def METHOD_NAME(self) -> str:
    report = StringIO()
    contig_groups = sorted(self.counts.items())
    combined = defaultdict(Counter)
    for contig_name, contig_counts in contig_groups:
        for position, position_counts in list(contig_counts.items()):
            position_counts = Counter(position_counts)
            contig_counts[position] = position_counts
            combined[position] += position_counts
    if 1 < len(contig_groups):
        contig_groups.append(('Combined', combined))
    for contig_name, contig_counts in contig_groups:
        print(contig_name + ':', file=report)
        for position, position_counts in sorted(contig_counts.items()):
            position_counts = Counter(position_counts)
            report.write(f'{position}: ')
            coverage = sum(position_counts.values())
            position_display = []
            for nuc, nuc_count in position_counts.most_common():
                prevalence = f'{nuc_count/coverage:0.2f}'
                if prevalence != '0.00':
                    position_display.append(f'{nuc} ({prevalence})')
            print(*position_display, sep=', ', file=report)
    return report.getvalue()