(a) National annual prices and diagnostic variables based on at least two data collections are required except where a single collection (e.g. housing) is suitable. Collection can be limited to major cities if data are available to extrapolate prices to national levels;
(a) 国家年度价格和调查分析变数必须以进行至少两次数据收集所得数据为依据，进行一次数据收集便足够（如住房）的情况除外。