Version 1

The sample weights are essential for computing national estimates. Each sample weight represents the inverse of the probability of selection of the case. The sample weight has been adjusted for hospital non-response within each NEISS-AIP sample stratum and changes in the number of ED visits annually in the sampling frame of US hospital EDs. More details are given in the Sample Design and Implementation Report. Two sample weights are provided. WEIGHT is the sample weight that was assigned to each case. WEIGHTA is an annualized weight that was calculated as 2*WEIGHT for 2000 data and 1*WEIGHT for 2001 and after. Since data collection did not begin until July 2000, the 2000 data file only has 6 months of data. Therefore, WEIGHTA was created as a way to get annualized national estimates. If the user is going to analyze national estimates based on data combined from the 2000 and 2001/2002 data files, WEIGHTA should be used to weight the data. If the user is going to analyze national estimates based on data from the 2001 through 2015 data files ONLY, then either WEIGHT or WEIGHTA can be used because these variables are identical. Using the 2000 data for temporal trend analysis is not recommended because no adjustment was made for seasonality.样本权重（sample weights）对于全国性估计值的计算至关重要。每一样本权重对应个案被抽中概率的倒数。该样本权重已针对各NEISS-AIP抽样层内的医院无应答情形，以及美国医院急诊室（Emergency Department, ED）抽样框架内的年度急诊就诊人次变化完成调整。更多细节可查阅《抽样设计与实施报告（Sample Design and Implementation Report）》。本次共提供两类样本权重：WEIGHT为分配至每个个案的基础样本权重；WEIGHTA为年度化权重，其中2000年数据的WEIGHTA取值为2*WEIGHT，2001年及后续年份数据的WEIGHTA取值为1*WEIGHT。由于数据采集直至2000年7月才正式启动，2000年数据集仅包含6个月的观测数据。为此，WEIGHTA被设计用于生成年度化的全国估计值。若用户需将2000年数据与2001/2002年数据合并开展全国估计值分析，则应使用WEIGHTA对数据进行加权处理。若用户仅针对2001年至2015年的数据集开展全国估计值分析，则可任选WEIGHT或WEIGHTA，因该时间段内二者取值完全一致。不建议使用2000年数据开展时间趋势分析，因其未针对季节性因素进行调整。