Biomedical subjects

Pascal Minini

Publications and source records attributed to Pascal Minini.

4 recordsLinked to original sources

PubMed2004

Sensitivity analysis of longitudinal normal data with drop-outs.

We propose to perform a sensitivity analysis to evaluate the extent to which results from a longitudinal study can be affected by informative drop-outs. The method is based on a selection model, where the parameter relating the dropout probability to the current observation is not estimated, but fixed to a set of values. This allows to evaluate several hypotheses for the degree of informativeness of the drop-out process. Expectation and variance of missing data, conditional on the drop-out time are computed, and a stochastic EM algorithm is used to obtain maximum likelihood estimates. Simulations show that when the drop-out parameter is correctly specified, unbiased estimates of the other parameters are obtained, and coverage percentages of their confidence intervals are close to their theoretical value. More interestingly, misspecification of the drop-out parameter does not considerably alter these results. This method was applied to a randomized clinical trial, designed to demonstrate non-inferiority of an inhaled corticosteroid in terms of bone density, compared with a reference treatment. Sensitivity analysis showed that the conclusion of non-inferiority was robust against different hypotheses for the drop-out process.

Adolescent↗

PubMed2004

[Multiplicity of inferences in clinical trials: adjustment methods, clinical interpretation issues].

Multiplicity of inferences is present in a large majority of clinical trials and conducts to false analyses or interpretation issues. The main risk consists in false positive conclusions. A large number of statistical methods is available for controlling the rate of false positive conclusions. But formal adjustment is not necessary in all cases and depends on the aims of the study.

Clinical Trials as Topic↗

PubMed2004

Sensitivity analysis of longitudinal binary data with non-monotone missing values.

This paper highlights the consequences of incomplete observations in the analysis of longitudinal binary data, in particular non-monotone missing data patterns. Sensitivity analysis is advocated and a method is proposed based on a log-linear model. A sensitivity parameter that represents the relationship between the response mechanism and the missing data mechanism is introduced. It is shown that although this parameter is identifiable, its estimation is highly questionable. A far better approach is to consider a range of plausible values and to estimate the parameters of interest conditionally upon each value of the sensitivity parameter. This allows us to assess the sensitivity of study's conclusion to assumptions regarding the missing data mechanism. The method is applied to a randomized clinical trial comparing the efficacy of two treatment regimens in patients with persistent asthma.

Adrenal Cortex Hormones↗

PubMed2003

Long-term safety of fluticasone propionate and nedocromil sodium on bone in children with asthma.

OBJECTIVE: Inhaled corticosteroids are recommended as first-line therapy for pediatric asthma. However, few controlled long-term studies have investigated their effect on bone mineral density (BMD) and growth. METHODS: Children who were aged 6 to 14 years and had persistent asthma were randomized to 24 months' treatment with fluticasone propionate (FP) 200 micro g/d or nedocromil sodium (NS) 8 mg/d (if uncontrolled, maximum doses of 400 micro g/d and 16 mg/d, respectively). BMD was assessed blind and analyzed at a central facility on the basis of dual-energy x-ray absorptiometry measurements of the lumbar spine and femoral neck at months 0, 6, 12, and 24. Height was measured at months 0, 12, and 24. Efficacy parameters (lung function, asthma control, occurrence of exacerbations) were measured every 3 months. RESULTS: In total, 174 children were randomized to treatment (87 received FP, and 87 received NS). At month 24, the adjusted mean percentage increase in lumbar spine BMD was 11.6% in the FP group compared with 10.4% in NS-treated children (95% confidence interval for treatment difference: -0.7% to 3.1%). The corresponding increases in femoral neck BMD were 8.9% and 8.5%, respectively. There was no significant difference in growth between the 2 groups: adjusted mean growth rates were 6.1 cm/y with FP and 5.8 cm/y with NS. FP was significantly superior for every efficacy parameter investigated and was similarly well tolerated as NS. CONCLUSIONS: The long-term effects of FP and NS on BMD accrual and growth are similar among children with asthma. The benefit:risk ratio of FP may be considered superior to that of NS.

Administration, Inhalation↗