Data from longitudinal surveys give rise to many statistical challenges. They often come from a vast, heterogeneous population and from a complex sampling design. Further, they are usually collected retrospectively at intermittent interviews spaced over a long period of time, which gives rise to missing information and loss to follow-up. As a result, duration data from this kind of surveys are subject to dependent censoring, which needs to be taken into account to prevent biased analysis. Methods for point and variance estimation are developed using Inverse Probability of Censoring (IPC) weights. These methods account for the random nature of the IPC weights and can be applied in the analysis of duration data in survey and non-survey settings. The IPC estimation techniques are based on parametric estimating function theory and involve the estimation of dropout models. Survival distributions without covariates are estimated via a weighted Kaplan-Meier method and regression modeling through the Cox Proportional Hazards model and other models is based on weighted estimating functions. The observational frameworks from Statistics Canada's Survey of Labour and Income Dynamics (SLID) and the UK Millenium Cohort Study are used as motivation, and durations of jobless spells from SLID are analyzed as an illustration of the methodology. Issues regarding missing information from longitudinal surveys are also discussed.

Introduction. There is ample evidence that using carbohydrates during physical exercise contributes to increasing the duration of the physical load being experIenced. Still research devoted to the study of using carbohydrate solutions of different concentrations and in different quantities is of great interest. No definite results as to the time of assimilation of carbohydrates in respect to the starting point of the physical load undertaken are available either. Carbohydrates are the main source of energy during intensive exercise. The body of the athlete requires a greater amount of carbohydrates since they present in themselves the most efficient source of energy that prolongs muscle function by providing possibilities for the energy to be generated both aerobically and anaerobically. The topicality of the present study lies in the fact that it is aimed at establishing the effect of different solutions on the working capacity of athletes. The hypotesis of the research is: the assimilation of extra glucose 20 min after the start of running helps to prolong the duration of running. The aim of the research done was to establish the effect of using glucose during running on the duration of running possible. Subjects and methods. The subjects were seven long – distance runners (age 23.0 ± 1.9 years, height 1.82 ± 2.7 m, weight 77.0 ± 7.85 kg and body mass index 23.79 ± 2.06 kg/m2). Information as to health condition of the subjects, their physical activity and nutrition was... [to full text]

Background: Health Canada recommends exclusive breastfeeding for the first 6 months postpartum with continued breastfeeding up to 2 years and beyond. While 88% of Canadian mothers initiate breastfeeding, only 70% of mothers continue to do so at 4 weeks postpartum and only 14% are exclusively breastfeeding at 6 months. Breastfeeding self-efficacy is a potentially modifiable variable that has been associated with mothers’ breastfeeding practices. The Breastfeeding Self-Efficacy Scale (Short-Form) is an instrument that could potentially identify women with low breastfeeding self-efficacy during the in hospital period. Purpose: To describe the breastfeeding practices of new mothers in the Kingston, Frontenac and Lennox & Addington area and to assess the association between in-hospital scores on the Breastfeeding Self-Efficacy Scale (Short-Form) and duration of breastfeeding. Methods: This study was a secondary analysis of a dataset from the 2008 Infant Feeding Survey, a prospective study of 463 mothers with 12-month longitudinal follow-up. Data were weighted according to the maternal age distribution of the general population of new mothers. Breastfeeding practices were described using Kaplan-Meier survival distributions. Four outcomes were described: ‘exclusive breastfeeding from birth’, ‘exclusive breastfeeding from discharge’, ‘high breastfeeding’, and ‘any breastfeeding’. Using logistic regression, scores from the Breastfeeding Self-Efficacy Scale (Short-Form) were assessed for association with duration of ‘exclusive breastfeeding from birth’ and duration of ‘any breastfeeding’ (dichotomized as ‘less than 6 weeks’ and ‘6 weeks or beyond’). Results: The sample was highly educated (75% had post-secondary education) and reported high levels of household income (37% reported >$80,000/year). Six percent of mothers exclusively breastfed to 6 months. Close to one quarter (24%) of women sustained some extent of breastfeeding for 12 months. The relationship between scores on the Breastfeeding Self-Efficacy Scale (Short-Form) and duration of ‘exclusive breastfeeding from birth’ and the relationship between self-efficacy scores and duration of ‘any breastfeeding’ were identical (OR = 1.05) and non-significant (95% CI 1.0-1.1). Conclusion: This study did not show a significant relationship between in-hospital scores on the Breastfeeding Self-Efficacy Scale (Short-Form) and duration of breastfeeding. Given the high socioeconomic status of women in this study, further studies are warranted to confirm these results. / Thesis (Master, Community Health & Epidemiology) -- Queen's University, 2011-12-06 14:46:41.103

The presented studies investigate dynamics of action potential duration (APD) tobetter understand the underlying mechanism for repolarization alternans.We recorded trans-membrane potentials (TMP) in canine endocardial muscle tissueusing standard glass microelectrode under the control of an explicit diastolic interval (DI)control pacing protocol, i.e. feedback protocol. During sequential sinusoidal DI activation,the trajectory of APD dynamics has multiple values of APD correspondent to the sameDI, i.e. restitution is a bi-modal relationship. Our results indicate that: 1) there is a delay,similar to hysteresis, of change in APD responding to change in DI, 2) and the timecourse of the delay is asymmetric for fast or slow pacing history. The alternans wasobserved during constant DI pacing, i.e. the DI preceding each APD was invariant orchanged within a limited range. This finding suggests that alternans of APD do not needthe oscillation of preceding DI, i.e. DI dependent restitution is not a necessary conditionfor the alternans. This result implies that DI independent component exists in themechanism of the alternans. Nonetheless, the amplitude of alternans was statisticallylarger during constant pacing cycle length (PCL) pacing than that during constant DIpacing, even though both PCL and DI pacing trials used similar average activation rate.These results also demonstrate the ability of the feedback protocol to analyze the memoryeffects and dissect different components in the mechanism of alternans.Two computational models, Luo-Rudy dynamics (LRD) and cardiac ventricle model(CVM) were used to study the hysteresis in restitution. By perturbing membrane current:L-type calcium current, rapid and slow potassium rectifier, and intracellular calciumtransfer rate in sarcoplasmic reticulum (SR) and using sinusoidal DI pacing sequence, weshowed that the asymmetric calcium current across the membrane and its interaction withcalcium buffer in SR during increasing and decreasing DI phase plays an important rolein the hysteresis. CVM was used to study the alternans during constant DI pacing.However CVM failed to replicate the alternans that occurred in the experiments. Thisresult implies that CVM lacks the electrophysiological kinetics related to alternans thatwas shown in our experiment.

This study adopts Markov-switching ARCH model proposed by Hamilton and Susmel (1994) to explore the behavior of credit spreads for different bond ratings. Specifically, this paper examines the properties of credit spreads and the co-movements of spreads among different durations and credit ratings. The consideration of the population makes the outcome more precise. The contribution of this study is to add to the investors a knowledge as to the credit spread behavior and help them understand the lower rating or longer maturity bonds by the observation of the investment-graded bonds while there are more risks and uncertainties conceal in these high yield bonds or D-rated bonds. The conclusion of this paper may help investors understand credit risk management and thus build appropriate portfolios.

Walking and bicycling to work, active commuting, can contribute to sustainable mobility and provide regular health-enhancing physical activity for individuals. Our knowledge of active commuting behaviours in general and in different mode and gender groups in particular is limited. Moreover, the validity and reproducibility of the methods to measure the key variables of the behaviours are uncertain. The aims of this thesis is to explore gender and mode choice differences in commuting behaviours in terms of distance, duration, velocity and trip frequency, of a group of adult commuters in Greater Stockholm, Sweden, and furthermore to develop a criterion method for distance measurements and to assess the validity of four other distance measurement methods. We used one sample of active commuters recruited by advertisements, n = 1872, and one street-recruited sample, n = 140. Participants received a questionnaire and a map to draw their commuting route on. The main findings of the thesis were, firstly, that the map-based method could function as a criterion method for active commuting distance measurements and, secondly, that four assessed distance measurement methods – straight-line distance, GIS, GPS and self-report – differed significantly from the criterion method. Therefore, we recommend the use of correction factors to compensate for the systematic over- and underestimations. We also found three distinctly different modality groups in both men and women with different behaviours in commuting distance, duration and trip frequency. These groups were commuters who exclusively walk or bicycle the whole way to work, and dual mode commuters who switch between walking and cycling. These mode groups accrued different amounts of activity time for commuting. Through active commuting per se, the median pedestrian and dual mode commuters met or were close to the recommended physical activity level of 150 minutes per week during most months of the year, whereas the single mode cyclists did so only during the summer half of the year.

Thesis (Ph. D.)--University of Missouri-Columbia, 2007. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on March 3, 2008) Vita. Includes bibliographical references.

Thesis (M.Eng.(Computer Engineering)--University of Pretoria, 2008. / Summaries in Afrikaans and English. Includes bibliographical references.

Thesis (M.S.)--Florida State University, 2005. / Advisor: Dr. Jie Chang, Florida State University, FAMU-FSU College of Engineering, Dept. of Electrical and Computer Engineering. Title and description from dissertation home page (viewed June 9, 2005). Document formatted into pages; contains xiii, 76 pages. Includes bibliographical references.

Thesis (Ph. D.)--Ohio State University, 2004. / Title from first page of PDF file. Document formatted into pages; contains xviii, 224 p.; also includes graphics. Includes bibliographical references (p. 199-211).