Some unexamined aspects of analysis of covariance in pretest-posttest studies

The use of an analysis of covariance (ANCOVA) model in a pretest-posttest setting deserves to be studied separately from its use in other (non-pretest-posttest) settings. For pretest-posttest studies, the following points are made in this article: (a) If the familiar change from baseline model accurately describes the data-generating mechanism for a randomized study then it is impossible for unequal slopes to exist. Conversely, if unequal slopes exist, then it implies that the change from baseline model as a data-generating mechanism is inappropriate. An alternative data-generating model should be identified and the validity of the ANCOVA model should be demonstrated. (b) Under the usual assumptions of equal pretest and posttest within-subject error variances, the ratio of the standard error of a treatment contrast from a change from baseline analysis to that from ANCOVA is less than 2(1)/(2). (c) For an observational study it is possible for unequal slopes to exist even if the change from baseline model describes the data-generating mechanism. (d) Adjusting for the pretest variable in observational studies may actually introduce bias where none previously existed.     

Some aspects of the plant radioresistance

Mutant strains of unicellular green algae--Chlorella and Chlamydomonas which differ in their radioresistance have been investigated at different levels: cellular, molecular, biochemical and ultrastructural. It is obtained that several futures are typical for investigated strains. There are several features typical for radioresistant mutant strains investigated by us: in some cases a relationship was found between radioresistance and ssb-DNA repair efficiency; a high level of SH-groups; SOD; pigments content, especially carotenoids and chlorophyll a; a lower level of Pro content; a stability of the ultrastructural cell components or/and of the presence and structure of the cell envelope.     

Associations between the rates of maturation of the bones of the hand-wrist

Skeletal maturation rates for the age interval 3 to 13 years were analyzed using bone-specific assessments (Greulich-Pyle) of serial radiographs of 40 children. The mean rates of skeletal maturation resembled those of the population from which the atlas standards had been derived. There was a linear trend of skeletal age against chronological age for most bones in each sex. Regression lines were fitted to these data and the b values of the regression lines were calculated. Communality indices were calculated from an intercorrelation matrix of these b values. There was a statistically significant rank order correlation between the sexes in the communality indices. They tended to be higher in the girls than in the boys and were relatively low for the radius, ulna and carpals. Communality indices within groups of bones were high in all rows, especially the metacarpals, but in each sex they were comparatively low in the first ray (metacarpal plus the phalanges of the corresponding digit) and in the fifth ray of the boys. Neighborhood effects on the levels of association of maturation rates were present, particularly in the carpus, but marginal effects were not noted.     

Some aspects of the immunology of pseudotuberculosis

Integral evaluation of some humoral and cellular immunity factors in patients with pseudotuberculosis (Far-East scarlatinoid fever) with varying severity of its course was carried out. Inadequate immune reaction of human organism in response to infection with pseudotuberculosis was established at the level of both specific (sporadic cases of lacking synthesis or poor synthesis of IgM antibodies, lacking synthesis of IgG antibodies) and non-specific factors (incomplete phagocytic reaction). Phagocytosis is higher in monocytes than in neutrophils during pseudotuberculosis. The opsonizing properties of blood serum, the intensity of which increases in the course of disease, are great importance in freeing the organism from bacteria of pseudotuberculosis. The most rapid and technically simplest is the determination of antibodies in blood serum of the patients by means of the reaction of indirect hemagglutination. For this purpose the authors developed a new, highly sensitive, and specific preparation - the dry erythrocyte antigenic diagnostic agent.     

Some unsolved aspects of the parasitism problem

Various interpretations of the parasitism phenomenon exist. In this work data supporting the ecological understanding of its nature are presented. For parasitic species formed in the process of evolution the host organism has become the habitat (nutrition, multiplication), i.e., the environment, where interactions between the host and parasites are governed by ecological regularities. The consequences of this interactions are different (disease, asymptomatic infection), being secondary they reflect the result of concrete interactions. For this reason parasitism should not be identified in terms of only one consequence of such interaction--the development of pathologic processes.