To: WormMail list (recip. undisclosed). WormMail.201103251000. Drench Efficacy Calculators – UPDATE!
UPDATE 2015-03-30. The RESO calculator has been updated (2013, by RJ Dobson), plus some of the links below are now dead due to the purchase then closure of Posterous by Twitter.
Here are updated links:
RESO-Dobo Mod Like Dr Leo Le Jambre (CSIRO, Armidale), Dr Rob Dobson (formerly CSIRO, now Murdoch Univ., Perth WA) has a modified version of Angus Cameron’s original ‘RESO_FECR4”, getting around one or two issues I mentioned in WormMail 20110323 (below).
Here, with permission, is Rob Dobson’s version of RESO along with some comments:
Here is a version of RESO that does not have problems with 100% efficacy i.e. when all the post-treatment counts are zero (i.e. you don’t get the “#DIV/0!” problem in the output). It was also modified to allow the Lower Confidence Limit (LCL) to take –ve estimates (e.g. if the LCL= -50% then egg counts could have increased by 50%?). It may seem logical to truncate the LCL at 0% but I think if the data is so poor that we can not really tell if the counts have decreased or increased then the confidence limits should reflect that level of uncertainty!
Finally I am not happy with RESO when efficacy is 100% because the LCL=UpperCL=100% i.e. it does not really provide confidence limits for 100% efficacy. This is most definitely WRONG as some FECRT are more reliable than others. I have worked out a fix for this but have not got around to implementing it, maybe soon.
I would also strongly urge all efficacy results to be reported to the client with their accompanying confidence limits.
Comments: Unless they have changed recently, the Industry and Investment NSW (formerly Primary Industries/Dept Ag) Vet Lab at Menangle reports CLs as well as estimates of (arithmetic) mean Worm Egg Count Reduction% for treatment groups in a DrenchTest (Worm Egg Count Reduction Trial (WECRT, aka FECRT)).
For those not initiated into the black arts of statistics, Confidence Limits give you an idea of the signal-to-noise ration with data and associated stats…or, if you like, they tell you the range within which the ‘true’ mean WECR% (as opposed to the estimated/calculated mean) is likely to fall.
Resistance is said to exist if the reduction in the arithmetic mean from the drench groups is less than 95% (when compared with those from untreated sheep at day 10-14 or the treated group prior to treatment), and in which the lower 95% confidence limit is less than 90% reduction level. (Hutchinson GW- Australia and New Zealand Standard Diagnostic Procedures, page 41 February 2009 – see SCAHLS website). – SL
Amy Tranzillo (Pfizer, New York) drew my attention to calculators of a different sort. The website mentioned and related websites is worth a look; there is even a short clip of Dave Leathwick talking about resistance and combinations. Things just keep getting better. 🙂
HI Steve –
Hope you are doing well. We also have a Drench efficacy calculator for the farmer, we developed out of our Pfizer New Zealand office. It is definitely not as sophisticated as these 2 but more of a quick tool for farmers to use to understand the connection between drench effectiveness and production losses.
Yes the only other New Yorker on your distribution list – Tony Simon is now a Parisian!
Sr. Manager, Global New Products Marketing │Pfizer Animal Health
—– Forwarded by S L on 25/03/2011 09:57 AM —–
Date: 23/03/2011 04:58 PM
Subject: Drench Efficacy Calculators
To: WormMail List (recip. undisclosed) WormMail.20110323 Drench Efficacy Calculators Here are a couple of calculators that might be of interest/use to some of you.
Leathwick drench efficacy calculator (Updated link. See the top of this post. SL, 2015-03-30).
The first is from Dr David Leathwick, AgResearch NZ.
He tells me he made it ‘for a couple of vets who couldn’t do the maths’. (Correct: David is not a vet 🙂 He is an entomologist cum gun parasitologist and black belt martial artist).
He says it is free to those who might be find it useful but with the usual disclaimers (no guarantees, use it at your own risk etc…).
I think it is rather nice. If you know the drench efficacy for certain (single) actives, the calculator will work out efficacy for various other actives and also combinations of actives.
If nothing else, it is an educational tool.
RESO Calculator (Updated 2013. See link at top of this post. SL, 2015-03-30).
The second is also an Excel-based calculator, but this one is for calculating drench efficacies and 95% Confidence Limits for raw egg count data from a Worm Egg Count Reduction Test (aka WECRT, Faecal Egg count Reduction Test (FECRT), or DrenchTest).
This calculator was created by veterinary epidemiologist Angus Cameron (a vet who could do maths) based on an earlier program (The ‘RESO’ program. See spreadsheet for credits).
The RESO calculator or variations of it are used by various labs to analyse results from a WECRT. Importantly it also gives you 95% Confidence Limits for each estimate of mean Worm Count Reduction%.
I think Leo Le Jambre had a slightly modified version of the RESO calculator (to get around a problem with calculations when all the egg counts in a group were zero??).
I suggest you should not modify or distribute these without reference to the original authors.
Well done, Bot. 🙂