A student decided to investigate just how effective washing with soap is in eliminating bacteria. To do this she tested four different methods—washing with water only, washing with regular soap, washing with antibacterial soap (ABS), and spraying hands with antibacterial spray (AS) (containing 65% ethanol as an active ingredient). Her experiment consisted of one experimental factor, the washing Method, at four levels.
She suspected that the number of bacteria on her hands before washing might vary
considerably from day to day. To help even out the effects of those changes, she generated
random numbers to determine the order of the four treatments. Each morning, she washed
her hands according to the treatment randomly chosen. Then she placed her right hand on
a sterile media plate designed to encourage bacteria growth. She incubated each plate for
2 days at 36°C, after which she counted the bacteria colonies. She replicated this procedure 8 times for each of the four treatments.