Chest Physiotherapy and Cystic Fibrosis: Conclusion
With a level of significance of 0.05 (type 1 error), a typical power of 0.85 (type 2 error), an inherent variability of 15 percent and a difference of 10 percent between treatments to be regarded as clinically significant—using paried t tests—the sample size required would be 23 subjects. Increasing the power to 0.95 in this case would require a sample size of 32 subjects (SigmaStat, Jan-del Scientific; San Raphael, Calif). Sample size therefore is an essential consideration in evaluating the reliability and power of statistical analysis.
Most studies evaluating CPT treatments in CF patients fail to indicate the statistical power of the study or the size of the change required to be statistically significant and most have sample sizes of less than 20. Hence, the literature becomes even more difficult to interpret in view of sample size and statistical power, particularly those studies where no significant difference was shown between modalities.
Chest physiotherapy is generally accepted as a routine part of the medical management of CF patients. Despite the extensive array of literature concerning the effects of various physiotherapy regimens, the most effective form of CPT treatment has yet to be conclusively proven. Interpretation and analysis of the results of these studies is difficult due to technical, methodologic, and statistical factors. There is a great need for improvements in experimental research design if future studies of the effects of CPT on CF patients are to yield useful and reproducible results. Techniques need to be specifically defined, statistical power needs to be considered and made explicit in publications, results need to be analyzed by commonly available severity scoring systems, longitudinal studies including compliance variables are required, and appropriate measuring systems are necessary. Given the variance inherent in CF such as severity of disease, treatment compliance, airway lability, adjunctive medications, and the presence of concomitant disease, it may be more appropriate to consider which physiotherapy regimens are more effective for individual patients rather than any one technique being the most effective for all patients with cystic fibrosis.