3、 Estimator(估计量) aA sample statistic used to guess a population parameter Example: Sample average for o selected residents is an estimator of the population mean of all77 386 residents Estimate [WRONG! Estimators are usually wrong. Often useful anyway a The actual number computed from the data Example: 33.91 is an estimate of neighborhood weekly food expenditures per person Estimation error:估计误差 a Estimator minus population parameter. Unknown o Example:3、Estimator（估计量）  A sample statistic used to guess a population parameter ⚫ Example: Sample average for 100 selected residents is an estimator of the population mean of all 77,386 residents Estimate [WRONG! Estimators are usually wrong. Often useful anyway]  The actual number computed from the data ⚫ Example: $33.91 is an estimate of neighborhood weekly food expenditures per person Estimation error:估计误差  Estimator minus population parameter. Unknown ⚫ Example: 33.91 – 35.69 = –1.78