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PubMed2006

A fresh look at growth assessment of infants and young children in the Czech Republic in context of international developments.

The growth charts of basic body measurements are an important aid for the daily routine practice of paediatricians. Charts for children from birth to 2 years of age form an integral component of a set of such tools for the age spectrum from birth to 18 years of age. The interpretation of growth charts is highly dependent on the data on basis of which the charts were constructed. In the Czech Republic, the growth reference data have been regularly updated since 1951, in 10-year intervals. These updates are based on data from nation-wide anthropological surveys of children and adolescents. Countries, which do not have their own reference data, have been using for growth assessment the 1977 World Health Organization (WHO) and the National Center for Health Statistics (NCHS) international reference growth charts. These charts, developed for height for age, weight for age, and weight for height, were based for children younger than 2 years on a longitudinal study of North American children. Over the years, use in practice showed that because of the original criteria used to select the child population studied, these reference growth charts were not suitable for assessing growth of breastfed children. The 1977 reference is based on predominantly artificially, that is formula-fed, child population. The evidence shows that breastfed and artificially fed infants grow differently and that the growth pattern of breastfed children most likely better reflects physiological growth. In 1994, based on the accumulated evidence, the WHO started working on new international standards which would be based on a sample of healthy breastfed children. The project, the WHO Multicentre Growth Reference Study (MGRS), was carried out from 1997-2003. It focused on collection of growth and development data of 8440 children from different ethnic and cultural groups. The underlying assumption of the project was that in favourable socio-economic conditions and with a recommended level of nutrition and lack of maternal smoking, children's growth is very similar, regardless of their ethnic origin and geographic location. The new growth standard for children 0-5 years of age will be available early in 2006. In the Czech Republic, we plan to analyse our national reference against this standard. If considered necessary, a process will be put in place for replacing the Czech reference with the WHO standard. The objective of this article is to alert health professionals that growth charts currently used in their country may not represent an optimal tool, especially with regard to the assessment of nutritional status for 0 to 2-year-old children, unless already based on data of breastfed children. Generally, the lack of awareness of the difference between the two growth patterns--the breastfed versus artificially fed child--poses a serious problem since a strict interpretation of the growth charts may lead to early supplementation of breastmilk with infant formula and/or premature introduction of complementary foods. Both of these practices tend to lead to premature cessation of breastfeeding, one of the key strategies to improve child health and development.

Anthropometry↗
PubMed2004

A randomized, placebo-controlled trial of 5% and 2% topical minoxidil solutions in the treatment of female pattern hair loss.

BACKGROUND: To pical minoxidil solution 2% stimulates new hair growth and helps stop the loss of hair in men with androgenetic alopecia and women with female pattern hair loss. Results can be variable, and historic experience suggests that higher concentrations of topical minoxidil may enhance efficacy. OBJECTIVE: The purpose of this 48-week, double-blind, placebo-controlled, randomized, multicenter trial was to compare the efficacy and safety of 5% topical minoxidil with 2% topical minoxidil and placebo in the treatment of female pattern hair loss. METHODS: A total of 381 women (18-49 years old) with female pattern hair loss applied 5% topical minoxidil solution (n = 153), 2% topical minoxidil solution (n = 154), or placebo (vehicle for 5% solution; n = 74) twice daily. Primary efficacy variables were change in nonvellus hair count at week 48, and patient and investigator assessments of change in hair growth/scalp coverage at week 48. RESULTS: After 48 weeks of therapy, 5% topical minoxidil was superior to placebo for each of the 3 primary efficacy measures. The 2% topical minoxidil group demonstrated superiority over placebo for hair count and investigator assessment of hair growth/scalp coverage at week 48; differences in patient assessment of hair growth at week 48 were not significantly different from placebo. The 5% topical minoxidil group demonstrated statistical superiority over the 2% topical minoxidil group in the patient assessment of treatment benefit at week 48. Both 5% and 2% topical minoxidil helped improve psychosocial perceptions of hair loss in women with female pattern hair loss. An increased occurrence of pruritus, local irritation, and hypertrichosis was observed with 5% topical minoxidil versus 2% topical minoxidil and placebo. CONCLUSION: In this 48-week study of 381 women with female pattern hair loss, 5% topical minoxidil was superior to placebo on each of the 3 primary efficacy end points: promoting hair growth as measured by change in nonvellus hair count and patient/investigator assessments of hair growth and scalp coverage. Application of 2% topical minoxidil was superior to placebo for assessments of nonvellus hair counts and investigator assessment of hair growth/scalp coverage at week 48; differences in patient assessment of hair growth at week 48 were not significantly different from placebo. At week 48, the 5% topical minoxidil group demonstrated statistical superiority over the 2% topical minoxidil group in the patient assessment of treatment benefit. Both concentrations of topical minoxidil were well tolerated by the women in this trial without evidence of systemic adverse effects. With the introduction of numerous herbal remedies for hair loss, of which most have not been tested in randomized, double-blind, placebo-controlled trials, it is important to describe well-controlled trials that demonstrate the efficacy and safety of topical drugs.

Administration, Topical↗
PubMed1999

A simple way to estimate the median time and compare survival distributions in analgesic trials under informative censoring.

We discuss the problem of estimating the median time and comparison of survival curves when data are nonrandomly censored in analgesic trials. In these trials patients experience post-surgical pain at the time of randomization. Time to onset of analgesia is measured by patient-administered stopwatches. An effective analgesic is one for which the median time to onset is "short." The study design allows patients to remedicate if their pain persists, and this remedication prior to pain relief censors the time-to-onset measures. The time to onset for patients who remedicate is nonrandomly censored. Assuming noninformative censoring yields misleading results with the Kaplan-Meier method (for estimation of median time) and the log-rank test (for comparison of survival curves). This assumption can also obscure the superior effect of an effective analgesic over an ineffective one. We propose a simple and intuitive way to handle the nonrandomly censored data in analgesic trials in order to (a) estimate the median time to pain relief and (b) compare the survival distributions between treatments. The method proposed is applied to data collected from an acute pain clinical trial, and the results are discussed.

Analgesics↗
PubMed2006

Instruments for causal inference: an epidemiologist's dream?

The use of instrumental variable (IV) methods is attractive because, even in the presence of unmeasured confounding, such methods may consistently estimate the average causal effect of an exposure on an outcome. However, for this consistent estimation to be achieved, several strong conditions must hold. We review the definition of an instrumental variable, describe the conditions required to obtain consistent estimates of causal effects, and explore their implications in the context of a recent application of the instrumental variables approach. We also present (1) a description of the connection between 4 causal models-counterfactuals, causal directed acyclic graphs, nonparametric structural equation models, and linear structural equation models-that have been used to describe instrumental variables methods; (2) a unified presentation of IV methods for the average causal effect in the study population through structural mean models; and (3) a discussion and new extensions of instrumental variables methods based on assumptions of monotonicity.

Bias↗
PubMed2000

Non-parametric covariance methods for incidence density analyses of time-to-event data from a randomized clinical trial and their complementary roles to proportional hazards regression.

The principal response criteria for many clinical trials involve time-to-event variables. Usual methods of analysis for this type of response criterion include product-limit estimators of cumulative survival for the treatment groups, (stratified) logrank tests to compare treatments, and proportional hazards regression models with treatment and relevant covariates. When adjustment for covariates is of some importance, the relative roles of these methods may be of some concern, particularly for confirmatory clinical trials which must provide convincing findings to regulatory agencies. Unadjusted methods may have lower power, but there are issues regarding adjustment for covariates that may be controversial. These issues include applicability of proportional hazards assumptions, whether the correct model has been specified, and whether there is parallelism between treatments for relationships with covariates. One way to address these issues is to use non-parametric analysis of covariance strategies with extensions to log incidence density estimation. The principal basis for this method is no association between covariates and treatment groups as provided by randomized assignment of patients to groups. The background theory and strategies for computation are described for this method. Aspects of its application are illustrated for a clinical trial with two treatment groups and 722 patients. The objective of analysis for this clinical trial is evaluation of treatment effects with and without adjustment for 22 a priori covariates and a stratification for three geographical regions.

Disease Progression↗
PubMed2006

Stochastic inequality probabilities for adaptively randomized clinical trials.

We examine stochastic inequality probabilities of the form P (X > Y) and P (X > max (Y, Z)) where X, Y, and Z are random variables with beta, gamma, or inverse gamma distributions. We discuss the applications of such inequality probabilities to adaptively randomized clinical trials as well as methods for calculating their values.

Artificial Intelligence↗
PubMed2004

A method for analyzing longitudinal outcomes with many zeros.

Health care utilization and cost data have challenged analysts because they are often correlated over time, highly skewed, and clumped at 0. Traditional approaches do not address all these problems, and evaluators of mental health and substance abuse interventions often grapple with the problem of how to analyze these data in a way that accurately represents program impact. Recently, the traditional 2-part model has been extended to mixed-effects mixed-distribution model with correlated random effects to deal simultaneously with excess zeros, skewness, and correlated observations. We introduce and demonstrate this new method to mental health services researchers and evaluators by analyzing the data from a study of assertive community treatment (ACT). The response variable is the number of days of hospitalization, collected every 6 months over 3 years. The explanatory variable is group: ACT vs. standard case management. Diagnosis (schizophrenia vs. bipolar disorder), time, and the baseline values of hospital days are covariates. Results indicate that clients in the ACT group have a higher probability of hospital admission, but tend to have shorter lengths of stay. The mixed-distribution model provides greater specification of a model to fit these data and leads to more refined interpretation of the results.

Adult↗
PubMed1999

Establishing equivalence by showing that a specified percentage of the effect of the active control over placebo is maintained.

We propose a procedure for establishing equivalence that determines whether a specified percentage of the treatment effect of a known active agent over placebo is maintained. This procedure accounts for the error in the estimates from the historical studies of the known active agent and placebo as well as the error in the estimates from the equivalence study of the new test treatment versus the active control. After the procedure is presented, it is compared analytically to a procedure in which the equivalence boundary is estimated from historical data and then used with a one-sided test. We address sample size requirements for the proposed equivalence procedure. We also illustrate the use of the proposed procedure with an example from the clinical area of thrombolytic therapy in acute myocardial infarction.

Data Interpretation, Statistical↗
PubMed2005

Treatment comparisons for a partially categorical outcome applied to a biomarker with assay limit.

The plasma level of HIV-RNA has been shown to be a strong prognostic biomarker for clinical progression and death in HIV infected patients and is widely used as the primary outcome in clinical trials to evaluate antiretroviral treatments. Currently approved assays to measure HIV-RNA levels have a lower limit of reliable quantification (LoQ). Current regulatory guidelines recommend using the proportion of patients achieving HIV-RNA levels below the assay limit at a certain time point (e.g. 24 or 48 weeks) as the primary endpoint for regulatory approval. However, a substantial decrease in HIV-RNA that does not go below the LoQ still is considered clinically beneficial for patients with advanced diseases who have failed many other therapies and are unlikely to maximally suppress the virus and achieve HIV-RNA levels below the LoQ. An experimental treatment may not be distinguishable from a control solely in terms of the proportions of patients whose HIV-RNA levels fall below the LoQ. The sensitivity of the comparison between the experimental treatment and the control could be increased by considering as well the difference between the treatments with respect to the HIV-RNA reductions of patients not achieving HIV-RNA levels below the LoQ. In this paper, we introduce a best-rank analysis which assigns the best rank to patients who achieve the HIV-RNA levels below the LoQ and applies the Mann-Whitney-Wilcoxon rank test to compare the two treatment groups. The Mann-Whitney-Wilcoxon statistic is shown to be a weighted sum of two statistics: one to compare the proportions of patients achieving the HIV-RNA levels below the LoQ and one to compare the viral reductions in patients with HIV-RNA levels above the LoQ. The corresponding statistical null and alternative hypotheses and the clinical interpretations of this best-rank test procedure are also discussed. An example is used to illustrate this approach and a simulation study is used to compare this approach with other methods.

Anti-HIV Agents↗
PubMed1999

Expressing estimators of expected quality adjusted survival as functions of Nelson-Aalen estimators.

Quality adjusted survival has been increasingly advocated in clinical trials to be assessed as a synthesis of survival and quality of life. We investigate nonparametric estimation of its expectation for a general multistate process with incomplete follow-up data. Upon establishing a representation of expected quality adjusted survival through marginal distributions of a set of defined events, we propose two estimators for expected quality adjusted survival. Expressed as functions of Nelson-Aalen estimators, the two estimators are strongly consistent and asymptotically normal. We derive their asymptotic variances and propose sample-based variance estimates, along with evaluation of asymptotic relative efficiency. Monte Carlo studies show that these estimation procedures perform well for practical sample sizes. We illustrate the methods using data from a national, multicenter AIDS clinical trial.

Acquired Immunodeficiency Syndrome↗
PubMed2004

Perceptions of nursing faculty regarding ethical issues in nursing research.

A major premise of any research activity is that ethical conduct will be identified and observed during the research process. Yet a comprehensive review of the nursing literature failed to find any research assessing nurses' perceptions of ethical issues related to authorship, publication, reporting results, or funding. This study assessed nursing faculty members' perceptions of ethical scenarios related to the areas of authorship, publication, reporting results, and funding. A 34-item questionnaire, consisting of ethical issues related to research, was mailed to a national random sample of nursing faculty who were teaching at graduate degree-granting institutions. A three-wave mailing was used to maximize response rate. A total of 388 nurses responded to the survey (77.6% response rate). Less than half of the respondents reported that content included in their curriculum was related to the issues under study. Respondents' perceptions of the ethical scenarios varied. A majority of the respondents considered six of the scenarios ethical, eight unethical, one questionable, and one not an ethical issue. Five of the scenarios received widely varied responses. Faculty members who had chaired student dissertations found three questionnaire items significantly (p < .05) more unethical than faculty members who had not chaired dissertations. Faculty teaching in programs in which the highest degree offered was a doctorate found two items unethical significantly more often than faculty teaching at programs in which the highest degree offered was a master's degree. Results of this study demonstrate the potential that students are not being taught necessary issues related to ethical authorship and publication practices. Faculty members themselves may not have had the education needed to educate their own students in the area of research ethics.

Analysis of Variance↗
PubMed2002

A seminar series in applied biostatistics for clinical research fellows, faculty and staff.

Familiarity with experimental design and statistical analysis techniques is necessary for investigators to conduct state-of-the-art research in clinical medicine. A wide range of options for biostatistical training is available. These include formal academic courses for credit, one-on-one education offered under the guise of consultation, self-paced textbook or computer learning, intensive short courses, portions of extended courses spanning an assortment of other subjects, and a continuing series of seminars or lectures covering selected topics in statistics. The latter structure is described in this article. We offered an eight-week lecture series focusing on a new topic in biostatistics each week. The course targeted clinical faculty, postdoctoral fellows, residents, and other interested research staff at a large medical research institution. The series focused on interpretation of medical journal articles with regard to statistical issues. Another objective was to provide information to increase a participant's expertise in the design of research studies. Guidance was offered for effective communication with collaborating biostatisticians. The format and contents of the seminar series are described. Aspects of the course that proved to be successful are discussed.

Biometry↗
PubMed2000

Practical guidelines for multiplicity adjustment in clinical trials.

Multiplicity in clinical trials may appear under several different guises: multiple endpoints, multiple treatment arm comparisons, and multiple looks at the data during interim monitoring, to name a few. It is well recognized by statisticians and nonstatisticians alike that multiplicity inflates the type I error rate of the experiment, and this has prompted the development of many multiple comparison adjustment procedures. What has remained one of the thornier and more controversial points of contention among trialists today is the philosophy surrounding the need for multiplicity adjustment in clinical trials. This paper provides guidelines on how to deal with this complex issue in a practical manner. Through a series of scenarios and examples, we illustrate the fundamental issues surrounding the concept of multiplicity and point to some key questions one should ask when deliberating on the necessity and extent of adjustment for multiple comparisons. Control Clin Trials 2000;21:527-539

Bias↗