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The feasibility of testing whether Fasciola hepatica is associated with increased risk of verocytotoxin producing Escherichia coli O157 from an existing study protocol.

Hickey GL, Diggle PJ, McNeilly TN, Tongue SC, Chase-Topping ME, Williams DJ - Prev. Vet. Med. (2015)

Bottom Line: We simulate data under the framework of a mixed-effects logistic regression model in order to calculate the power to detect an association effect size (odds ratio) of 2.In order to reduce the resources required for such a study, we exploit the fact that the test results for VTEC O157 will be known in advance of testing for F. hepatica by restricting analysis to farms with a VTEC O157 sample prevalence of >0% and <100%.From a total of 270 farms (mean 27 cows per farm) that will be tested for VTEC O157, power of 87% can be achieved, whereby testing of F. hepatica would only be necessary for an expected 50 farms, thus considerably reducing costs.

View Article: PubMed Central - PubMed

Affiliation: Department of Epidemiology and Population Health, Institute of Infection and Global Heath, University of Liverpool, The Farr Institute@HeRC, Waterhouse Building, 1-5 Brownlow Street, Liverpool L69 3GL, UK. Electronic address: graeme.hickey@liverpool.ac.uk.

No MeSH data available.


Related in: MedlinePlus

Power curve to detect an odds ratio of 2 (equivalently β = log(2)) for a positive F. hepatica test for varying number of farms available for testing. The horizontal axis denotes the total number of farms undergoing VTEC O157 testing, with the actual number of farms undergoing F. hepatica testing shown in parentheses.
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fig0015: Power curve to detect an odds ratio of 2 (equivalently β = log(2)) for a positive F. hepatica test for varying number of farms available for testing. The horizontal axis denotes the total number of farms undergoing VTEC O157 testing, with the actual number of farms undergoing F. hepatica testing shown in parentheses.

Mentions: The power curve is shown in Fig. 3. It shows that from a synthetic dataset of 270 farms included in the FSA survey, only 50 farms on average, equating to an average of 1645 pat samples, would have a sample VTEC O157 prevalence of >0% or <100% and thus require testing for F. hepatica. This would yield power of 87% to detect an odds ratio of 2, hence there is potential to test fewer farms. Repeating the exercise with 225 farms, we find that we expect to apply fluke testing to 42 farms, equating to approximately 269 fewer pat sample tests, whilst yielding power of 82%.


The feasibility of testing whether Fasciola hepatica is associated with increased risk of verocytotoxin producing Escherichia coli O157 from an existing study protocol.

Hickey GL, Diggle PJ, McNeilly TN, Tongue SC, Chase-Topping ME, Williams DJ - Prev. Vet. Med. (2015)

Power curve to detect an odds ratio of 2 (equivalently β = log(2)) for a positive F. hepatica test for varying number of farms available for testing. The horizontal axis denotes the total number of farms undergoing VTEC O157 testing, with the actual number of farms undergoing F. hepatica testing shown in parentheses.
© Copyright Policy - CC BY-NC-ND
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4401447&req=5

fig0015: Power curve to detect an odds ratio of 2 (equivalently β = log(2)) for a positive F. hepatica test for varying number of farms available for testing. The horizontal axis denotes the total number of farms undergoing VTEC O157 testing, with the actual number of farms undergoing F. hepatica testing shown in parentheses.
Mentions: The power curve is shown in Fig. 3. It shows that from a synthetic dataset of 270 farms included in the FSA survey, only 50 farms on average, equating to an average of 1645 pat samples, would have a sample VTEC O157 prevalence of >0% or <100% and thus require testing for F. hepatica. This would yield power of 87% to detect an odds ratio of 2, hence there is potential to test fewer farms. Repeating the exercise with 225 farms, we find that we expect to apply fluke testing to 42 farms, equating to approximately 269 fewer pat sample tests, whilst yielding power of 82%.

Bottom Line: We simulate data under the framework of a mixed-effects logistic regression model in order to calculate the power to detect an association effect size (odds ratio) of 2.In order to reduce the resources required for such a study, we exploit the fact that the test results for VTEC O157 will be known in advance of testing for F. hepatica by restricting analysis to farms with a VTEC O157 sample prevalence of >0% and <100%.From a total of 270 farms (mean 27 cows per farm) that will be tested for VTEC O157, power of 87% can be achieved, whereby testing of F. hepatica would only be necessary for an expected 50 farms, thus considerably reducing costs.

View Article: PubMed Central - PubMed

Affiliation: Department of Epidemiology and Population Health, Institute of Infection and Global Heath, University of Liverpool, The Farr Institute@HeRC, Waterhouse Building, 1-5 Brownlow Street, Liverpool L69 3GL, UK. Electronic address: graeme.hickey@liverpool.ac.uk.

No MeSH data available.


Related in: MedlinePlus