Here is the design of a clinical trial:

Official Title: Spinal Manipulation and Patient Self-Management for Preventing Acute to Chronic Back

Included conditions:
- Acute Pain
- Low Back Pain, Mechanical

Study Armgroups:
- {'label': 'Supported-Self management (SSM)', 'type': 'EXPERIMENTAL', 'description': 'Supported-Self management', 'interventionNames': ['Behavioral: Supported-Self Management (SSM)']}
- {'label': 'Spinal Manipulation Therapy (SMT)', 'type': 'EXPERIMENTAL', 'description': 'Spinal Manipulation Therapy', 'interventionNames': ['Other: Spinal Manipulation Therapy (SMT)']}
- {'label': 'SMT + SSM', 'type': 'EXPERIMENTAL', 'description': 'Spinal Manipulation Therapy + Supported Self-Management', 'interventionNames': ['Combination Product: SMT + SSM']}
- {'label': 'Standard Medical Care (SMC)', 'type': 'ACTIVE_COMPARATOR', 'description': 'Standard Medical Care', 'interventionNames': ['Drug: Standard Medical Care (SMC)']}

Interventions:
- {'type': 'BEHAVIORAL', 'name': 'Supported-Self Management (SSM)', 'description': 'Provides low back pain sufferers opportunities to develop the capacity and motivation to self-manage their pain in an adaptive manner. This includes psychological/behavioral strategies, mind-body approaches, lifestyle advice, pain education and pain coping.', 'armGroupLabels': ['Supported-Self management (SSM)']}
- {'type': 'OTHER', 'name': 'Spinal Manipulation Therapy (SMT)', 'description': 'SMT will address the biological and physical aspects of low back pain (e.g. spinal dysfunction) with the intention of restoring maximum movement and functional ability of the spine.', 'armGroupLabels': ['Spinal Manipulation Therapy (SMT)']}
- {'type': 'COMBINATION_PRODUCT', 'name': 'SMT + SSM', 'description': 'Combination Treatment', 'armGroupLabels': ['SMT + SSM']}
- {'type': 'DRUG', 'name': 'Standard Medical Care (SMC)', 'description': "Guideline based medical care informed by the American College of Physicians' guidelines on noninvasive treatment for low back pain.", 'armGroupLabels': ['Standard Medical Care (SMC)']}

Primary Outcomes:
- {'measure': 'Average pain intensity over one year post-randomization', 'description': 'Measured using the 0-10 numerical rating scale (0=no LBP, 10=the worst LBP possible).', 'timeFrame': 'Weekly from enrollment - 52 weeks'}
- {'measure': 'Average disability over one year post-randomization', 'description': 'Measured using the Roland-Morris Disability Questionnaire (RMDQ), a 24-item questionnaire that measures the degree to which a low back problem restricts daily activities.', 'timeFrame': 'Measured monthly from enrollment - 52 weeks'}
- {'measure': 'Prevention of chronic low back pain (LBP) that is impactful at 10-12 months follow-up', 'description': 'Measured by the LBP impact scale which includes measures of pain intensity, pain interference, and physical function from the PROMIS-29 Profile v2.0. The scale ranges from 8 (least impact) to 50 (greatest impact).', 'timeFrame': 'Months 10 -12'}

Please estimate the sample size based on the assumption: 
The significance level is set at alpha = 0.05 with a multiple comparison correction for the two primary outcomes. The power is calculated based on 5000 simulations per scenario, with adjustments for period and site, and accounting for group imbalance. The trial assumes a 90% follow-up rate from an initial enrollment of 1000 participants.
Sample size and power
        The trial focuses on two separate effectiveness research questions with different time frames. First, we consider the overall time-averaged patient status for both pain and disability over the full 12 months of follow-up. We recognize the importance of considering multiple comparisons when evaluating both average pain and average function over one year, and we therefore adopt a multiple comparison correction for these two outcomes. Second, we consider the long-term impact of LBP using an assessment of impact over months 10â12. However, given the different focus of the major questions and the timing of assessments further adjustment for multiple comparisons across the two questions is not indicated. Sample size and power for the trial is based on these two effectiveness research questions. To characterize the power of our primary analyses (an overall ANOVA F-test) a summary table is provided that considers potential standardized mean differences comparing the individual intervention arms to medical care (see TableÂ 5). For a small effect size (Cohenâs d of 0.2) and an additive effect we have greater than 88% power to reject the null. However, additivity may not hold so we also consider sub-additive scenarios, in addition to scenarios where only one intervention is effective. For small to moderate effect size differences (0.25â0.35) we have >â80% power for all scenarios for LBP impact and most scenarios for pain and disability. We assume nâ=â1000 enrolled with 90% follow-up that yields 900 evaluated participants. Power is based on 5000 simulations per scenario with adjustment for period (4-arm, 2-arm) and site, and accounting for the group imbalance that results from our temporary restriction to 2-arm randomization (see trial modifications due to Covid page 11).
        
Table 5Standardized mean differences relative to medical care and powerScenarioSMT AloneSSM AloneSSMâ+âSMTPowerAverage pain intensity & disability over 12 months post-randomization(alphaâ=â0.05/2)Chronicity based on LBP impact averaged over months 10â12(alphaâ=â0.05)
Additive
0.200.200.4088%93%
Sub-Additive 1
0.250.250.3585%91%
Sub-Additive 2
0.300.300.3089%94%
Sub-Additive 3
0.250.250.2574%81%
Single effect 1a
00.300.3096%98%
Single effect 1b
0.3000.3088%94%
Single effect 2a
00.250.2583%91%
Single effect 2b
0.2500.2571%80%LBPâ=âLow Back Pain; SMTâ=âSpinal Manipulation Therapy; SSMâ=âSupported Self-Management