145 research outputs found

    The Power Spectrum of Mass Fluctuations Measured from the Lyman-alpha Forest at Redshift z=2.5

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    We measure the linear power spectrum of mass density fluctuations at redshift z=2.5 from the \lya forest absorption in a sample of 19 QSO spectra, using the method introduced by Croft et al. (1998). The P(k) measurement covers the range 2\pi/k ~ 450-2350 km/s (2-12 comoving \hmpc for \Omega=1). We examine a number of possible sources of systematic error and find none that are significant on these scales. In particular, we show that spatial variations in the UV background caused by the discreteness of the source population should have negligible effect on our P(k) measurement. We obtain consistent results from the high and low redshift halves of the data set and from an entirely independent sample of nine QSO spectra with mean redshift z=2.1. A power law fit to our measured P(k) yields a logarithmic slope n=-2.25 +/- 0.18 and an amplitude \Delta^2(k_p) = 0.57^{+0.26}_{-0.18}, where Δ2\Delta^2 is the contribution to the density variance from a unit interval of lnk and k_p=0.008 (km/s)^{-1}. Direct comparison of our mass P(k) to the measured clustering of Lyman Break Galaxies shows that they are a highly biased population, with a bias factor b~2-5. The slope of the linear P(k), never previously measured on these scales, is close to that predicted by models based on inflation and Cold Dark Matter (CDM). The P(k) amplitude is consistent with some scale-invariant, COBE-normalized CDM models (e.g., an open model with \Omega_0=0.4) and inconsistent with others (e.g., \Omega=1). Even with limited dynamic range and substantial statistical uncertainty, a measurement of P(k) that has no unknown ``bias factors'' offers many opportunities for testing theories of structure formation and constraining cosmological parameters. (Shortened)Comment: Submitted to ApJ, 27 emulateapj pages w/ 19 postscript fig

    All metrics are equal, but some metrics are more equal than others: A systematic search and review on the use of the term ‘metric’

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    Objective: To examine the use of the term 'metric' in health and social sciences' literature, focusing on the interval scale implication of the term in Modern Test Theory (MTT). Materials and methods: A systematic search and review on MTT studies including 'metric' or 'interval scale' was performed in the health and social sciences literature. The search was restricted to 2001-2005 and 2011-2015. A Text Mining algorithm was employed to operationalize the eligibility criteria and to explore the uses of 'metric'. The paradigm of each included article (Rasch Measurement Theory (RMT), Item Response Theory (IRT) or both), as well as its type (Theoretical, Methodological, Teaching, Application, Miscellaneous) were determined. An inductive thematic analysis on the first three types was performed. Results: 70.6% of the 1337 included articles were allocated to RMT, and 68.4% were application papers. Among the number of uses of 'metric', it was predominantly a synonym of 'scale'; as adjective, it referred to measurement or quantification. Three incompatible themes 'only RMT/all MTT/no MTT models can provide interval measures' were identified, but 'interval scale' was considerably more mentioned in RMT than in IRT. Conclusion: 'Metric' is used in many different ways, and there is no consensus on which MTT metric has interval scale properties. Nevertheless, when using the term 'metric', the authors should specify the level of the metric being used (ordinal, ordered, interval, ratio), and justify why according to them the metric is at that level

    Creating a common metric based on existing activities of daily living tools to enable standardized reporting of functioning outcomes achieved during rehabilitation

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    Objective: Many different assessment tools are used to assess functioning in rehabilitation; this limits the comparability and aggregation of respective data. The aim of this study was to outline the development of an International Classification of Functioning, Disability and Health (ICF)-based interval-scaled common metric for 2 assessment tools assessing activities of daily living: the Functional Independence Measure (FIMTM) and the Extended Barthel Index (EBI), used in Swiss national rehabilitation quality reports. Methods: The conceptual equivalence of the 2 tools was assessed through their linking to the ICF. The Rasch measurement model was then applied to create a common metric including FIMTM and EBI. Subjects: Secondary analysis of a sample of 265 neurological patients from 5 Swiss clinics. Results: ICF linking found conceptual coherency of the tools. An interval-scaled common metric, including FIMTM and EBI, could be established, given fit to the Rasch model in the related analyses. Conclusion: The ICF-based and interval-scaled common metric enables comparison of patients� and clinics� functioning outcomes when different activities of daily living tools are used. The common metric can be included in a Standardized Assessment and Reporting System for functioning information in order to enable data aggregation and comparability

    The extended Barthel Index (EBI) can be reported as a unidimensional interval-scaled metric: a psychometric study

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    Background: The Extended Barthel Index (EBI), consisting of the original Barthel Index plus 6 cognitive items, provides a tool to monitor patients' outcomes in rehabilitation. Whether the EBI provides a unidimensional metric, thus can be reported as a valid sum-score, remains to be examined. Objective: To examine whether the EBI can be reported as unidimensional interval-scaled metric for neurological and musculoskeletal rehabilitation. Methods: Rasch analysis of a calibration sample of 800 cases from neurological or musculoskeletal rehabilitation in 2016 in Switzerland. Results: In the baseline analysis no fit to the Rasch Model was achieved. When accommodating local dependencies with a testlet approach satisfactory fit to the Rasch Model was achieved, and an interval scale transformation table was created. Conclusion: The results support the reporting of adapted EBI total scores for both rehabilitation groups by applying the interval scaled transformation table presented in this study.+ ID der Publikation: unilu_51329 + Sprache: Englisch + Letzte Aktualisierung: 2020-12-17 14:42:28 Abstract auf Englisch und Deutsc

    Scale‐Banking for Patient Reported Outcome Measures (PROMs) Measuring Functioning in Rheumatoid Arthritis: A Daily Activities Metric

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    Objective Functioning is an important outcome for rheumatoid arthritis (RA) management. Heterogeneity of respective patient‐reported outcome measures (PROMs) challenges direct comparisons between their results. This study aimed to standardize reporting of such PROMs measuring functioning in RA to facilitate comparability. Methods Common Item Non‐Equivalent Groups Design (NEAT) with the Health Assessment Questionnaire (HAQ) as a common scale across data sets from various countries (incl. UK, Turkey and Germany) to establish a common metric. Other PROMs included are the Physical Function items of the Multidimensional Health Assessment Questionnaire (MDHAQ), Disabilities of Arm, Shoulder and Hand (DASH), Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), World Health Organization Disability Assessment Schedule Version 2.0 (WHODAS 2.0), and four short forms (20, 10, 6, and 4 physical function items) from the Patient‐Reported Outcomes Measurement Information System (PROMIS). As the HAQ includes mobility, self‐care and domestic life items, this study focuses on these three domains. PROMs were described using Standard Error of Measurement (SEM) and Smallest Detectable Difference (SDD). Rasch Measurement model was used to create the common metric. Results Range of SEM is 0.2 (MDHAQ) to 7.4 (SF36‐PF). SDD revealed a range from 9.7 % (WOMAC‐RAT) to 33.5 % (WHODAS‐PF). PROMs co‐calibration revealed fit to the Rasch measurement model. A transformation table was developed to allow exchange between PROMs scores. Discussion Scores between the Daily Activity PROMs commonly used in RA can now be compared. Factors such as SEM and SDD help determine choice of PROM in clinical practice and research
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