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PubMed1991

Theory-based screening for prevention: focusing on mediating processes in children of divorce.

Prevention programs in mental health theoretically can benefit from selecting participants who have a greater likelihood of developing psychological problems because of their exposure to the putative mediators targeted for change in an intervention. Screening on mediators may increase statistical power to detect program effects, enhance the cost-effectiveness of intervention trials, and decrease the possibility of iatrogenic effects. The circumstances that optimize the strategy of screening on the basis of mediating variables are discussed, and data are presented to illustrate the development of a mediational selection strategy to identify families who might best benefit from a preventive intervention for children of divorce. In addition, we present evidence that adjustment problems for children experiencing a divorce, as with most mental health problems, are not the result of one specific factor, but are jointly determined by several mediating processes that occur subsequent to the divorce. The mediational selection strategy developed illustrates the utility of measuring a set of mediational processes central to conferring risk for mental health problems to children of divorce.

Adolescent↗
PubMed1991

Mediational screening: is the benefit worth the cost?

Argued that Pillow et al. (1991) may have overestimated the benefits of mediational screening and underestimated the costs involved in the procedure. The three benefits they suggest: increased statistical power to detect prevention effects, increased cost-effectiveness, and decreased iatrogenic effects are shown to be modest at best. Costs associated with misclassifying people as either false positives or false negatives are considered in the total cost/benefit analysis of mediational screening. Because we cannot accurately predict who will react to the occurrence of life stress by developing the conditions we are interested in preventing, universal interventions are advocated.

Adaptation, Psychological↗
PubMed1991

Mediational screening as a model for prevention research.

Examined here is Pillow, Sandler, Braver, Wolchik, and Gersten's (this issue) strategy for screening prevention trial participants. The reviewer concludes that their selection strategy should increase the statistical power of prevention outcome studies, increase intervention cost effectiveness, and help to prevent their possible iatrogenic effects. Also, their model points up inadequacies in the longitudinal data on which most prevention strategies are based, and their model could well serve as a template for future research.

Child↗
PubMed1991

A random allocation system with the minimization method for multi-institutional clinical trials.

This paper describes the random allocation system used to perform precise and rapid treatment assignments in multi-institutional clinical trials. This system is based on sophisticated randomization procedures, according to Pocock and Simon's minimization method and Zelen's method for institution balancing. The major advantage of randomized treatment assignments with this system is to balance treatment numbers for each level of various prognostic factors over the entire trial and at the same time balance the allocation of treatments within an institution. Therefore, the randomized treatment assignments by this system can prevent degrading of the statistical power of a particular treatment factor. This system is designed to run on a small-sized notebook computer and therefore can be set up beside a telephone for registration, without occupying a large space. At present, this system is conveniently being used in two clinical trials.

Algorithms↗
PubMed1988

The assessment of bioavailability in the presence of nonlinear elimination.

The simultaneous administration of an oral dose and intravenous tracer dose, as a method to determine bioavailability, was examined by means of computer simulation for drugs exhibiting Michaelis-Menten type elimination. A physiological pharmacokinetic model parameterized for man and including first-order absorption and elimination solely from the liver was employed. This tracer method provided good estimates of the true availability, with an error of 6% or less, over a wide range of dosing and dispositional conditions. Poorer estimates were noted when large doses of drugs with very short half-lives were considered. This poor performance was improved by administering the intravenous tracer at some time after the oral dose but an a priori basis for establishing this time was not apparent. The tracer method, therefore, appears to be a robust means of assessing, in man, oral bioavailability in the presence of Michaelis-Menten type elimination for drugs characterized by the general properties of the physiological model employed and with half-lives in excess of approximately 40 min. These findings together with the statistical power and simplicity of performance of the tracer method indicate that it is a valid technique for the assessment of bioavailability under a wide range of kinetic conditions.

Biological Availability↗
PubMed1993

Quality assurance for bone densitometry research studies: concept and impact.

A concept for quality assurance (QA) in bone densitometry has been developed for clinical multicenter studies. Major elements provided by a coordinating center comprise (1) consulting services and certification of participating centers in the start-up phase of the study, (2) review of scan data acquired on QA standards for cross-calibration and longitudinal assessment of scanner stability, (3) review of selected patient data as well as of problem cases during the study, and (4) comprehensive review and correction of patient results based on QA data after conclusion of the study. Limitations of phantom-based QA data should be acknowledged. Typical problems encountered during research studies and guidelines for solutions are presented. Successful implementation of QA measures may yield substantial enhancement of statistical power. Depending on the study design and the variability of response within patient groups, improvement in precision due to QA measures may reduce the smallest detectable difference between subject groups or, alternatively, sample size by a few to more than 50%, and thus may contribute to a substantial reduction in study cost. Formulae for calculation of the magnitude of these effects are presented. To maximize the net benefit, QA efforts have to be limited to levels that assure reliability of the data at acceptable QA cost. While QA programs at individual clinical sites or for local practitioners may not need to be as extensive as for multicenter clinical trials, awareness of the potential problems and implementation of basic QA measures will help in obtaining high-quality bone densitometry results.

Bone Density↗
PubMedDate not supplied

Unilateral neck exploration for primary hyperparathyroidism: analysis of a controversy using a mathematical model.

Most endocrine surgeons explore both sides of the neck and identify all parathyroid glands when operating on patients with primary hyperparathyroidism. Others, however, advocate the unilateral approach, i.e., if an adenoma and a normal gland are identified, the contralateral side is not explored. We analyzed the strategy of the unilateral approach using a mathematical model to determine the variables that influence the probability of missing a tumor on the unexplored side of the neck. Assuming the frequency of single adenoma is 80%, hyperplasia 14%, double adenomas 4%, triple adenomas 1%, and carcinoma 1%, and the probability of missing a tumor on the explored side is 5%, we found that: 1. Only 41% of the patients treated by the unilateral approach undergo unilateral exploration. This is increased to 62% when a localization study with a sensitivity of 80% is used pre-operatively. 2. The probability of missing a tumor on the unexplored side of the neck parallels the prevalence of multiple adenomas. Half of the patients with triple adenomas and two-thirds of the patients with double adenomas will have a missed tumor when treated by the unilateral approach. 3. Patients who undergo unilateral exploration have an additional 7% to 8% probability of missing a tumor that would have been found if bilateral exploration is performed. This risk is lowered to 2% by a pre-operative localization study that is 80% sensitive. 4. A prospective study will require 684 patients, randomized to the unilateral or bilateral approach, to have an 80% statistical power (alpha = 0.05, beta = 0.20) of detecting a difference between a 5% and a 10% risk of missing a tumor.

Adenoma↗
PubMed1996

Treatment of distal ulcerative colitis with short-chain fatty acid enemas. A placebo-controlled trial. German-Austrian SCFA Study Group.

Rectal enemas containing a short-chain fatty acid mixture, butyrate alone, or saline placebo were administered to 47 patients with active distal ulcerative colitis. Enemas were instilled twice daily and the patients' condition was evaluated at entry and after four and eight weeks of local therapy. A disease activity index, chosen as the major end point, decreased significantly after all three modes of treatment with no difference among groups. The endoscopic appearance of the mucosa and the histologic degree of inflammation was not different among groups. After eight weeks, fewer colonic segments were affected endoscopically following butyrate than placebo treatment. This study showed trends towards a beneficial effect of topical short-chain fatty acids in active ulcerative colitis, but more patients are needed to demonstrate this effect with sufficient statistical power.

Adult↗
PubMed1982

[Prevention of coronary heart disease. A study of 2 rural communities of Zurich].

This study aimed at reducing risk factors for coronary heart disease through improving living habits in the population. It was conducted in a rural community in the canton of Zürich; a similar community without an intervention programme served for comparison. Data from questionnaires and examinations in random population samples examined at the start and a year later (1974-75) indicated that a favourable effect on smoking habits was achieved while blood-pressure levels were reduced in both communities, presumably because hypertensives were referred to their physician in the intervention as well as in the control area. Serum-cholesterol level and eating habits could not be demonstrably influenced. However, there was a trend toward weight reduction and an increase in physical activity in the intervention community. On comparing the initial findings, based on random samples, with an independent new sample examined at the end of the study, no overall changes in risk-factor levels could be found in the general population but the statistical power to show an effect is impaired by small numbers. The intensity of the intervention programme was limited by the available means; it was well accepted by the population.

Adult↗
PubMed1987

Pharmacokinetic drug interactions between digoxin and antiarrhythmic agents and calcium channel blocking agents: an appraisal of study methodology.

While preliminary screening for interactions between new cardiovascular pharmacotherapeutic agents and digoxin can be efficiently and safely conducted in normal healthy volunteers, it is particularly important to detect and quantify drug interactions in patients with varying degrees of cardiac, hepatic and/or renal dysfunction. Much of the previously published literature provides only minimal data to guide clinical practice because of limitations of study design including sample size and measurement techniques. Important factors that determine the ability of a particular study design to detect a drug interaction with digoxin include the accuracy and precision of the assay method for serum digoxin concentrations, intrasubject and intersubject variability in serum digoxin concentration, and sample size. The format of the trial (chronic versus single digoxin dosing in cardiac patients; chronic versus single digoxin dosing in normal subjects) and the method of assessment of alterations in digoxin handling (formal determination of digoxin clearance, comparison of multiple or single digoxin measurements during various phases of trial) also impact greatly on the clinical relevance of such investigations. Guidelines for future studies of drug interactions with digoxin in cardiac patients are proposed with particular emphasis on laboratory methods; measurement techniques during baseline, placebo, and active drug phases; calculation of the statistical power of the study; time course of the trial; and assessment of the clinical significance of the findings.

Anti-Arrhythmia Agents↗
PubMed1998

Prophylactic oophorectomy in colorectal carcinoma: preliminary results of a randomized, prospective trial.

UNLABELLED: Controversy exists regarding the role of prophylactic oophorectomy during resection for primary colorectal cancer. PURPOSE: A prospective, randomized trial was initiated to evaluate the influence of oophorectomy on recurrence and survival in patients with Dukes Stages B and C colorectal cancer. METHOD: Between November 1986 and March 1997, 155 patients were randomized to oophorectomy or no oophorectomy at laparotomy for resection of colorectal cancer. RESULTS: No incidence of gross or microscopic metastatic disease to the ovary was found among 77 patients randomized to oophorectomy, in contrast to previous reports. Preliminary crude survival curves suggested a survival benefit for oophorectomy between two and three years from surgery, but Kaplan-Meier survival analysis indicated that this was not statistically significant and the benefit does not appear to persist at five years. Kaplan-Meier curves of recurrence-free survival, however, suggest a more substantial separation of the curves, with 80 percent vs. 65 percent five-year disease-free survival for oophorectomy vs. nonoophorectomy, but further patient accrual is necessary to provide sufficient statistical power. CONCLUSIONS: Occult colorectal carcinoma metastatic to the ovaries has not been documented in this series of putative Dukes Stages B and C tumors. The possibility of a recurrence-free survival advantage emphasizes the need to continue this preliminary work.

Aged↗
PubMed1991

Effects of glucose on memory processes in young adults.

Recent studies suggest that glucose enhances memory in rodents and humans. The present experiment investigated the effects of glucose on memory performance and blood glucose changes in young adults (19-25 years). Subjects ingested (300 ml beverage) three doses of glucose (0, 30, 100 g) in a random, double-blind, triple crossover design. Thirty minutes post-glucose, subjects were shown nouns on a computer monitor and then administered recall and recognition memory tests. Blood samples were drawn at regular intervals. There was no effect of glucose on memory performance, and plasma glucose measures did not correlate with memory test scores. Statistical power was adequate to detect a medium effect. The results contradict the hypothesis that glucose enhances memory performance in young, healthy normal adults.

Adult↗
PubMed1992

Methodology of measuring the efficacy of antidepressants.

Evaluation of the efficacy of antidepressant agents needs to take into account factors which increase the "effect size", such as dosage, treatment duration, the use of two-phase trials, and pattern analysis of responders. Although many patients are thought to receive inadequate doses of antidepressants, relatively few dose-response studies have been performed. However, trials of both tricyclic antidepressants and phenelzine have shown that statistically significant improvements in outcome result from the use of higher dosages; the length of treatment may also affect results. In some studies, the proportion of patients showing a clear-cut response increased significantly among patients treated with active drug instead of placebo when the treatment period was extended from 4 to 6 weeks, independent of the dose used. There may thus be a distinct advantage in extending trials of antidepressants for a minimum of 6 weeks. Two-phase drug trials can be used to extend the trial period still further in responding patients, to emphasize the contrast between treatment and placebo effects and to eliminate type-2 errors. Twelve-week trials might increase the statistical power of the evaluation by 10-20%, in studies where the drug effect size is small. Pattern analysis of the timing and duration of patients' responses has been shown to aid the distinction of true responses from non-specific or placebo effects, and may be useful for evaluating data from studies of antidepressant agents which yield ambiguous results.

Antidepressive Agents↗
PubMed1996

Type I and type II error rates for quantitative trait loci (QTL) mapping studies using recombinant inbred mouse strains.

Effective mapping strategies for quantitative trains must allow for the detection of the more important quantitative trait loci (QTLs) while minimizing false positives. Type I (false-positive) and Type II (false-negative) error rates were estimated from a computer simulation of QTL mapping in the BXD recombinant inbred (RI) set compromising 26 strains of mice, and comparisons made with theoretical predictions. The results are generally applicable to other RI sets when corrections are made for differing strain numbers and marker densities. Regardless of the number or magnitude of simulated QTLs contributing to the trait variance, the p value necessary to provide adequate protection against both Type I (alpha=.0001) and Type II (beta=.2) errors, a QTL would have to account for more than half of the between-strain (genetic) variance if the BXD or similar set was used alone. In contrast, a two-step mapping strategy was also considered, where RI strains are used as a preliminary screen for QTLs to be specifically tested (confirmed) in an F2 (or other) population. In this case, QTLs accounting for approximately 16% of the between-strain variance could be detected with an 80% probability in the BXD set when alpha = 0.2. To balance the competing goals of minimizing Type I and II errors, an economical strategy is to adopt a more stringent alpha initially for the RI screen, since this requires only a limited genome search in the F2 of the RI-implicated regions (approximately 10% of the F2 genome when p < .01 in the RIs). If confirmed QTLs do not account in the aggregate for a sufficient proportion of the genetic variance, then a more relaxed alpha value can be used in the RI screen to increase the statistical power. This flexibility in setting RI alpha values is appropriate only when adequate protection against Type I errors comes from the F2 (or other) confirmation test(s).

Animals↗
PubMed1993

Differential effects of type 2 (non-insulin-dependent) diabetes mellitus on pentosidine formation in skin and glomerular basement membrane.

Pentosidine is an advanced Maillard/glycation reaction product the formation of which in human skin is significantly increased in Type 1 (insulin-dependent) diabetes mellitus and correlates with the severity of diabetic complications. Preliminary data in a limited number of Type 2 (non-insulin-dependent) diabetic individuals showed that skin pentosidine was not significantly elevated, raising the question of whether statistical power was insufficient for differences to be revealed, or whether pentosidine did not form because biological factors intrinsic to Type 2 diabetes affected the advanced Maillard reaction altogether. To resolve this question, pentosidine levels were measured in 209 human skin samples obtained at autopsy and in purified glomerular basement membranes from 45 subjects of various ages, with and without Type 1 and Type 2 diabetes and uraemia. Pentosidine increased exponentially in skin but curvilinearly in glomerular basement membranes, and reached 75 and 50 pmol/mg collagen at projected 100 years, respectively. Skin levels were not significantly elevated in individuals with Type 2 diabetes (p > 0.05). In contrast, pentosidine levels in glomerular basement membranes were elevated above the 95% confidence interval in the majority of diabetic patients regardless of the type of diabetes and in all individuals on haemodialysis. These data clearly demonstrate that the advanced Maillard reaction is indeed accelerated in Type 2 diabetes and strongly suggest that differences in pentosidine accumulation rates may be due to differences in collagen turnover. In diabetes and uraemia, accelerated Maillard reaction mediated protein crosslinking, as reflected by pentosidine, may contribute to decreased turnover of the extracellular matrix, sclerosis and thickening of basement membranes.

Adult↗
PubMed1995

Prevention of depression with primary care patients: a randomized controlled trial.

The prevention of major depression is an important research goal which deserves increased attention. Depressive symptoms and disorders are particularly common in primary care patients and have a negative impact on functioning and well-being comparable with other major chronic medical conditions. The San Francisco Depression Prevention Research project conducted a randomized, controlled, prevention trial to demonstrate the feasibility of implementing such research in a public sector setting serving low-income, predominantly minority individuals: 150 primary care patients free from depression or other major mental disorders were randomized to an experimental cognitive-behavioral intervention or to a control condition. The experimental intervention group reported a significantly greater reduction in depressive levels. Decline in depressive levels was significantly mediated by decline in the frequency of negative conditions. Group differences in the number of new episodes (incidence) of major depression did not reach significance during the 1-year trial. We conclude that depression prevention trials in public sector primary care settings are feasible, and that depressive symptoms can be reduced even in low-income, minority populations. To conduct randomized prevention trials that can test effects on incidence with sufficient statistical power, subgroups at greater imminent risk have to be identified.

Adolescent↗
PubMedDate not supplied

A role for hemispheric asymmetry in human behavioral variability.

A model is presented in which functional lateral specialization and selective hemisphere priming combine to provide a mechanism for behavioral variability. The model is tested and supported by two experiments in which lateral attentional priming produces significant reductions in between-subject and within-subject variability. These findings help us to understand the source of behavioral variability, broaden our knowledge of the gross structures and functions of the brain, provide information about the manipulation of perceived control, and offer a technique for increasing statistical power in a wide variety of research settings.

Adolescent↗
PubMed2002

Sentinel lymph node mapping and biopsy for breast cancer at a rural-based university medical center: initial experience with intraparenchymal and intradermal injection routes.

BACKGROUND: Recent data suggests that intradermal (ID) injection for sentinel lymph node (SLN) mapping and biopsy in breast cancer is as effective and reproducible as intraparenchymal (IP) injection. The aim of this study was to review our initial experience with IP and ID injection for SLN mapping and biopsy at our rural-based university medical center. METHODS: From January 4, 1999 to January 5, 2001, 113 of 165 patients with breast cancer underwent attempted SLN mapping and biopsy by either IP (n=63) or ID (n=50) injection. Selection of the IP versus ID injection route was non-randomized and based on surgeon preference. Success of SLN localization was examined. RESULTS: SLN localization was successful in 82% of IP and 100% of ID for radioisotope (p=0.001), 69% of IP and 92% of ID for blue dye (p=0.002), and 90% of IP and 100% of ID (p=0.024) for radioisotope and blue dye. Identical comparisons made after excluding the first 10 cases, 20 cases, and 30 cases from each injection group showed that the percentage of cases in each group in which the SLN localized changed minimally; however, some of the resultant p values eventually lost statistical significance. CONCLUSIONS: SLN localization was more successful by ID injection than by IP injection, thus favoring utilization of the ID injection route. The eventual loss of statistical power in some of the comparisons with increasing numbers of initial cases excluded may reflect differential learning curves of the two injection techniques; however, this may simply be a reflection of decreasing sample size used in each subsequent analysis. A prospective randomized trial comparing the IP and ID injection route may be warranted.

Academic Medical Centers↗