Here is the design of a clinical trial:

Official Title: Registration Study of Natural History and Clinical Characteristics of Amyotrophic Lateral Sclerosis (ALS) in Mainland China

Included conditions:
- Amyotrophic Lateral Sclerosis

Study Armgroups:

Interventions:

Primary Outcomes:
- {'measure': 'Effective Survival', 'description': 'The length of time from the date of diagnosis to patient death or tracheotomy or ventilator-assisted breathing.', 'timeFrame': 'through study completion, an average of 3 month'}

Please estimate the sample size based on the assumption: 
Not explicitly stated in the provided paragraph.
Study sites and sample sizes
        This study will be performed at centres spread across approximately 20 provinces, four municipalities and four autonomous regions in mainland China (figure 2). At least one tertiary first-class hospital from each of the participating provinces will take part in the study. A total of 88 hospitals will be involved.
        
          Figure 2
          
            Regions of mainland China with centres participating in CHALSR. NA, not available.
          
          
        
        According to the pilot study, the median of patients diagnosed with ALS and completing the detailed clinical follow-ups in our participating hospitals is 18 per year. Thus, based on clinical experience, the total number of patients included in this 3-year study is theoretically estimated to reach 4752. The leading research institution formulating the overall study design is PUTH, which is the largest ALS centre in China, with an ALS cohort of more than 2000 patients and approximately 500 newly diagnosed ALS patients per year.22