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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

Farm-level prevalence distribution for VTEC O157 and F. hepatica for a single simulated synthetic dataset of 270 farms. Bottom row shows data after excluding farms with either 0% or 100% VTEC O157 sample prevalence.
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fig0005: Farm-level prevalence distribution for VTEC O157 and F. hepatica for a single simulated synthetic dataset of 270 farms. Bottom row shows data after excluding farms with either 0% or 100% VTEC O157 sample prevalence.

Mentions: For each of M = 90, 135, 180, 225 and 270 farms, we simulated 2500 fake datasets. Fig. 1 summarises a single simulation of 270 farms. The farm-level and individual-level infection prevalence figures are not identical to those specified because of random sample variation. We observe that a large number of farms have 0% infection for VTEC O157, and are therefore excluded prior to model fitting. The simulated datasets satisfied the desired attributes on average, as shown in Fig. 2. Of the 2500 datasets with 270 farms, the mean (standard deviation) of the farm-level and individual-level sample prevalence for VTEC O157 was 18.9% (2.4%) and 4.0% (1.0%) respectively. Similarly, for F. hepatica they were 79.9% (2.4%) and 20.0% (1.3%) respectively. The mean (standard deviation) of the average number of cows per farm across datasets was 27.1 (1.1) for the mean, and 23.4 (1.5) for the median.


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)

Farm-level prevalence distribution for VTEC O157 and F. hepatica for a single simulated synthetic dataset of 270 farms. Bottom row shows data after excluding farms with either 0% or 100% VTEC O157 sample prevalence.
© Copyright Policy - CC BY-NC-ND
Related In: Results  -  Collection

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

fig0005: Farm-level prevalence distribution for VTEC O157 and F. hepatica for a single simulated synthetic dataset of 270 farms. Bottom row shows data after excluding farms with either 0% or 100% VTEC O157 sample prevalence.
Mentions: For each of M = 90, 135, 180, 225 and 270 farms, we simulated 2500 fake datasets. Fig. 1 summarises a single simulation of 270 farms. The farm-level and individual-level infection prevalence figures are not identical to those specified because of random sample variation. We observe that a large number of farms have 0% infection for VTEC O157, and are therefore excluded prior to model fitting. The simulated datasets satisfied the desired attributes on average, as shown in Fig. 2. Of the 2500 datasets with 270 farms, the mean (standard deviation) of the farm-level and individual-level sample prevalence for VTEC O157 was 18.9% (2.4%) and 4.0% (1.0%) respectively. Similarly, for F. hepatica they were 79.9% (2.4%) and 20.0% (1.3%) respectively. The mean (standard deviation) of the average number of cows per farm across datasets was 27.1 (1.1) for the mean, and 23.4 (1.5) for the median.

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