In a study to see how reliable cadaver dogs are in detecting death:
In this study, there were 100 carpet contaminated and 100 uncontaminated carpet samples. Sensitivity showed that 75-100% of contaminated samples were identified correctly, and there were only 0-9% false positive hits for the uncontaminated samples. (I believe this is per dog - different dogs, different %)
This also means that 91-100% negatives were correctly identified, and there were 0-25% false negatives for positive samples.
http://dogsdontlie.com/main/2008/12/cadaver-dogs-how-reliable-are-they-at-detecting-death/
This is only for cadaver dogs, and I haven't found any studies on tracking dogs yet. I'll keep looking.