Sample representativeness and influence of attrition on longitudinal data collected as part of a national medical career tracking project.

BACKGROUND: The Medical Schools Outcomes Database and Longitudinal Tracking Project (MSOD) in New Zealand is one example of a national survey-based resource of medical student experiences and career outcomes. Longitudinal studies of medical students are valuable for evaluating the outcomes of medical programs against workforce objectives. As a prospective longitudinal multiple-cohort study, survey response rates at each collection point of MSOD vary. This paper assesses the effects of participant non-response rates on MSOD data. METHODS: Demographic variables of MSOD respondents between 2012 and 2018 were compared to the distribution of the demographic variables in the population of all NZ medical graduates to ascertain whether respondent samples at multiple survey collection points were representative of the population. Analysis using logistic regression assessed the impact of participant non-response on variables at collection points throughout MSOD. RESULTS: 2874 out of a total population of 2939 domestic medical students graduating between 2012 and 2018 responded to MSOD surveys. Entry and exit surveys achieved response rates around 80% and were broadly representative of the total population on demographic variables. Post-graduation survey response rates were around 50% of the total population of graduates and underrepresented graduates from the University of Auckland. Between the entry and exit and the exit and postgraduation year three samples, there was a significant impact of non-response on ascribed variables, including age at graduation, university, gender and ethnic identity. Between the exit and postgraduation year one sample, non-response significantly impacted ascribed and non-ascribed variables, including future practice intentions. CONCLUSION: Samples collected from MSOD at entry and exit are representative, and findings from cross-sectional studies using these datasets are likely generalisable to the wider population of NZ medical graduates. Samples collected one and three years post-graduation are less representative. Researchers should be aware of this bias when utilizing these data. When using MSOD data in a longitudinal manner, e.g. comparing the change in career intentions from one collection point to the next, researchers should appropriately control for bias due to non-response between collection points. This study highlights the value of longitudinal career-tracking studies for answering questions relevant to medical education and workforce development.

Laser cooling of Yb3+:KYW.

We report the first observation of laser cooling in Yb3+:KYW and validate the results by comparison with experiments in the well-studied material Yb3+:YAG. Radiation from a single-mode Ti:Al2O3 laser was used to achieve cooling of 1.5 K/W in 1% Yb:KYW at 1025 nm, comparing well with the reference material 3% Yb:YAG which cooled by 3.5 K/W at 1030 nm under open lab conditions. Experimental results for KYW crystals mounted on aerogels and doped with 1-20% Yb were in excellent agreement with the theoretical dependence of cooling power on the Yb absorption spectrum. Elimination of thermal conduction through the sample support structure was found to permit the attainment of lower temperatures and to simplify modeling of radiation balance conditions in self-cooled lasers with longitudinal thermal gradients. Contrary to the notion that more coolant ions yield higher cooling power, concentrations of Yb over 1% caused re-absorption of luminescence in KYW crystals, leading to a progressive red shift in the optimal cooling wavelength and the prevention of laser cooling altogether in a 20% sample at room temperature. The prospect of attaining radiation-balanced lasing in commercially-available tungstate crystals is evaluated.

Effective Hamiltonian parameters for ab initio energy-level calculations of SrCl2:Yb2+ and CsCaBr3:Yb2+.

Calculated energy levels from recent ab initio studies of the electronic structure of SrCl2:Yb(2+) and CsCaBr3:Yb(2+) are fitted with a semi-empirical 'crystal-field' Hamiltonian, which acts within the model space 4f(14) + 4f(13)5d + 4f(13)6s. Parameters are obtained for the minima of the potential energy curves for each energy level and also for a range of anion-cation separations. The parameters are compared with published parameters fitted to experimental data and to atomic calculations. The states with significant 4f(13)6s character give a good approximation to the impurity-trapped exciton states that appear in the ab initio calculations.