Hello,
I am conducting some preliminary concentration-fixing steps on a pesticide used for house fly larvae. My initial data from 4 initial concentrations came out like this: highest conc. - 12/20 dead, second highest - 10/20 dead, third highest - 7/20 dead, fourth highest - 3/20 dead, control 4/20 dead. When I do Abbott's correction on the fourth highest, I get a negative value. Do I simply not use Abbott's correction at all for any of these concentrations, or do I count the fourth highest response as 0/20? Thanks in advance!
I Duly agree with @ Prof. Udikeri,
According to the WHO,
If the control mortality is above 20%, the tests must be discarded. When control mortality is greater than 5% but less than 20%, then the observed mortality has to be corrected using Abbot's formula. Also, If the control mortality is below 5%, it can be ignored and no correction of test is necessary whereas mortality of ≥5% requires correction.
For more information, You can follow the below link.
http://apps.who.int/iris/bitstream/10665/250677/1/9789241511575-eng.pdf
Therefore, in my view, you should repeat the procedure again to get authenticated result.
Hi Edwin,
I suggest you to do for the fourth dose (3/20) as 0/20 and for the control as 0/20. You have also to correct for the other doses.
Try this and see if there have biological mean...
You have to discard the data of the treatment which which gives negative corrected mortality. Usually the mortality should not be > 5% in control. Otherwise whole set-up goes unacceptable.
Hello Edwin, what you should do is to use the lowest mortality i. e. 3 as your control mortality instead of the 4 you used in the Abbott formula.
I Duly agree with @ Prof. Udikeri,
According to the WHO,
If the control mortality is above 20%, the tests must be discarded. When control mortality is greater than 5% but less than 20%, then the observed mortality has to be corrected using Abbot's formula. Also, If the control mortality is below 5%, it can be ignored and no correction of test is necessary whereas mortality of ≥5% requires correction.
For more information, You can follow the below link.
http://apps.who.int/iris/bitstream/10665/250677/1/9789241511575-eng.pdf
Therefore, in my view, you should repeat the procedure again to get authenticated result.
(similar question from colleague Edwin, if anyone could give me a hint, I would appreciate!! )
Hi,
I'm performing dose-response experiments in mites testing different substances by contact. I saw some guidelines where is not necessary to perform mortality correction if mortality in solvent control is
Hi Ms. Lima,
1) Could be natural variability. I wouldn't worry about it. If it does worry you though, I'd replicate the dose response trials a few more times and hope the natural variability works out to a more predictable response.
2) Again, I would replicate more dose response trials. Can I ask how many replicates you've done so far? how many doses? How many individuals per dose?
Dr. B.
You need to repeat your experiment.Control treatment should be 5% mortality or less. In few cases can be around 10%.In rare cases can be 20% or less. Salam and best regards .
Provided that other things are ok, the negative values after the correction should not be a worry, because you can transform it with neglog transformation.
Hi Ted
I think you are facing two problems apart from the criteria specific for the application of Abbott's correction to the data:
1. The replicates are so small that any accidental effects from your experimental technique will produce large swings in outcome ratios. Consequently, as colleagues have suggested you need to perform more replications and, given the small group sizes you are working with, I would suggest a minimum of five replications of each test/control even at the initial screen stage.
2. You need to consider, subject to the outcome of your repetition tests, that perhaps your insecticide delivery vehicle is exerting a significant component of activity. So perhaps you need to look at alternative solvents or media for delivery of the insecticide.
As for the outcome and interpretation of the data after Abbott's correction you need to apply comon sense. If a treatment consistently results in lower mortality than the control there are possibly other factors operating. From a mortaltiy effect aspect the treatment needs to be rejected and really based on plain numbers irrespective of the correction this would show as a negative. What you need to think about is that, if this is for example the lowest dose of the "active" compound it may be that it has the opposite effect from the one intended. A good example that you might like to consider: strychnine is a neurotoxin, like many insecticides, but in ultra low doses it is a neurostimulant and used to be used in so called "nerve tonics" that were popular around 50 years ago. Similar effects can be observed with some metabolic poisons. So the point I am making is that perhaps your dose ranging is telling you something important about the cut-off levels for activity, which in the case of house fly larvae could be critical because in the harsh environments where they develop degradation of insecticides occurs readily so if your active is reduced below a certain dose concentration level it could act as a maggot growth enhancer rather thna having its desired effect.
Best wishes
Ian
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