When doing testing for efficacy, the results are given in the Concentration needed along with the Time needed to kill the organism. This is the CT value.
For example, the Flu bug I mentioned earlier has a CT of 5000. If you have a concentration of 500 PPM chlorine dioxide, you would need to maintain that concentration in contact with the flu virus for at least 10 minutes for a 100% kill. If you had a concentration of 10 PPM, you would have to maintain contact for 500 minutes to achieve the same results.
Knowing the CT value allows you to design an effective concentration that is reasonable to use in your application.