Here is the design of a clinical trial:

Official Title: Implementing Telehealth Support to Increase Physical Activity in Girls and Women With Rett Syndrome

Included conditions:
- Rett Syndrome

Study Armgroups:
- {'label': 'Waitlist-Control Group', 'type': 'EXPERIMENTAL', 'description': "The 'waitlist control' group will receive the 12-week non-intervention period first, followed by 12 week intervention period.", 'interventionNames': ['Behavioral: Telehealth-delivered participation strategies to increase physical activity']}
- {'label': 'Immediate Treatment', 'type': 'EXPERIMENTAL', 'description': "The 'immediate treatment' group will receive the 12-week intervention period first, followed by 12 week non-intervention period.", 'interventionNames': ['Behavioral: Telehealth-delivered participation strategies to increase physical activity']}

Interventions:
- {'type': 'BEHAVIORAL', 'name': 'Telehealth-delivered participation strategies to increase physical activity', 'description': 'Therapists and primary caregivers will meet online on 6 occasions at fortnightly intervals over a 12 week period. Sessions will enable the development of strategies that will aim to increase the amount the participant stands and walks. Throughout, the therapists and primary caregivers will discuss physical activity needs, determine relevant activities, modify the program as necessary and plan additional goals.', 'armGroupLabels': ['Immediate Treatment', 'Waitlist-Control Group']}

Primary Outcomes:
- {'measure': 'Average daily uptime (%)', 'description': 'Percentage of time spent active (uptime) over total awake time, measured with an ActivPAL', 'timeFrame': 'Average over 4 days, data capture at baseline, after 12 weeks and after 24 weeks'}
- {'measure': 'Average daily step count', 'description': 'Number of daily steps measured by Stepwatch Activity Monitor', 'timeFrame': 'Average over 4 days, data capture at baseline, after 12 weeks and after 24 weeks'}

Please estimate the sample size based on the assumption: 
The response is normally distributed with an SD of 11%. The significance level is 0.05, the power is 0.8, and there is an allowance for dropout.
Sample size
          In preliminary Danish data,32 the response of individuals to the physical activity programme (per cent of sedentary behaviour) in a repeated measures design was normally distributed with an SD of 11%. If the true reduction, following the intervention, in the mean per cent of sedentary time is 5% and assuming a pairwise correlation of 0.5, we will need to study 50 individuals in a two-sample trial to be able to reject the null hypothesis that this response difference is 0, with probability (power) 0.8. The type I error probability associated with this test of the null hypothesis is 0.05. We will recruit 60 families, allowing for some dropout. A total of 26 individuals will be recruited from Australia, 14 from Denmark and 20 from Israel.