On Sampling Error in Market Share Estimates*
重新表述了品牌市场份额常用估计量的相对误差，发现其受市场渗透率和品牌及品类销量变异影响，且不依赖于实际份额水平。使用健康产品行业数据表明，即使大样本下相对误差也可能很大，并给出了基于营销参数的上界。
ABSTRACT The relative error in the usual estimator of a brand's market share is reformulated in terms of marketing parameters. Such error is shown to be influenced in an important way by market penetration, as well as by variation in brand and product category volume. Of particular interest is the result that the relative error does not depend on the actual share level. Using data from a marketing research firm that supplies share estimates to the health products industry, we find that the relative error may be substantial even when a large sample is available. An upper bound on this relative error is obtained using marketing parameters that can frequently be measured using industry data and a company's internal records, thus reducing the level of judgmental input required in the planning of sample surveys.