Identifiability, exchangeability and confounding revisited

In 1986 the International Journal of Epidemiology published "Identifiability, Exchangeability and Epidemiological Confounding". We review the article from the perspective of a quarter century after it was first drafted and relate it to subsequent developments on confounding, ignorability, and collapsibility.     

Nucleoside peptides. 10. Synthesis and T-cell immunostimulatory properties of certain peptide derivatives of 6-azacadeguomycin

Several amino acid and peptide conjugates of 6-azacadeguomycin (6-amino-1-beta-D-ribofuranosyl-4,5-dihydro-4-oxopyrazolo[3,4-d]py rimidine- 3-carboxylic acid, 2) have been prepared in good yields, via a two-step procedure involving 1-hydroxybenzotriazole and 1-ethyl-3-[3-(dimethylamino)propyl]carbodiimide hydrochloride mediated coupling of 2 with an appropriately protected amino acid or peptide, followed by ammonolysis. Thus, condensation of 2 with L-phenylalanine methyl ester, glycine ethyl ester, and L-glutamic acid diethyl ester gave the corresponding protected linear nucleoside peptides (3, 5 and 7, respectively). Subsequent ammonolysis of 3, 5 and 7 furnished L-phenylalanine amide (4), glycine amide (6) and L-glutamic acid diamide (8) conjugates of 6-azacadeguomycin, respectively. Saponification of 7 gave the corresponding L-glutamic acid derivative 9. A similar coupling of 2 with L-phenylalaninyl-N epsilon-nitro-L-arginine methyl ester trifluoroacetate and subsequent ammonolysis (after catalytic hydrogenation) gave L-phenylalaninyl-L-arginine amide conjugate (12) of 6-azacadeguomycin. Compounds 2, 4, 6, 8, 9, and 12 were evaluated for their ability to potentiate T-cell responses to plant mitogens, in comparison with cadeguomycin (1). Compounds 4, 6, and 9 exhibited an increase in the T-cell proliferation in a dose-dependent manner.     

Post-traumatic stress disorder in the general population. Findings of the epidemiologic catchment area survey

There have been numerous studies of post-traumatic stress disorder in trauma victims, war veterans, and residents of communities exposed to disaster. Epidemiologic studies of this syndrome in the general population are rare but add an important perspective to our understanding of it. We report findings on the epidemiology of post-traumatic stress disorder in 2493 participants examined as part of a nationwide general-population survey of psychiatric disorders. The prevalence of a history of post-traumatic stress disorder was 1 percent in the total population, about 3.5 percent in civilians exposed to physical attack and in Vietnam veterans who were not wounded, and 20 percent in veterans wounded in Vietnam. Post-traumatic stress disorder was associated with a variety of other adult psychiatric disorders. Behavioral problems before the age of 15 predicted adult exposure to physical attack and (among Vietnam veterans) to combat, as well as the development of post-traumatic stress disorder among those so exposed. Although some symptoms of post-traumatic stress disorder, such as hyperalertness and sleep disturbances, occurred commonly in the general population, the full syndrome as defined by the Diagnostic and Statistical Manual of Mental Disorders, third edition, was common only among veterans wounded in Vietnam.     

Difficult-to-recruit respondents and their effect on prevalence estimates in an epidemiologic survey

Generous contact efforts were used to recruit 3,004 respondents into the first wave of the St. Louis Epidemiologic Catchment Area (ECA) project, a psychiatric epidemiologic study of the general population, conducted from 1981-1982. These efforts were analyzed to establish which sociodemographic characteristics or current psychiatric disorders were determinants of difficulty in recruitment. Being young, male, black, a nonrural resident, educated, and full-time employed were the demographic characteristics associated with increased contact efforts. Persons currently meeting criteria for an alcohol disorder required almost 20% more contact attempts than those without the disorder; this difficulty lay both in their being less available for an initial contact and refusing at a higher rate once contacted. An optimal recruitment effort cutoff point is provided, and a method is suggested for detecting that optimal point in the course of ongoing studies.     

Sample size considerations when groups are the appropriate unit of analysis.

This article discusses issues to be considered by nurse researchers when groups should be used as the unit of randomization. Advantages and disadvantages are presented, with statistical calculations needed to determine the effective sample size. Examples of these concepts are presented using data from the Black Cosmetologists Promoting Health Program. Different hypothetical scenarios and their impact on sample size are also presented. Given the complexity of calculating the sample size when using groups as the unit of randomization, it is advantageous for researchers to work closely with statisticians when designing and implementing studies that anticipate the use of groups as the unit of randomization.     

Solution of the discrete Plateau problem

We solve a discrete version of the classic Plateau problem, which asks for a minimal surface spanning a given curve. Our algorithm is based on a network-flow formulation that finds minimal slabs, intuitively corresponding to minimal "surfaces" of prescribed thickness. We let the slab thickness approach zero in order to obtain the desired minimal surface.     

Relative carriage rates of nuclear dehydrogenating clostridia in two populations of different colorectal cancer risk

Carriage of nuclear dehydrogenating clostridia has been associated with colon cancer and implicated in its aetiology. This study has compared the carriage of these organisms in a British population at high risk for the development of colon cancer with a low risk Nigerian population. Clostridia were found in all of the stools from both populations. Nuclear dehydrogenating clostridia were only found in the stools of the British subjects (32%). These results support the suggestion that the carriage rate of nuclear dehydrogenating clostridia in a population is related to the risk of colon cancer.     

In vitro activation of natural killer-like cytotoxicity by specifically in vivo primed T-helper lymphocytes in the rat.

The interaction between the rat non-cytotoxic T lymphocyte subset, which is marked by the W3/25 monoclonal antibody, and natural killer cells was investigated. Specifically in vivo primed lymph node cells were restimulated in vitro with the priming antigen and co-cultured with a source of natural killer cells and their precursors. Cytotoxic activity, generated during a 4 day incubation period, was assessed by lysis of a rat natural killer cell-sensitive tumour target cell line, y3Ag123. This cytotoxic activity was more fully described as natural killer cell cytotoxicity on the basis of target cell specificity, using a range of natural killer cell-susceptible and -resistant targets. The W3/25-positive T cell, separated from the in vivo primed lymph node cells by nylon wool column elution, antibody labelling and sorting on the fluorescence-activated cell sorter, was shown to be necessary to stimulate the generation of this activity. W3/25-negative cells were not active in this respect. The activation was shown to be mediated via lymphokine(s), probably interleukin-2, present in concanavalin A-induced lymphocyte culture supernatants. These supernatants could be used to substitute for in vivo primed, restimulated W3/25-positive lymph node cells in activating natural killer cell cytotoxicity from normal spleen cells. Nylon wool column-eluted spleen cells, activated in vitro with conditioned medium were separated into OX8-positive and OX8-negative subsets using the fluorescence-activated cell sorter. The distribution of cytotoxic activity related to that of freshly derived rat natural killer cells.     

Development of hatching blastocysts from immature human oocytes following in-vitro maturation and fertilization using a co-culture system

Recently, in-vitro maturation (IVM) of immature human oocytes recovered from non-stimulated follicles has been applied in the treatment of infertility. However, in previous reports, very few embryos cultured in conventional medium have reached the expanded blastocyst stage following in-vitro maturation and fertilization (IVM/IVF). The objective of this study was to investigate whether the developmental competence of human embryos following IVM/IVF could be enhanced by the use of a human ampullary cell co-culture system. Immature human oocytes were aspirated from small follicles at Caesarean section and then cultured in medium containing human menopausal gonadotrophin for 36 to 48 h, followed by insemination. Zygotes were randomly cultured either in conventional culture medium alone or in the co-culture system. Of 48 embryos cultured in conventional medium alone, all arrested at the 2-16- cell stage on day 3 after insemination. Of 46 embryos cultured in the co-culture system, 26 embryos (56.5%) arrested at the 2-16-cell stage. Six embryos (13%) developed to the morula stage. Fourteen embryos (30.4%) developed to expanded blastocysts and two blastocysts were hatching on day 7 after insemination. We conclude that co-culture significantly enhances the development of blastocysts in embryos resulting from IVM/IVF.