能有效发现变量之间因果关系的研究方法是（  ）

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SQL Error: select id,body,options from ***_enewstiku where sourceid='31596' and id < 2530648 and id<>'2530648' order by id desc limit 5 SQL Error: select id,body,options from ***_enewstiku where sourceid='31596' and id > 2530648 and id<>'2530648' order by id asc limit 5