Assessing validity in written tests of general practice - exploration by factor analysis of candidate response patterns to paper 1 of the MRCGP examination.

OBJECTIVE: To investigate the content validity of Paper 1 of the MRCGP examination. METHOD: Exploratory factor analysis was carried out on candidate responses to Paper 1 of the May and October MRCGP examination in 1998. Contribution of each test question across factors was assessed using a pattern matrix of the oblique rotation. Common dimensions and variations between factor sets were identified. Key testing areas were then matched against the 'domains of competence' intended to be assessed by Paper 1 (as defined within the examination blueprint matrix). RESULTS: Whilst critical appraisal, disease prevention/evidence-based medicine and clinical management emerged as areas tested consistently, content variation was observed between factor sets extracted from both sittings. In addition, some overlap, in terms of domains tested, was seen among other assessment instruments used within the examination. CONCLUSION: Paper 1 conforms to the majority of its stated intentions. However, further development of techniques for investigating validity will be required in order to minimize content variation between both sittings of the examination as well as to help more closely define areas of competence to be tested by Paper 1 of the MRCGP examination.

Expression of extraocular myosin heavy chain in rabbit laryngeal muscle.

The intrinsic laryngeal muscles of mammals are functionally heterogeneous, some of these muscles (e.g. the thyroarytenoid) contract extremely rapidly, like extraocular muscle, whilst others (e.g. the cricothyroid) contract as fast as limb fast muscle. The extraordinarily rapid contraction speed of extraocular muscles is associated with a fast myosin not found in limb muscles. In this work we explored the possibility that the thyroarytenoid muscle may also express this extraocular-specific fast myosin by raising a monoclonal antibody (mab 4A6) against its heavy chain. Electrophoretic separation of native isomyosins revealed that both the extraocular and the thyroarytenoid have two similar bands migrating ahead of bands found in limb fast or cricothyroid myosins. These two bands bound mab 4A6. The thyroarytenoid muscle can be divided into two divisions, a vocalis division which is important in phonation and an external division which functions in closing the glottis. Fibres in the vocalis are heterogeneous, some stain with mab 4A6, whilst others stain with mabs against limb myosin heavy chains. Fibres in the external division stain almost homogeneous with mab 4A6. The immunohistochemical staining pattern in the cricothyroid muscle resembled that of fast limb muscle: no fibres stained with mab 4A6. Thus, the high speed of contraction of the thyroarytenoid is associated with the same myosin heavy chain found in extraocular muscles, this characteristic is presumably an evolutionary adaptation for rapid closure of the glottis to enhance airway defense mechanisms.

The identification of a tissue-restricted plasma membrane marker in Xenopus laevis embryos by using a monoclonal antibody.

A library of monoclonal antibodies raised against partially purified membrane fractions from Xenopus laevis oocytes has been produced. One of these antibodies has been cloned and characterized in detail. It was found to be specific for a membrane-bound antigen of apparent Mr, 55,000. The distribution of the antigen has been studied by indirect immunofluorescence on sections of X. laevis embryos and has been found to be highly specific for some ectodermal and endodermal tissues. It was not present on mesodermal tissues.