Here is the design of a clinical trial:

Official Title: Promoting Habit Formation in Family Physical Activity

Included conditions:
- Physical Activity

Study Armgroups:
- {'label': 'Control', 'type': 'NO_INTERVENTION', 'description': 'The control group package will consist of the Canadian 24 Hour Movement Guidelines recommending 60 minutes of moderate to vigorous physical activity per day for children. The guide also contains arguments \\& information about the benefits of physical activity.'}
- {'label': 'Family physical activity Planning', 'type': 'EXPERIMENTAL', 'description': 'Behavoural: Family Physical Activity Planning. The physical activity planning intervention condition will receive the same guidelines as the standard education control group but will also be provided with family physical activity planning material. This material will include workbook on how to plan for family physical activity; brainstorming exercises for parents \\& children where they list physical activities that they have found fun in the past, as well as some new activities they would like to try \\& skill training content to help with goal setting \\& tracking of physical activity.', 'interventionNames': ['Behavioral: Family Physical Activity Planning']}
- {'label': 'Family Physical Activity Habit Formation', 'type': 'EXPERIMENTAL', 'description': 'Behavioural: Family Physical Activity Habit formation. The Habit formation intervention condition will receive the same content as the education control condition and the physical activity planning condition but with additional material on creating physical activity support habits. The material includes a brief discussion of what habits are with some very straightforward examples such as preparing for sleep routines or initiating to drive a car to work. A key component of the habit section will be based on planning for context-dependent repetition, with pointers on how to maintain repetition as habit forms.', 'interventionNames': ['Behavioral: Family Physical Activity Habit Formation']}

Interventions:
- {'type': 'BEHAVIORAL', 'name': 'Family Physical Activity Planning', 'description': 'Families will receive the same guidelines as the standard education control group but will also be provided with family physical activity planning material. This material will include a skill training content workbook on how to plan for family physical activity. The material includes a brainstorming exercise for parents where they list physical activities they think their children have found fun in the past, as well as activities that they would find enjoyable to do as a family. We will provide this material as prompts/suggestions. Families will be instructed to plan for "when," "where," "how," and "what" physical activity will be performed \\& then track their physical activity. These aspects will be re-introduced and discussed at week 6 and week 12 in booster sessions', 'armGroupLabels': ['Family physical activity Planning']}
- {'type': 'BEHAVIORAL', 'name': 'Family Physical Activity Habit Formation', 'description': 'Families will receive the same content as the education control condition and the physical activity planning condition but with additional material on creating physical activity support habits. A key component of the habit section will be based on planning for context-dependent repetition, with pointers on how to maintain repetition as habit forms. The importance of creating cues for parental support of child physical activity is then outlined. Cues will also be considered factors that a) can precede the support activity but b) not be present very often when the activity is not to be performed. We will suggest that cues that have repeated exposure during times when family physical activity is not present Parents will then be asked to brainstorm and create a plan of consistency and cues with the workbooks provided. These aspects will be re-introduced and discussed at week 6 and week 12 in booster sessions.', 'armGroupLabels': ['Family Physical Activity Habit Formation']}

Primary Outcomes:
- {'measure': "Change from baseline in children's physical activity to 6 months", 'description': "Children's physical activity will be quantified by accelerometry. Children will wear an accelerometer for a minimum of 10 hours per day for 7 days at baseline and 6 months. Additionally this measure will assess intermediate outcomes at 6 weeks and 3 months.", 'timeFrame': 'Baseline & 6 months'}

Please estimate the sample size based on the assumption: 
four measurement occasions, three conditions, duration of 6 months, within-person variance of 1.0
Statistical power and sample size
        Given the hierarchical nature of the data (ie, the four measurement occasions at level-1 were considered to be nested within the participant at level-2), the OpDes Program for power estimation of hierarchical linear models90 was used. With a frequency of four measurement occasions, three conditions, a duration of 6 months as the primary end-point, within-person variance of 1.0, a growth rate of 1.0 and a small effect size (d=0.30â0.40), a minimum of 150 families with a goal of 240 families (ie, 50â80 children per condition) are needed to show significant difference in PA accelerometry (minutes of MVPA primary outcome) by condition over time. The effect size represents the findings from our prior intervention research with this demographic18 22 and considering our pilot study on habit formation,36 yet it is clearly in the range for the detection of differences between the PLANNING and HABIT conditions.91 92