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Biomedical subjects

L J Gross

Publications and source records attributed to L J Gross.

At least 19 recordsLinked to original sources
PubMed2000

Statistical report of the 1999 IBLCE examination.

This report summarizes the statistical analyses of the International Board of Lactation Consultant Examiners 1999 examination for certification as an International Board Certified Lactation Consultant. The summary includes information regarding exam translations and recertification rates.

Accreditation↗
PubMed1997

Validating standard setting with a modified nedelsky procedure through common item test equating.

It is often impossible to validate cut scores set using judged item review methods due to the fact that many high stakes testing programs attempt to limit the number of common items across consecutively administered forms. However, over time, with a stable item pool, secondary links through other test administrations allow the use of common item equating to test the stability of the judged cut scores. In this study five forms of a basic science examination administered over a three year period in a national board testing program were analyzed to determine the stability of judged cut scores. The stability was determined by comparison of the judged cut scores with the equated cut scores derived by the Rasch common item equating technique. The results indicate cut scores derived from the modified Nedelsky procedure were within equating error of the Rasch equated cut scores over five administrations.

Educational Measurement↗
PubMed1994

Cryo-electron microscopy of deoxy-sickle hemoglobin fibers.

Deoxy-sickle hemoglobin (HbS) polymerizes in vivo into long helical fibers which fill the red cell and make it rigid. This impedes red cell passage through the capillaries and is responsible for the clinical manifestations of sickle cell disease. Images of individual and laterally associated HbS fibers were obtained by electron microscopy of frozen hydrated specimens. Each fiber possesses variable pitch, having from 6 degrees to 12 degrees rotation per unit cell. Laterally associated HbS fibers display systematic inter-fiber contacts in spite of their pitch variations, and exhibit better order than isolated fibers. This suggest that inter-fiber contacts can act to couple fibers mechanically and might therefore be a factor in rigidifying red cells in vivo. Fiber variability was attributed to local torsional variations with a standard deviation of 2.5 degrees, but which are weakly coupled over a length of 2.25 unit cells. Variable pitch produces structural changes of as large as 5 A azimuthally and 6 A axially in HbS fiber unit cells.

Cryopreservation↗
PubMed1994

Variable pitch in frozen-hydrated sickle hemoglobin fibers: an image analysis model study.

The intracellular polymerization of deoxyhemoglobin S (HbS) into helical fibers is the primary pathological event which gives rise to sickle cell disease. The structure of these fibers has previously been studied by electron microscopy of negatively stained specimens. We are extending these studies with unstained frozen-hydrated HbS fibers (cryo-EM), which afford better visualization of the internal details of the fiber structure than can be achieved by negative staining, but have lower signal-to-noise ratio images. The pitch of the HbS fiber structure varies locally along any given particle. Because rotation about the particle axis thus is partially decoupled from translation along the axis, the pitch and angular rotation of a fiber unit cell cannot be inferred by symmetry (as is the case with constant pitch helices). Image analysis procedures are presented which are capable of explicitly identifying the pitch and angular rotation of individual HbS fiber unit cells having low signal-to-noise ratios. Fiber images are divided into segments one unit cell long (63 A) which are analyzed in two steps. First each unit cell is aligned with constant pitch electron density reference models by cross-correlation. Correlation coefficients are then used to determine angular rotation and pitch. This procedure was tested, and found to be robust, using model images corrupted to simulate experimental problems normally encountered in the analysis of cryo-electron micrographs. The effects of limited resolution, low signal-to-noise ratio, scaling errors, and rotational and axial misalignment are described.

Computer Simulation↗
PubMed1992

Scoring and setting pass/fail standards for an essay certification examination in nurse-midwifery.

Examination for certification or licensure of health professionals (credentialing) in the United States is almost exclusively of the multiple choice format. The certification examination for entry into the practice of the profession of nurse-midwifery has, however, used a modified essay format throughout its twenty-year history. The examination has recently undergone a revision in the method for score interpretation and for pass/fail decision-making. The revised method, described in this paper, has important implications for all health professional credentialing agencies which use modified essay, oral or practical methods of competency assessment. This paper describes criterion-referenced scoring, the process of constructing the essay items, the methods for assuring validity and reliability for the examination, and the manner of standard setting. In addition, two alternative methods for increasing the validity of the pass/fail decision are evaluated, and the rationale for decision-making about marginal candidates is described.

Certification↗
PubMed1990

Periodic solutions to nonautonomous difference equations.

A technique is presented for determining when periodic solutions to nonautonomous periodic difference equations exist. Under certain constraints, stable periodic solutions can be guaranteed to exist, and this is used to compare the analogous behavior of a nonautonomous periodic hyperbolic difference equation to that of the nonautonomous periodic Pearl-Verhulst logistic differential equation.

Mathematics↗
PubMed1989

Intermolecular contacts within sickle hemoglobin fibers.

By combining X-ray crystallographic co-ordinates of sickle hemoglobin (HbS) molecules with three-dimensional reconstructions of electron micrographs of HbS fibers we have synthesized a model for the structure of the clinically relevant HbS fiber. This model largely accounts for the action of 55 point mutations of HbS whose effect on fiber formation has been studied. In addition, it predicts locations at which additional point mutations are likely to affect fiber formation. The number of intermolecular axial contacts decreases with radius until, at the periphery of the fiber, there are essentially no axial contacts. We suggest that this observation accounts for the limited radial growth of the HbS fiber and that a similar mechanism may be a factor in limiting the size of other helical particles. The methodology for the synthesis of the fiber model is applicable to other systems in which X-ray crystallographic and electron microscopic data are available.

Crystallography↗
PubMed1989

Translating a health professional certification test to another language. A pilot analysis.

There has been increased pressure in recent years for examinations used for occupational and professional credentialing to be offered in several languages. When credentialing programs are international in scope, rather than national, examination translation may be a necessity, and a validation of the translation will be required. Yet, few candidates may sit for the translated version, jeopardizing the power and generalizability of statistical analysis. How should a board proceed in meeting its linguistic responsibility when faced with a small n? This article describes such a situation, and the linguistic and psychometric procedures that were developed and applied on a pilot translation by the International Board of Lactation Consultant Examiners (IBLCE).

Allied Health Personnel↗