We are trying to do a randomized controlled trial on patients. For a certain diseases patients, we want to know whether or not intervention improves their quality of life or not. We're dividing the patients into two groups: one receive the traditional method, other receives the intervention where their vitals and labs are checked with responses to some questionnaires about their quality of life is collected in 2 weeks, 4 weeks, 3 months, and 6 months. Whereas, for the traditional method, we're only going to follow up with patient in 1 month and 6 months. The lab and vitals for the traditional methods are only taken at 6 months.
For this, we'd like to know the power and sample size of the study. I would like to either know how to calculate it, or would like to know what I must know before I ask statistician's help. I read Cohen's article A Power Primer which help me make some sense, but I'm still somewhat confused about effect size