Here is the design of a clinical trial:

Official Title: The Effect of Joint Transition Visits on Quality of Life in Adolescents With Inflammatory Bowel Diseases: a Protocol for a Prospective, Randomized, Multicentre, Controlled Trial (TRANS-IBD)

Included conditions:
- Inflammatory Bowel Diseases
- Crohn's Disease
- Ulcerative Colitis

Study Armgroups:
- {'label': 'Joint visits', 'type': 'EXPERIMENTAL', 'description': 'Subjects in the intervention arm attend a total of four joint transition visits performed with the participation of both the adult and the pediatric gastroenterologist.', 'interventionNames': ['Other: joint visits']}
- {'label': 'Usual care', 'type': 'NO_INTERVENTION', 'description': "Adolescents meet only the pediatric gastroenterologist, but there is a balanced consultation between the two gastroenterologists with respect the patient's treatment plan."}

Interventions:
- {'type': 'OTHER', 'name': 'joint visits', 'description': 'The intervention is the implementation of joint transition visits with the participation of both the pediatric and the adult gastroenterologist. One-year intervention period was chosen. In total, there are four joint visits every third months for the adolescents aged 17-18. Each joint visit lasts for at least for 20 minutes, although in case of complex medical history, there is no restriction with respect to the length of the visit. Joint transition visits 1, 2 and 3 (V1-3) are led by the pediatric gastroenterologist, and visit 4 (V4) is led by the adult gastroenterologist.', 'armGroupLabels': ['Joint visits']}

Primary Outcomes:
- {'measure': 'Change in patient reported health-related quality of life (HRQoL) one year after transfer', 'description': 'HRQoL is measured with a validated and IBD-specific questionnaire, called IMPACT III (HR) (unabbreviated scale title is not existing). It consists of 35-items, using a five-point Likert self-completed response scale. The questions are related to the severity and frequency of the following symptoms over the last two weeks: bowel symptoms, systemic symptoms, emotional functioning, social functioning, body image and treatments or interventions. The lowest score is 35, that can be achieved, and the maximum is 175 points. Higher scores indicate better HRQoL.', 'timeFrame': '24 months'}

Please estimate the sample size based on the assumption: 
21% drop-out rate, 80% power, and 95% significance level
Sample size
        Sample size calculation was based on the article of Cohen et al and was performed by the biostatistician team of the Institute of Translational Medicine.54 Based on the available data, we expect nine points difference between the mean IMPACT-III points of the intervention and control group at the end of the study. In order to detect this difference between the two study groups, 160 patients are needed to be recruited (80/group) using a 21% drop-out rate, 80% power and 95% significance level.