Limits...
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 as a function of the odds ratio (OR) for detection under the alternative hypothesis. The analysis is based on first performing VTEC O157 testing on all M = 270 farms.
© Copyright Policy - CC BY-NC-ND
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4401447&req=5

fig0020: Power curve as a function of the odds ratio (OR) for detection under the alternative hypothesis. The analysis is based on first performing VTEC O157 testing on all M = 270 farms.

Mentions: We simulated 2500 synthetic datasets under alternative hypothesis effect sizes of β = log(1.2), log(1.4), …, log(2.0), …, log(3.0), in each case with the maximum number of farms available for testing (M = 270). In each case we recalculated the random-effects distribution parameters to match the marginal VTEC O157 farm-level prevalence. Power ranged from 13.0% (for OR = 1.2) to 99.6% (for OR = 3.0) (Fig. 4). The power to detect an OR of 1.8 would be 75%.


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 as a function of the odds ratio (OR) for detection under the alternative hypothesis. The analysis is based on first performing VTEC O157 testing on all M = 270 farms.
© Copyright Policy - CC BY-NC-ND
Related In: Results  -  Collection

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

fig0020: Power curve as a function of the odds ratio (OR) for detection under the alternative hypothesis. The analysis is based on first performing VTEC O157 testing on all M = 270 farms.
Mentions: We simulated 2500 synthetic datasets under alternative hypothesis effect sizes of β = log(1.2), log(1.4), …, log(2.0), …, log(3.0), in each case with the maximum number of farms available for testing (M = 270). In each case we recalculated the random-effects distribution parameters to match the marginal VTEC O157 farm-level prevalence. Power ranged from 13.0% (for OR = 1.2) to 99.6% (for OR = 3.0) (Fig. 4). The power to detect an OR of 1.8 would be 75%.

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