Search results for "12"
showing 10 items of 15303 documents
How many longitudinal covariate measurements are needed for risk prediction?
2014
Abstract Objective In epidemiologic follow-up studies, many key covariates, such as smoking, use of medication, blood pressure, and cholesterol, are time varying. Because of practical and financial limitations, time-varying covariates cannot be measured continuously, but only at certain prespecified time points. We study how the number of these longitudinal measurements can be chosen cost-efficiently by evaluating the usefulness of the measurements for risk prediction. Study Design and Setting The usefulness is addressed by measuring the improvement in model discrimination between models using different amounts of longitudinal information. We use simulated follow-up data and the data from t…
Model selection using limiting distributions of second-order blind source separation algorithms
2015
Signals, recorded over time, are often observed as mixtures of multiple source signals. To extract relevant information from such measurements one needs to determine the mixing coefficients. In case of weakly stationary time series with uncorrelated source signals, this separation can be achieved by jointly diagonalizing sample autocovariances at different lags, and several algorithms address this task. Often the mixing estimates contain close-to-zero entries and one wants to decide whether the corresponding source signals have a relevant impact on the observations or not. To address this question of model selection we consider the recently published second-order blind identification proced…
A new approach for estimating a nonlinear growth component in multilevel modeling
2011
This study presents a new approach to estimation of a nonlinear growth curve component with fixed and random effects in multilevel modeling. This approach can be used to estimate change in longitudinal data, such as day-of-the-week fluctuation. The motivation of the new approach is to avoid spurious estimates in a random coefficient regression model due to the synchronized periodical effect (e.g., day-of-the-week fluctuation) appearing both in independent and dependent variables. First, the new approach is introduced. Second, a Monte Carlo simulation study is carried out to examine the functioning of the proposed new approach in the case of small sample sizes. Third, the use of the approac…
Depressive symptoms during adolescence: Do learning difficulties matter?
2011
To examine whether learning difficulties play a role in depressive symptoms, 658 Finnish adolescents were asked to complete scales for depression three times during the transition to post-comprehensive education. They also reported on their learning difficulties and feelings of inadequacy as a student. The results showed that learning difficulties prospectively predicted depressive symptoms. Moreover, the impact of learning difficulties was mediated via inadequacy as a student: learning difficulties predicted feelings of inadequacy as a student which, in turn, contributed to greater increases in depressive symptoms. Finally, gender moderated the association between learning difficulties an…
Accuracy, Coherence, and Discrepancy in Self and Other Reports: Moving Toward an Interactive Perspective of Organizational Dissent.
2013
The purpose of this study was twofold and involved examining the viability of using the Organizational Dissent Scale as an other-report instrument, and developing additional perceptual data related to dissent expression. A sample of 291 people completed survey questionnaire measures of organizational dissent. Equal-sized groups ( n = 97) completed either a self-report, a workplace colleague other-report, or an organizational outsider other-report. Results indicated the Organizational Dissent Scale performed reliably as an other-report, but it showed some tendency for social desirability. In addition, findings suggested that certain indicators of proximity to the dissenter reduced discrepan…
Simultaneous optimization of harvest schedule and measurement strategy
2013
In many recent studies, the value of forest inventory information in the harvest scheduling has been examined. Usually only the profitability of measuring simultaneously all the stands in the area is examined. Yet, it may be more profitable to concentrate the measurement efforts to some subset of them. In this paper, the authors demonstrate that stochastic optimization can be used for defining the optimal measurement strategy simultaneously with the harvest decisions. The results show that without end-inventory constraints, it was most profitable to measure the stands that were just below the medium age. Measuring the oldest stands was not profitable at all. It turned out to be profitable t…
Fotogrammetrisen 3D-latvusmallin ja hyperspektriaineiston käyttö aluetason puustotulkinnassa
2017
Seloste artikkelista Tuominen S., Balazs A., Honkavaara E., Polonen I., Saari H., Hakala T., Viljanen N. (2017). Hyperspectral UAV-imagery and photogrammetric canopy height model in estimating forest stand variables. Silva Fennica vol. 51 no. 5 article id 7721. https://doi. org/10.14214/sf.7721
Dependency on un-captured GDP as a source of resilience beyond economic value in countries with advanced ICT infrastructure: Similarities and dispari…
2015
Abstract The majority of countries with advanced information and communication technology (ICT) infrastructure have been experiencing extended stagnation due to an “embedded” trap in ICT advancement. However, certain countries have been able to sustain a high level of ICT- driven global competitiveness. This suggests that in these contexts there is resilience beyond economic value. Finland and Singapore can be considered countries of resilience with respect to ICT-driven global competitiveness because of their continued GDP growth despite the recession. While both countries share significant similarities including institutional strength in ICT, they demonstrate noteworthy disparities in the…
Replacing Project Managers in Information Technology Projects
2015
According to anecdotal evidence, project managers working on information technology (IT) projects are occasionally replaced, although the literature on information systems (IS) and project management (PM) makes little mention of it. With a view to narrowing this knowledge gap the authors examined the reasons behind the practice. The authors took an interpretive approach to the data gathering and analysis, and collected descriptions about replacing project managers (RPM) from interviews and questionnaires (n=43). The concept of contradiction served as a lens through which to identify the underlying reasons. Contradiction refers to statements asserting or expressing the opposite of another st…
Twister Tries
2015
Many commonly used data-mining techniques utilized across research fields perform poorly when used for large data sets. Sequential agglomerative hierarchical non-overlapping clustering is one technique for which the algorithms’ scaling properties prohibit clustering of a large amount of items. Besides the unfavorable time complexity of O(n 2 ), these algorithms have a space complexity of O(n 2 ), which can be reduced to O(n) if the time complexity is allowed to rise to O(n 2 log2 n). In this paper, we propose the use of locality-sensitive hashing combined with a novel data structure called twister tries to provide an approximate clustering for average linkage. Our approach requires only lin…