Cross-national health comparisons using the Rasch model: findings from the 2012 US Health and Retirement Study and the 2012 Mexican Health and Aging Study

Purpose Cross-national comparisons of patterns of population aging have emerged as comparable national micro-data have become available. This study creates a metric using Rasch analysis and determines the health of American and Mexican older adult populations. Methods Secondary data analysis using representative samples aged 50 and older from 2012 U.S. Health and Retirement Study (n&thinsp;=&thinsp;20,554); 2012 Mexican Health and Aging Study (n&thinsp;=&thinsp;14,448). We developed a function measurement scale using Rasch analysis of 22 daily tasks and physical function questions. We tested psychometrics of the scale including factor analysis, fit statistics, internal consistency, and item difficulty. We investigated differences in function using multiple linear regression controlling for demographics. Lastly, we conducted subgroup analyses for chronic conditions. Results The created common metric demonstrated a unidimensional structure with good item fit, an acceptable precision (person reliability&thinsp;=&thinsp;0.78), and an item difficulty hierarchy. The American adults appeared less functional than adults in Mexico (&beta;&nbsp;=&thinsp;&minus;&thinsp;0.26, p&thinsp;&lt;&thinsp;0.0001) and across two chronic conditions (arthritis, &beta;&nbsp;=&thinsp;&minus;&thinsp;0.36; lung problems, &beta;&nbsp;=&thinsp;&minus;&thinsp;0.62; all p&thinsp;&lt;&thinsp;0.05). However, American adults with stroke were more functional than Mexican adults (&beta;&nbsp;=&thinsp;0.46, p&thinsp;=&thinsp;0.047). Conclusions The Rasch model indicates that Mexican adults were more functional than Americans at the population level and across two chronic conditions (arthritis and lung problems). Future studies would need to elucidate other factors affecting the function differences between the two countries.</p

Specialized proteomic responses and an ancient photoprotection mechanism sustain marine green algal growth during phosphate limitation

Marine algae perform approximately half of global carbon fixation, but their growth is often limited by the availability of phosphate or other nutrients 1,2 . As oceans warm, the area of phosphate-limited surface waters is predicted to increase, resulting in ocean desertification 3,4 . Understanding the responses of key eukaryotic phytoplankton to nutrient limitation is therefore critical 5,6 . We used advanced photo-bioreactors to investigate how the widespread marine green alga Micromonas commoda grows under transitions from replete nutrients to chronic phosphate limitation and subsequent relief, analysing photosystem changes and broad cellular responses using proteomics, transcriptomics and biophysical measurements. We find that physiological and protein expression responses previously attributed to stress are critical to supporting stable exponential growth when phosphate is limiting. Unexpectedly, the abundance of most proteins involved in light harvesting does not change, but an ancient light-harvesting-related protein, LHCSR, is induced and dissipates damaging excess absorbed light as heat throughout phosphate limitation. Concurrently, a suite of uncharacterized proteins with narrow phylogenetic distributions increase multifold. Notably, of the proteins that exhibit significant changes, 70 are not differentially expressed at the mRNA transcript level, highlighting the importance of post-transcriptional processes in microbial eukaryotes. Nevertheless, transcript-protein pairs with concordant changes were identified that will enable more robust interpretation of eukaryotic phytoplankton responses in the field from metatranscriptomic studies. Our results show that P-limited Micromonas responds quickly to a fresh pulse of phosphate by rapidly increasing replication, and that the protein network associated with this ability is composed of both conserved and phylogenetically recent proteome systems that promote dynamic phosphate homeostasis. That an ancient mechanism for mitigating light stress is central to sustaining growth during extended phosphate limitation highlights the possibility of interactive effects arising from combined stressors under ocean change, which could reduce the efficacy of algal strategies for optimizing marine photosynthesis. © 2018 The Author(s)