I'm part of a team of medical doctors designing a study. but nobody seems to get statistics and the study might result in a huge waste of time, so that's why I'm here.
Our pediatric patients suffer from a heart disease. We clinically noticed that they have a reduction of pulmonary function. We would want to know if a pulmonary screening is needed for these patients.
Our plan is to run pulmonary tests on patients (two or three times, in different days, since the test can have some variability) and on healthy controls matched by age (we will probably end up with 10:7 patients:controls).
Reference ranges for pulmonary tests are determined based on sex, weight etc. and results of the tests are expressed as % of predicted value. A test is considered pathological if the result is < x% than predicted (x varies from test to test).
There are two issues that bug me.
1) Patients are at different stages of the disease, so I do not know if a normal test means that the disease has no pulmonary effect or if it's just at an early stage.
2) Puberty, oh damn puberty, screws up everything and we will probably end up having to divide our sample into prepubescent-pubescent-postpubescent.
Does the design of the study make sense?
How do we determine the sample size needed?