A hospital laundry changed its detergent, and the share of linen bundles turned back by the ward inspector for staining fell from twelve per cent to four per cent. The laundry supervisor argues that the new detergent lifts stains better than the old one. Which of the following, if true, most strengthens the supervisor's argument?

A drop in rejections can come from cleaner linen or from a slacker inspection, and the second is the rival that must be closed off. One inspector applying one unchanged standard removes it, and unchanged incoming linen removes the possibility that the wards simply sent lighter soiling. What is left is the detergent. Container size, the laundry's coverage and the smell of the product settle nothing.