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SIENA (for Simulation Investigation for Empirical Network Analysis) is a computer program that carries out the statistical estimation of models for the evolution of social networks according to the dynamic actor-oriented model of Snijders (2001, 2003) and Steglich, Snijders and Pear-son (2004). It also carries out MCMC estimation for the exponential random(More)
In this paper we both describe and analyze the meeting process and the evolution of a friendship network among sociology freshmen in the Netherlands. We develop a theory that explains how changes in the network structure depend on one or more of four main effects: proximity, visible similarity, invisible similarity, and network opportunity. We formulate(More)
The collection of longitudinal data on complete social networks often faces the problem of actor non-response. The resulting incomplete data pose a challenge to statistical analysis, as there typically is no natural way to treat the missing cases. This paper examines the problems caused by actors missing as nominators, but still occurring as nominees, in(More)
OBJECTIVE To assess the frequency and phenotype of hexanucleotide repeat expansions in C9ORF72 in a large cohort of patients of Dutch descent with familial (fALS) and sporadic (sALS) amyotrophic lateral sclerosis (ALS), progressive muscular atrophy (PMA), and primary lateral sclerosis (PLS). METHODS Included were 78 patients with fALS, 1,422 with sALS,(More)
OBJECTIVE To investigate the association between cigarette smoking, level of education, occupation, and the occurrence of sporadic amyotrophic lateral sclerosis (ALS). METHODS A total of 364 patients and 392 controls completed a questionnaire covering smoking habits, level of education, and occupational history. Main occupations were coded according to(More)
Analysis of social network data is often hampered by non-response and missing data. Recent studies show the negative effects of missing actors and ties on the structural properties of social networks. This means that the results of social network analyses can be severely biased if missing ties were ignored and only complete cases were analyzed. To overcome(More)
OBJECTIVES Reports of increased amyotrophic lateral sclerosis (ALS) with hyperlipidaemia and elevated plasma homocysteine levels as well as cigarette-smoking and polymorphisms in angiogenic genes suggest a role for altered vascular homeostasis in ALS pathogenesis. The authors assessed the association between vascular risk factors and ALS. METHODS(More)
Occupational and environmental exposures may contribute to the risk of developing sporadic amyotrophic lateral sclerosis (ALS). To summarize the available evidence, a systematic review of the literature on occupation as a potential determinant of ALS was performed according to the MOOSE guidelines. From MEDLINE, EMBASE, CINAHL, and Cochrane databases,(More)
BACKGROUND Amyotrophic lateral sclerosis shares characteristics with some cancers, such as onset being more common in later life, progression usually being rapid, the disease affecting a particular cell type, and showing complex inheritance. We used a model originally applied to cancer epidemiology to investigate the hypothesis that amyotrophic lateral(More)