Conducting Web-Based Surveys

Web-based surveying is becoming widely used in social science and educational research. The Web offers significant advantages over more traditional survey techniques however there are still serious methodological challenges with using this approach. Currently coverage bias or the fact significant numbers of people do not have access, or choose not to use the Internet is of most concern to researchers. Survey researchers also have much to learn concerning the most effective ways to conduct surveys over the Internet. While in its early stages, research on Internet-based survey methodology has identified a number of factors that influence data quality. Of note, several studies have found Internet surveys have significantly lower response rates than comparable mailed surveys. Several factors have been found to increase response rates including personalized email cover letters, follow-up reminders, pre-notification of the intent to survey and simpler formats. A variety of software tools are now available for conducting Internet surveys and they are becoming a increasing sophisticated and easy to use. While there is a need for caution, the use of Web-based surveying is clearly going to grow

A Randomized Trial Comparing Digital and Live Lecture Formats

Problem Statement and Background – Medical education is increasingly being conducted in community-based teaching sites making it difficult to provide a consistent curriculum. We conducted a randomized trial to assess whether digital lectures could replace live lectures. Methods – Students were randomized to either attending a lecture series at our main campus or viewing digital versions of the same lectures at community sites. Both groups completed an examination based on the lectures and the group viewing the digital lectures completed a feedback form. Results – The group who viewed the digital lectures performed slightly better than the live lecture group however the differences were not statistically significant. Despite technical problems the students who viewed the digital lectures overwhelmingly felt the digital lectures could replace live lectures. Conclusions – Digital lectures appear to be a viable alternative to live lectures as a means of delivering didactic presentations in a community-based setting

Models for discriminating image blur from loss of contrast

Observers can discriminate between blurry and low-contrast images (Morgan, 2017). Wang and Simoncelli (2004) demonstrated that a code for blur is inherent to the phase relationships between localized pattern detectors of different scale. To test whether human observers actually use local phase coherence when discriminating between image blur and loss of contrast, we compared phase-scrambled chessboards with unscrambled chessboards. Although both stimuli had identical amplitude spectra, local phase coherence was disrupted by phase-scrambling. Human observers were required to concurrently detect and identify (as contrast or blur) image manipulations in the 2x2 forced-choice paradigm (Nachmias & Weber, 1975; Watson & Robson, 1981) traditionally considered to be a litmus test for "labelled lines" (i.e. detection mechanisms that can be distinguished on the basis of their preferred stimuli). Phase scrambling reduced some observers’ ability to discriminate between blur and a reduction in contrast. However, none of our observers produced data consistent with Watson & Robson’s most stringent test for labelled lines, regardless whether phases were scrambled or not. Models of performance fit significantly better when either a) the blur detector also responded to contrast modulations, b) the contrast detector also responded to blur modulations, or c) noise in the two detectors was anticorrelate

A visual search asymmetry for novelty in the visual field based on sensory adaptation

The ability to detect sudden changes in the environment is important for survival. However, studies of “change blindness” have shown that image differences are hard to detect when a time delay or a mask is imposed between the different images. However, when sensory adaptation is permitted by accuratefixation, we find that change detection is not only possible but asymmetrical: a single changed target amongst 15 unchanging distractors is much easier to detect than a target defined by its lack of change. Although adaptation may selectively reduce the apparent contrast of unchanged objects, the asymmetry in “change salience” cannot be attributed to any such reduction because genuine reductions in target contrast increase, rather than decrease, target detectability. Analogous results preclude attribution to apparent differences between a) target onset and distractor onset and b) their temporal frequencies (both flickered at 7.5 Hz, minimizing afterimages). Our results demonstrate a hitherto underappreciated (or unappreciated) advantage conferred by low-level sensory adaptation: it automatically elevates the salience of previously absent objects

Quadratic maps with a periodic critical point of period 2

We provide a complete classification of possible graphs of rational preperiodic points of endomorphisms of the projective line of degree 2 defined over the rationals with a rational periodic critical point of period 2, under the assumption that these maps have no periodic points of period at least 7. We explain how this extends results of Poonen on quadratic polynomials. We show that there are 13 possible graphs, and that such maps have at most 9 rational preperiodic points. We provide data related to the analogous classification of graphs of endomorphisms of degree 2 with a rational periodic critical point of period 3 or 4.Comment: Updated theorem 2 to rule out the cases of quadratic maps with a rational periodic critical point of period 2 and a rational periodic point of period 5 or

Sources of Measurement Error in an ECG Examination: Implications for Performance-Based Assessments

Objective: To assess the sources of measurement error in an electrocardiogram (ECG) interpretation examination given in a third-year internal medicine clerkship. Design: Three successive generalizability studies were conducted. 1) Multiple faculty rated student responses to a previously administered exam. 2) The rating criteria were revised and study 1 was repeated. 3) The examination was converted into an extended matching format including multiple cases with the same underlying cardiac problem. Results: The discrepancies among raters (main effects and interactions) were dwarfed by the error associated with case specificity. The largest source of the differences among raters was in rating student errors of commission rather than student errors of omission. Revisions in the rating criteria may have helped increase inter-rater reliability slightly however, due to case specificity, it had little impact on the overall reliability of the exam. The third study indicated the majority of the variability in student performance across cases was in performance across cases within the same type of cardiac problem rather than between different types of cardiac problems. Conclusions: Case specificity was the overwhelming source of measurement error. The variation among cases came mainly from discrepancies in performance between examples of the same cardiac problem rather than from differences in performance across different types of cardiac problems. This suggests it is necessary to include a large number of cases even if the goal is to assess performance on only a few types of cardiac problems

Experience, expertise and expert-performance research in public accounting

Bibliography: p. [22-25]