An analysis of eight 95 per cent confidence intervals for a ratio of Poisson parameters when events are rare

Visualizing regional myocardial blood flow in the mouse

RATIONALE

The spatial distribution of blood flow in the hearts of genetically modified mice is a phenotype of interest because derangements in blood flow may precede detectable changes in organ function. However, quantifying the regional distribution of blood flow within organs of mice is challenging because of the small organ volume and the high resolution required to observe spatial differences in flow. Traditional microsphere methods in which the numbers of microspheres per region are indirectly estimated from radioactive counts or extracted fluorescence have been limited to larger organs for 2 reasons; to ensure statistical confidence in the measured flow per region and to be able to physically dissect the organ to acquire spatial information.

OBJECTIVE

To develop methods to quantify and statistically compare the spatial distribution of blood flow within organs of mice.

METHODS AND RESULTS

We developed and validated statistical methods to compare blood flow between regions and with the same regions over time using 15-µm fluorescent microspheres. We then tested this approach by injecting fluorescent microspheres into isolated perfused mice hearts, determining the spatial location of every microsphere in the hearts, and then visualizing regional flow patterns. We demonstrated application of these statistical and visualizing methods in a coronary artery ligation model in mice.

CONCLUSIONS

These new methods provide tools to investigate the spatial and temporal changes in blood flow within organs of mice at a much higher spatial resolution than currently available by other methods.

Review: analysis of parasite and other skewed counts

OBJECTIVE

To review methods for the statistical analysis of parasite and other skewed count data.

METHODS

Statistical methods for skewed count data are described and compared, with reference to a 10-year period of Tropical Medicine and International Health (TMIH). Two parasitological datasets are used for illustration.

RESULTS

The review of TMIH found 90 articles, of which 89 used descriptive methods and 60 used inferential analysis. A lack of clarity is noted in identifying the measures of location, in particular the Williams and geometric means. The different measures are compared, emphasising the legitimacy of the arithmetic mean for the skewed data. In the published articles, the t test and related methods were often used on untransformed data, which is likely to be invalid. Several approaches to inferential analysis are described, emphasising (1) non-parametric methods, while noting that they are not simply comparisons of medians, and (2) generalised linear modelling, in particular with the negative binomial distribution. Additional methods, such as the bootstrap, with potential for greater use are described.

CONCLUSIONS

Clarity is recommended when describing transformations and measures of location. It is suggested that non-parametric methods and generalised linear models are likely to be sufficient for most analyses.

Safety of formoterol in patients with asthma: combined analysis of data from double-blind, randomized controlled trials

BACKGROUND

Concerns exist that regular long-acting beta(2)-adrenergic agonist (LABA) therapy may increase the risk of serious asthma-related events.

OBJECTIVE

To assess risks of formoterol-containing versus non-LABA treatment by using a large asthma database.

METHODS

This analysis included all blind, parallel-arm, randomized, active-controlled and/or placebo-controlled AstraZeneca-sponsored asthma studies with formoterol-containing and non-LABA comparator arms. Serious adverse events were assessed for inclusion in all-cause death, asthma-related death, asthma-related intubation, and asthma-related hospitalization categories by using blind adjudication. Data were combined across trials; relative risk (RR) was assessed by using Mantel-Haenszel methods.

RESULTS

Data were from 13,542 formoterol-randomized and 9968 non-LABA patients 4 years or older (42 trials), of whom 93% and 89%, respectively, received inhaled corticosteroid as part of randomized treatment or allowed medication. Incidence of all-cause death was low (n=3 and n=4, respectively), with numerically lower all-cause deaths/1000 patient-treatment years in the formoterol-treated group (0.53) versus the non-LABA group (0.82) (RR, 0.64; 95% confidence interval [CI], 0.14-2.92). No asthma-related deaths and 1 asthma-related intubation (formoterol-treated group) occurred. Asthma-related hospitalizations/1000 patient-treatment years were lower numerically in the formoterol-treated group (12.1) versus the non-LABA group (16.4) (RR, 0.73; 95% CI, 0.54-1.01), with fewer study discontinuations in the formoterol-treated group (12.7% vs 15.4%, respectively; RR, 0.79; 95% CI, 0.74-0.85). Relative to non-LABA, increasing daily formoterol dose (>/=4.5, 9, 18, 36 mug) did not increase the rate or incidence of asthma-related hospitalization.

CONCLUSION

No evidence of increased risk of asthma-related hospitalization, no asthma-related deaths, and a low incidence of all-cause death and asthma-related intubation were seen with formoterol-containing versus non-LABA treatment.

Safety of budesonide/formoterol maintenance and reliever therapy in asthma trials

BACKGROUND

The safety of long-acting beta(2)-agonists (LABAs) in asthma is debated. This study examined the safety of the inhaled corticosteroid (ICS)/LABA combination budesonide/formoterol dry powder inhaler used as maintenance and reliever therapy versus combination treatments based on guideline recommendations.

METHODS

Safety data from six double-blind, randomised clinical trials (RCTs) in asthma where budesonide/formoterol was used as maintenance and reliever therapy for at least 6 months were reviewed (N=14 346). All-cause mortality and asthma-related serious adverse events (SAEs) (co-primary endpoints), overall and cardiac SAEs, and discontinuations due to adverse events (DAEs) were assessed. Estimated Mantel-Haenszel (MH) relative risks (RR) with this regimen versus comparators were calculated.

RESULTS

There was no increase in all-cause mortality with budesonide/formoterol maintenance and reliever therapy (four deaths [0.07%] versus nine [0.10%]; pooled MH RR 0.70, 95% confidence interval [CI] 0.21-2.30). Asthma-related SAEs were reduced with budesonide/formoterol maintenance and reliever therapy: 41 (0.73%) versus 121 (1.38%); pooled MH RR 0.59, 95% CI 0.42-0.85. All-cause and asthma-related DAEs were also reduced with budesonide/formoterol maintenance and reliever therapy: pooled MH RR 0.60 (95% CI 0.46-0.79) and 0.43 (0.28-0.68), respectively. Overall and cardiac-related SAEs were comparable between treatment groups: pooled MH RR 0.96 (95% CI 0.82-1.14) and 1.26 (0.72-2.22), respectively.

CONCLUSION

Budesonide/formoterol dry powder inhaler maintenance and reliever therapy was well tolerated in RCTs versus fixed-dose alternatives and not associated with increased risk of death or cardiac-related SAEs and DAEs, and asthma-related SAEs and DAEs were significantly reduced. Given the limitations of RCTs, particularly exclusion of patients with co-morbidities, ongoing surveillance is appropriate.