Hi Allan:

Measuring efficacy can vary based on the definition of efficacy,  your measured variable and experimental design. If you Google  Abbott's Toxicity formula (Abbott 1925). You will find information about experiments that use this formula. The formula corrects for kill in the control. It is commonly used in toxicological studies till now.

Regarding field work, the efficacy has been calculated as follows:
Efficacy= (( % infest before treatment- %infest after treatment)/% infest before treatment))*100
The control is not consider at this time if you are looking at % kill caused by natural causes and as a result of a treatment. If you would like to consider taking out the natural kill you can use the top formula.

The most commonly used efficacy calculation for varroa control, it considers use of a finishing treatment using  a product that kills >95%. In this case the formula will be:
Efficacy = (number of mites killed by tested treatment/ (mites killed by treatment +mites killed by finishing treatment))*100

You might ask what is the value of control in this case? The value of control is to show that not all mites died naturally for one reason or other.

You can correct efficacy in this case by taking numbers from the calculated efficacy and apply once again Abbott's formula
Once you get to math and statistics, you have to be specific in asking the question and use the proper formula. It has also to be reported in the paper to make sure the reader knows what is reported.

Hope this helps.

Dr. Medhat Nasr
Alberta Provincial Apiculturist
Pest Surveillance Branch
Research and Innovation Division
Agriculture and Rural Development
17507 Fort Road NW
Edmonton, AB T5Y 6H3 Canada
Tel: 780-415-2314             Fax: 780-422- 6096
E-mail:  [log in to unmask]

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