kingdom; n = 7056). We found that attitudes consistently explain intention to dwell in multi-storey wooden buildings. We also found a varied pattern of relationships between factors underpinning intention across countries. An implication of our results is that national-level policies aimed at promoting social acceptability of dwelling in multi-storey wooden buildings should universally address attitudes toward such novel buildings. But in some countries policies might in addition be tailored to emphasize citizens' subjective norms or perceived behavioral controls

Migration decision-making under environmental change: Place utility, mobility and ecosystem services in highland Peru

Migration is often conceptualised as a failure to adapt to environmental risks and change, while new research suggests migration is an effective front-line response to environmental degradation. This thesis investigates the social and environmental mechanisms that lead to individuals adopting migration as an adaptation to environmental change. It argues that the use of migration as a response to environmental change depends on the ecosystem services available at location, the mobility characteristics of the individual and the degree to which ecosystem contribute to place utility. I interpret place utility as a function of both instrumental and affective bonds to place. The research tests these ideas in a highland migrant sending area in a small coastal valley of Peru, geographically and culturally connected to the capital city Lima but predominantly rural in nature. The area has established rural-urban migration networks and a complex social-ecological system vulnerable to climate change. Data on mobility characteristics, contributors to place utility and use of ecosystem services in the rural sending area were collected through household surveys and semi-structured interviews. Four settlements were sampled along an altitudinal transect representing different ecological zones as well as different access to off-farm employment and other opportunities. Analysis of the primary data shows that individuals gain utility from non-provisioning ecosystem services independently of reliance on provisioning ecosystem services. These impacts of climate change that previously only had a cultural significance take on significance in terms of migration. The data show that individuals remain in location because of positive place utility or low mobility potential. I conclude that a likely result of environmental change is an increase in dissatisfaction with no significant changes in the composition of the population. Low mobility potential, a function of affective bonds to place, prevents dissatisfied people from migrating. The thesis shows that populations are likely to be persistent in the face of environmental change. Understanding why individuals remain in location reveals the viability of migration as an adaptation to environmental change

A hybrid approach for the analysis of complex categorical data structures: assessment of latent distance learning perception in higher education

A long tradition of analysing ordinal response data deals with parametric models, which started with the seminal approach of cumulative models. When data are collected by means of Likert scale survey questions in which several scored items measure one or more latent traits, one of the sore topics is how to deal with the ordered categories. A stacked ensemble (or hybrid) model is introduced in the proposal to tackle the limitations of summing up the items. In particular, multiple items responses are synthesised into a single meta-item, defined via a joint data reduction approach; the meta-item is then modelled according to regression approaches for ordered polytomous variables accounting for potential scaling effects. Finally, a recursive partitioning method yielding trees provides automatic variable selection. The performance of the method is evaluated empirically by using a survey on Distance Learning perception

O papel da orientação para o mercado no desempenho das empresas sociais

Market orientation has been presented as an important predictor of business performance. However, it is presumed to contribute to long-term success, both in commercial and nonprofit enterprises. Similarly, entrepreneurship orientation is a concept that has been widely applied to business firms but has not been empirically tested in social enterprises. Moreover, the literature does not present a widely accepted and tested conceptual model relating entrepreneurship orientation, market orientation and performance, in the realm of social enterprises. In order to fill this gap, this research assesses how these strategic orientations affect social and economic performance in the setting of social enterprises. Structural equation modelling was used as a means to analyze the hypothesized relationships. After testing the model on a sample of 805 Portuguese social enterprises, the findings show that both social entrepreneurship and market orientations significantly impact social performance. The results also indicate that market orientation mediates the effect of entrepreneurial orientation on the performance of social enterprises.A Orientação para o Mercado é um preditor importante do desempenho das empresas. No entanto, presume-se que contribua para o sucesso a longo prazo, tanto das empresas comerciais como das sem fins lucrativos. Igualmente, a orientação para o empreendedorismo é um conceito que tem sido amplamente aplicado às empresas, mas não tem sido empiricamente testado em empresas sociais. Mais a mais, a literatura não apresenta um modelo conceptual amplamente aceite e testado relacionando a orientação para o empreendedorismo, a orientação para o mercado e a performance, na realidade das empresas sociais. A fim de preencher esta lacuna, esta investigação avalia como essas orientações estratégicas afetam o desempenho social e económico no contexto das empresas sociais. A modelagem de equações estruturais foi utilizada como meio de analisar as relações que servem de base às hipóteses propostas. Depois de testar o modelo numa amostra de 805 empresas sociais portuguesas, os resultados mostram que ambas, a orientação para o empreendedorismo e para o mercado, afetam significativamente o desempenho das empresas sociais. Os resultados também indicam que a orientação para o mercado medeia o efeito da orientação empreendedora no desempenho das empresas sociais.Programa Doutoral em Marketing e Estratégi

Reducing edible food waste in the UK food manufacturing supply chain through collaboration

A thesis submitted to the University of Bedfordshire, in fulfilment of the requirements for the degree of Master of Philosophy.The aim of this study is to examine the relationship between food manufacturing supply chain (FMSC) collaboration, collaborative effectiveness and edible food waste (EF) waste reduction; and also identify the key dimensions of collaboration and collaborative effectiveness in the context of the FMSC. A conceptual framework was built based on thorough relevant literature review and theory. Then all items of the conceptual framework were revised by academics and practitioners. The model was empirically tested with survey data using 122 responses from food manufacturing firms, using PLS-SEM. The findings indicated that the structural paths support hypotheses that FMSC collaboration has a positive effect related to collaborative effectiveness, and collaborative effectiveness has a strong contribution in EF waste (over-production of EF waste, processing of EF waste and storage of EF waste) reduction. However, the direct impact of FMSC collaboration on EF waste (over-production of EF waste, processing of EF waste and storage of EF waste) reduction is insignificant. A mediation analysis showed that the relationship between FMSC collaboration and EF waste is fully mediated by collaborative effectiveness. This research brought relational view theory for the concept of FMSC collaboration and collaborative effectiveness into the FMSC context, which has not previously been done, and developed and validated those constructs and relationships. The UK FMSC members would benefit from applying all dimensions of FMSC collaboration in this study to their supply chain operation to achieve greater collaborative effectiveness, and that will lead to reducing EF waste