结论：青岛地区1987~2002年双生子出生比呈现上升趋势，有明显季节和地区分布差异。
Conclusion: The twin birth ratios of Qingdao ascends from 1987 to 2002. The difference in distribution and the seasonal variation are notable.
结论：青岛地区1987~2002年双生子出生比呈现上升趋势，有明显季节和地区分布差异。
Conclusion: The twin birth ratios of Qingdao ascends from 1987 to 2002. The difference in distribution and the seasonal variation are notable.
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