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7-study-design [2018/08/01 16:10] thorsten [7.5 Sampling design] |
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| __**7.1-7.6 are likely NOT relevant for passive surveillance components. But for any component design, readers should refer to 7.7 and 7.8.**__\\ \\ At this step, a surveillance designer should carefully consider how the study population is going to be selected. Should a census be performed (testing all animals in the target population) or is the population going to be subjected to some type of selective sampling strategy? Even if a census is to be performed, one may still want to consider some information in this section, such as the number of units in the population, as they are important to plan data collection. Moreover, if the target units are clustered (for instance animals clustered in farms), and a census at the top level will be performed (census of herds for instance), sampling within clusters (animals within farms) may still need to be designed.\\ \\ | __**7.1-7.6 are likely NOT relevant for passive surveillance components. But for any component design, readers should refer to 7.7 and 7.8.**__\\ \\ At this step, a surveillance designer should carefully consider how the study population is going to be selected. Should a census be performed (testing all animals in the target population) or is the population going to be subjected to some type of selective sampling strategy? Even if a census is to be performed, one may still want to consider some information in this section, such as the number of units in the population, as they are important to plan data collection. Moreover, if the target units are clustered (for instance animals clustered in farms), and a census at the top level will be performed (census of herds for instance), sampling within clusters (animals within farms) may still need to be designed.\\ \\ | ||
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| ===== 7.1 Point of sample collection ===== | ===== 7.1 Point of sample collection ===== | ||
| Addressed in the surveillance components overview. Please see page “**__[[/2-Surveillance-components|2- Overview of surveillance components]]__**”.\\ \\ | Addressed in the surveillance components overview. Please see page “**__[[/2-Surveillance-components|2- Overview of surveillance components]]__**”.\\ \\ | ||
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| ===== 7.2 Selection of units: census or sampling ===== | ===== 7.2 Selection of units: census or sampling ===== | ||
| \\ Sampling is the focus of the next section. However, the selection of units (whether all the target population defined can be reached - census - or a sampling design will be applied) should consider carefully the availability of a sampling frame. If it is not possible to identify and locate farms/herds/flocks, a surveillance designer should consider where else animals can be located and sampled.\\ \\ | \\ Sampling is the focus of the next section. However, the selection of units (whether all the target population defined can be reached - census - or a sampling design will be applied) should consider carefully the availability of a sampling frame. If it is not possible to identify and locate farms/herds/flocks, a surveillance designer should consider where else animals can be located and sampled.\\ \\ | ||
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| ===== 7.3 Target unit level ===== | ===== 7.3 Target unit level ===== | ||
| \\ The target unit is the level of the population for which __conclusions will be drawn__ (for instance animal or herds).\\ \\ Before sampling a population, a target unit should be define which is the unit of interest when reporting results and drawing conclusions. Target units may be either groups or individuals, and the choice will depend on the aim of the surveillance component. For instance, the target unit will be “herd” if one wants to detect infected herds, estimate the prevalence of infected herds in a region or be able to declare all herds in a given area free from disease. It will be “animals” if one wants for instance to detect cases of disease, estimate the prevalence of a disease in a given animal population or declare a wild population free from disease.\\ \\ {{:files:risksur.jpg?nolink&50 |}}__**Framework details**__: The following options are considered the RISKSUR design framework (drop-down list)\\ | \\ The target unit is the level of the population for which __conclusions will be drawn__ (for instance animal or herds).\\ \\ Before sampling a population, a target unit should be define which is the unit of interest when reporting results and drawing conclusions. Target units may be either groups or individuals, and the choice will depend on the aim of the surveillance component. For instance, the target unit will be “herd” if one wants to detect infected herds, estimate the prevalence of infected herds in a region or be able to declare all herds in a given area free from disease. It will be “animals” if one wants for instance to detect cases of disease, estimate the prevalence of a disease in a given animal population or declare a wild population free from disease.\\ \\ {{:files:risksur.jpg?nolink&50 |}}__**Framework details**__: The following options are considered the RISKSUR design framework (drop-down list)\\ | ||
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| * Other | * Other | ||
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| ===== 7.4 Sampling unit - individual or group ===== | ===== 7.4 Sampling unit - individual or group ===== | ||
| \\ Sampling units are the units that will actually be sampled.\\ \\ a) INDIVIDUALS: Individual animal samples\\ \\ b) MULTIPLE GROUP SAMPLE: Collective/pooled samples which represent multiple animals, but not the entire target unit referred to above (for instance you will take one sample per pen, but target units are expected to be composed of multiple pens; bulk milk samples for more than one group of cows per herd, etc)\\ \\ c) 1 SAMPLE PER GROUP: Collective/pooled samples which represent the entire group referred to in your target unit (for instance, if your target unit is a pen, and you will take one environmental sample per pen; or one bulk milk sample per herd).\\ \\ | \\ Sampling units are the units that will actually be sampled.\\ \\ a) INDIVIDUALS: Individual animal samples\\ \\ b) MULTIPLE GROUP SAMPLE: Collective/pooled samples which represent multiple animals, but not the entire target unit referred to above (for instance you will take one sample per pen, but target units are expected to be composed of multiple pens; bulk milk samples for more than one group of cows per herd, etc)\\ \\ c) 1 SAMPLE PER GROUP: Collective/pooled samples which represent the entire group referred to in your target unit (for instance, if your target unit is a pen, and you will take one environmental sample per pen; or one bulk milk sample per herd).\\ \\ | ||
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| ===== 7.5 Sampling design ===== | ===== 7.5 Sampling design ===== | ||
| \\ Based on the decisions outlined above, a surveillance designer should determine whether one or two (or multi-) -stage sampling will be employed:\\ \\ | \\ Based on the decisions outlined above, a surveillance designer should determine whether one or two (or multi-) -stage sampling will be employed:\\ \\ | ||