3.11 11. An experiment was performed to determine if a new technician was proficient in performing a critical test used to evaluate the effectiveness of vacuum cleaners. The test procedure is to uniformly distribute 100g of dirt consisting of fine stones, sand, and talc over two square yards of test carpet. The dirt is then rolled into the carpet with a 25 pound roller for three minutes. Finally, the carpet is vacuumed for three minutes using a prescribed motion and rate. The recovered dirt in grams is determined from the weight change of the filter bag before and after the vacuuming step. Test carpets are vacuumed aggressively and weighed between trials to guarantee that they are clean before the dirt is applied. To demonstrate the new (2) technician's proficiency his recovery was compared to that of an experienced (1) technician for eight different carpet samples. For the new technician to be considered proficient, the mean recovery difference between the technicians must be less than 4g with 90% confidence. The recovery data were: Plush Multi-level Shag Level-loop 1 2 Technician 1 2 1 2 1 2 12 55.3 54.4 58.2 65.0 23.5 25.7 56.1 55.6 61.2 63.3 23.6 27.7 76.3 70.5 74.9 | 69.6

Fig: 1