Phenol coefficient - this is the ratio of the effect of the antimicrobial agent compared to a similar concentration of phenol:

Concentration of Antimicrobial Compound = Phenol Coefficient
        Same Concentration of Phenol

A compound that has a phenol coefficient greater than 1 is more effective than phenol.  Since phenolics are caustic to skin and mucus membranes, any agent that has a greater antimicrobial effect under lower concentrations and less toxicity is generally favored.

Use-dilution - small metal cylinders are soaked in bacterial cultures of Pseudomonas aeruginosa, Staphylococcus aureus and Salmonella cholerasuis var. typhimurium.  Each cylinder is placed into different concentrations (dilutions) of a test disinfectant and left to incubate for 10 minutes.  The cylinders are then removed, rinsed with sterile water and placed in sterile nutrient broth.  The broths are incubated at 37 oC for 48 hours.  If the broth is cloudy following incubation, the compound is not effective.  Among the broths that are free of microbial growth, the researcher will choose the one that (a) is best at controlling all three species (if possible) and (b) is the lowest effective concentration.

In-use - phenol coefficient and use dilution can give valid results when performed properly, but may be misleading since both utilize only a small number of microbes that may or may not represent the population on any given surface.  The in-use test involves taking test swabs of surfaces and equipment before and after disinfection, which, while taking longer than the other tests, gives a more realistic result for the given environment that is tested.