Big GABA II: Water-referenced edited MR spectroscopy at 25 research sites

Accurate and reliable quantification of brain metabolites measured in vivo using 1H magnetic resonance spectroscopy (MRS) is a topic of continued interest. Aside from differences in the basic approach to quantification, the quantification of metabolite data acquired at different sites and on different platforms poses an additional methodological challenge. In this study, spectrally edited γ-aminobutyric acid (GABA) MRS data were analyzed and GABA levels were quantified relative to an internal tissue water reference. Data from 284 volunteers scanned across 25 research sites were collected using GABA+ (GABA + co-edited macromolecules (MM)) and MM-suppressed GABA editing. The unsuppressed water signal from the volume of interest was acquired for concentration referencing. Whole-brain T1-weighted structural images were acquired and segmented to determine gray matter, white matter and cerebrospinal fluid voxel tissue fractions. Water-referenced GABA measurements were fully corrected for tissue-dependent signal relaxation and water visibility effects. The cohort-wide coefficient of variation was 17% for the GABA + data and 29% for the MM-suppressed GABA data. The mean within-site coefficient of variation was 10% for the GABA + data and 19% for the MM-suppressed GABA data. Vendor differences contributed 53% to the total variance in the GABA + data, while the remaining variance was attributed to site- (11%) and participant-level (36%) effects. For the MM-suppressed data, 54% of the variance was attributed to site differences, while the remaining 46% was attributed to participant differences. Results from an exploratory analysis suggested that the vendor differences were related to the unsuppressed water signal acquisition. Discounting the observed vendor-specific effects, water-referenced GABA measurements exhibit similar levels of variance to creatine-referenced GABA measurements. It is concluded that quantification using internal tissue water referencing is a viable and reliable method for the quantification of in vivo GABA levels

A comparative study of secondary school examinations

SIGLEAvailable from British Library Document Supply Centre-DSC:7774.420(7) / BLDSC - British Library Document Supply CentreGBUnited Kingdo

When Change Matters: An Analysis of Survey Interaction in Dependent Interviewing on the British Household Panel Study

The authors examine how questionnaire structure affects survey interaction in the context of dependent interviewing (DI). DI is widely used in panel surveys to reduce observed spurious change in respondent circumstances. Although a growing literature generally finds beneficial measurement properties, little is known about how DI functions in interviews. The authors systematically observed survey interaction using behavior coding and analyzed an application of DI to obtain respondent employment characteristics. The authors found respondents indicated change in circumstances through a number of verbal machinations, including mismatch answers and explanations. Assessing whether these behaviors influenced subsequent question administration, the authors found qualitative evidence that the information disclosed when negating a DI question leads to subsequent interviewing errors. Quantitative analyses supported this evidence, suggesting that standardized interviewing deteriorates as respondents struggle to identify change in their circumstances. This analysis suggests that the reliability of detail about changed circumstances may not be improved using DI