関連ワード:  what are the two methods of sampling    what are the different methods of sampling    what are the two types of sampling    what are the two types of sampling techniques    what are the different methods of sampling in statistics    what are the two types of sampling errors    what are the two types of sampling bias    what are the two types of sampling used by cr units    what are the two types of sampling in research    what are the different methods of sampling in research