Discrimination and reliability: equal partners? Understanding the role of discriminative instruments in HRQoL research: can Ferguson's Delta help? A response

A response to Norman GR 'Discrimination and reliability: equal partners?' and Wyrwich KW 'Understanding the role of discriminative instruments in HRQoL research: can Ferguson's Delta help?

Questionnaire discrimination: (re)-introducing coefficient δ

Background: Questionnaires are used routinely in clinical research to measure health status and quality of life. Questionnaire measurements are traditionally formally assessed by indices of reliability (the degree of measurement error) and validity (the extent to which the questionnaire measures what it is supposed to measure). Neither of these indices assesses the degree to which the questionnaire is able to discriminate between individuals, an important aspect of measurement. This paper introduces and extends an existing index of a questionnaire's ability to distinguish between individuals, that is, the questionnaire's discrimination. Methods: Ferguson (1949) [1] derived an index of test discrimination, coefficient δ, for psychometric tests with dichotomous (correct/incorrect) items. In this paper a general form of the formula, δ G , is derived for the more general class of questionnaires allowing for several response choices. The calculation and characteristics of δ G are then demonstrated using questionnaire data (GHQ-12) from 2003–2004 British Household Panel Survey (N = 14761). Coefficients for reliability (α) and discrimination (δ G ) are computed for two commonly-used GHQ-12 coding methods: dichotomous coding and four-point Likert-type coding. Results: Both scoring methods were reliable (α > 0.88). However, δ G was substantially lower (0.73) for the dichotomous coding of the GHQ-12 than for the Likert-type method (δ G = 0.96), indicating that the dichotomous coding, although reliable, failed to discriminate between individuals. Conclusion: Coefficient δ G was shown to have decisive utility in distinguishing between the cross-sectional discrimination of two equally reliable scoring methods. Ferguson's δ has been neglected in discussions of questionnaire design and performance, perhaps because it has not been implemented in software and was restricted to questionnaires with dichotomous items, which are rare in health care research. It is suggested that the more general formula introduced here is reported as δ G , to avoid the implication that items are dichotomously coded

Validity of two common asthma-specific quality of life questionnaires: Juniper mini asthma quality of life questionnaire and Sydney asthma quality of life questionnaire

Background This study explored the psychometric properties (internal consistency, construct validity, discriminative ability) of the Juniper Mini Asthma Quality of Life Questionnaire (Mini AQLQ-J) and the Sydney Asthma Quality of Life Questionnaire (AQLQ-S). Methods One hundred fourty-six adults (18-45 years) with asthma requiring regular inhaled corticosteroids were recruited to a trial of written emotional disclosure. Correlational analyses were performed to understand the relationship of the two measures with each other, with symptoms, lung function, asthma control, asthma bother and generic quality of life. Median quality of life scores were compared according to gender, health care usage and levels of asthma severity. Results AQLQ-J and AQLQ-S total scores correlated strongly with each other (rho = -0.80) and moderately with the EuroQol Current Health Status Scale (AQLQ-J: rho = 0.35; AQLQ-S: rho = -0.40). Domain score correlations between AQLQ-J and AQLQ-S were mostly moderate (0.5 < rho < 0.8). Both QoL measures were significantly correlated with symptom score. Correlations with the symptom score asthma module (AQLQ-J: rho = -0.69; AQLQ-S: rho = 0.50) were stronger compared with the total symptom score and the symptom score rhinitis module (AQLQ-J: rho = -0.41; AQLQ-M: rho =0.31). Neither QoL measure was significantly correlated with FEV1 % predicted at the total or the domain level. Total scores of both measures were significantly correlated with subjective asthma control (AQLQ-J: rho = 0.68; AQLQ-S: rho = -0.61) and asthma bother (AQLQ-J: rho = -0.73; AQLQ-M: rho = 0.73). Conclusions This study provides further evidence for the validity of the AQLQ-J and the AQLQ-S in a British population of adult patients with asthma managed in primary care. Correlations with lung function parameters were weak or absent. Correlations with generic quality of life were moderate, those with asthma symptoms, asthma control and asthma bother were strong. Both measures are able to discriminate between levels of asthma severity

An Infrared Study of the Circumstellar Material Associated with the Carbon Star R Sculptoris

The asymptotic giant branch (AGB) star R Sculptoris (R Scl) is one of the most extensively studied stars on the AGB. R Scl is a carbon star with a massive circumstellar shell ($M_{shell}\sim 7.3\times10^{-3}~M_{\odot}$) which is thought to have been produced during a thermal pulse event $\sim2200$ years ago. To study the thermal dust emission associated with its circumstellar material, observations were taken with the Faint Object InfraRed CAMera for the SOFIA Telescope (FORCAST) at 19.7, 25.2, 31.5, 34.8, and 37.1 $\mu$m. Maps of the infrared emission at these wavelengths were used to study the morphology and temperature structure of the spatially extended dust emission. Using the radiative transfer code DUSTY and fitting the spatial profile of the emission, we find that a geometrically thin dust shell cannot reproduce the observed spatially resolved emission. Instead, a second dust component in addition to the shell is needed to reproduce the observed emission. This component, which lies interior to the dust shell, traces the circumstellar envelope of R Scl. It is best fit by a density profile with $n \propto r^{\alpha}$ where $\alpha=0.75^{+0.45}_{-0.25}$ and dust mass of $M_d=9.0^{+2.3}_{-4.1}\times10^{-6}~M_{\odot}$. The strong departure from an $r^{-2}$ law indicates that the mass-loss rate of R Scl has not been constant. This result is consistent with a slow decline in the post-pulse mass-loss which has been inferred from observations of the molecular gas.Comment: 10 pages, 10 figures, accepted to Ap

Early drug use of dapagliflozin prescribed by general practitioners and diabetologists in Germany.

OBJECTIVES: Dapagliflozin is an inhibitor of the human sodium-glucose co-transporter 2 (SGLT2) that has been shown to improve glycaemic control in patients with type 2 diabetes mellitus (T2DM). This study aimed to evaluate the characteristics and treatment patterns of dapagliflozin users in comparison to users of other anti-diabetic (AD) treatments in Germany. METHODS: Data from patients with T2DM initiating at least one prescription for dapagliflozin or other AD therapy between November 2012 and April 2014 were collected from the IMS German Disease Analyzer database. RESULTS: The use of dapagliflozin combination therapy (n=1034; 74%) was more common than monotherapy (n=371; 26%). In comparison with other AD therapy users, a higher percentage of dapagliflozin users were ⩽64years of age (62.3% vs. 36.4%), and a higher proportion were male (59.1% vs. 53.6%). The average duration of diabetes was comparable between dapagliflozin patients and other AD therapy users (5.7yearsvs. 5.5years), however higher levels of HbA1c were found in dapagliflozin users (8.2% (66mmol/mol) vs. 7.5% (58mmol/mol). For the vast majority (71.5% of 10mg dapagliflozin users and 88.9% of 5mg users), dapagliflozin was prescribed in combination with other AD therapy. CONCLUSIONS: Patients starting on dapagliflozin differed in several demographic and health-related respects to patients starting another AD therapy during the same period. Dapagliflozin was predominantly used as a component of combination therapy, adding on to existing therapy. After initiation, switching to other AD treatments or adding to therapy was comparatively rare during the first year

High time-resolution observations of the Vela pulsar

We present high time resolution observations of single pulses from the Vela pulsar (PSR B0833-45) made with a baseband recording system at observing frequencies of 660 and 1413 MHz. We have discovered two startling features in the 1413 MHz single pulse data. The first is the presence of giant micro-pulses which are confined to the leading edge of the pulse profile. One of these pulses has a peak flux density in excess of 2500 Jy, more than 40 times the integrated pulse peak. The second new result is the presence of a large amplitude gaussian component on the trailing edge of the pulse profile. This component can exceed the main pulse in intensity but is switched on only relatively rarely. Fluctutation spectra reveal a possible periodicity in this feature of 140 pulse periods. Unlike the rest of the profile, this component has low net polarization and emits predominantly in the orthogonal mode. This feature appears to be unique to the Vela pulsar. We have also detected microstructure in the Vela pulsar for the first time. These same features are present in the 660 MHz data. We suggest that the full width of the Vela pulse profile might be as large as 10 ms but that the conal edges emit only rarely.Comment: 6 pages, 5 figures, In Press with ApJ Letter

Healthcare for truck drivers: Assessing accessibility and appropriateness of South African Roadside Wellness Centres

Background Truck drivers occupy a pivotal role in the economies of southern Africa, due to limited rail, water and other forms of transport of goods. The occupational nature of truck driving limits access to healthcare. North Star Alliance (North Star) offers a tailored primary healthcare service for truck drivers along the sub-Saharan trucking corridor. Objectives The overall objective of this study was to explore truck drivers’ views regarding access to, and appropriateness of, selected South African North Star Roadside Wellness Centres (RWCs) coupled with understanding their health-seeking behaviour. Methods We conducted semi-structured interviews with two groups of purposively-sampled truck drivers: 24 who accessed North Star RWCs and 22 who knew about the centres but did not use them. The interviews explored access, health-seeking behaviour, and healthcare experiences. Additional information on risk perceptions emerged. Qualitative data were organised into four themes: client satisfaction, health-seeking behaviour, risk perception and behaviour, and service delivery strengthening. Results The majority of those interviewed were older (36–65 years old), South African, with secondary education, employed full-time, in stable relationships, and having children. Overall users were satisfied with RWC locations, operating hours, infrastructure, and healthcare worker attitudes. Half of the non-users did not access routine healthcare anywhere. Non-users primarily did not access the RWCs because they did not know the operating times and preferred local facilities. Both groups used traditional healers and pharmacies. RWC users accessed traditional healers and pharmacies for services not available to them at the RWCs. Both groups reported not using private general practitioners or specialists. Both groups provided recommendations for strengthening the service delivery model including an increased focus on non-communicable diseases and occupationally-required health services including vaccinations. Conclusion Comprehensive care packages delivered through accessible satellite facilities should form the foundation of service delivery models for truck drivers and other mobile populations

Psychological impact of human papillomavirus testing in women with borderline or mildly dyskaryotic cervical smear test results: cross sectional questionnaire study.

OBJECTIVE: To describe the psychological impact on women of being tested for human papillomavirus (HPV) when smear test results are borderline or mildly dyskaryotic. DESIGN: Cross sectional questionnaire study. SETTING: Two centres participating in an English pilot study of HPV testing in women with borderline or mildly dyskaryotic smear test results. PARTICIPANTS: Women receiving borderline or mildly dyskaryotic smear test results tested for HPV and found to be HPV positive (n = 536) or HPV negative (n = 331); and women not tested for HPV with borderline or mildly dyskaryotic smear results (n = 143) or normal smear results (n = 366). MAIN OUTCOME MEASURES: State anxiety, distress, and concern about test result, assessed within four weeks of receipt of results. RESULTS: Women with borderline or mildly dyskaryotic smear results who were HPV positive were more anxious, distressed, and concerned than the other three groups. Three variables independently predicted anxiety in HPV positive women: younger age (beta = -0.11, P = 0.03), higher perceived risk of cervical cancer (beta = 0.17, P < 0.001), and reporting that they did not understand the meaning of test results (beta = 0.17, P = 0.001). Testing HPV negative was not reassuring: among women with abnormal smear test results, those who were HPV negative were no less anxious than those who were not tested for HPV. CONCLUSIONS: Informing women more effectively about the meaning of borderline or mildly dyskaryotic smear test results and HPV status, in particular about the absolute risks of cervical cancer and the prevalence of HPV infection, may avoid some anxiety for those who are HPV positive while achieving some reassurance for those who test HPV negative