def estimate_cluster_size(cluster_info, days_since) -> str:
    """Estimate the size of the next cluster"""
    clusters_ago = -1
    seizure_text = "The next cluster"
    if days_since < 2:
        # Possibly still in a cluster
        clusters_ago = -2
        seizure_text = "This cluster"
    last_cluster_size = cluster_info.iloc[clusters_ago].number
    if last_cluster_size <= 3:
        # Last cluster was smaller
        return f"{seizure_text} is anticipated to be a large one, usually around 6 seizures"
    else:
        return f"{seizure_text} is anticipated to be a small one, usually 3 or less"