Difference between revisions of "Sampling strategies"
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| − | The information gained through the study of disease in populations which will be increased if more members of the population are sampled. However, | + | The information gained through the study of disease in populations which will be increased if more members of the population are sampled. However, the sampling of every individual in a population is rarely feasible from either a logistical or an economic perspective (except in the case of very small-scale studies). '''Censuses''' are a form of descriptive study which aims to systematically collect information about every member of the population of interest (the ''source population''), and are carried out in many countries for both livestock as well as for humans (although information regarding disease may not be collected). '''Statistical surveys''' are another type of descriptive study, which aim to select a sample (known as the '''study sample''') from the source population, with the intention of extrapolating the information about these individuals to the source population. Similarly, in most analytic studies, a sample of the population must be selected for the same reasons.<br> |
This process of sampling from populations poses potential problems, as it must both select a sufficient number of individuals in order to be useful for the purposes of the study (whilst not sampling more than is required), and must also ensure that any biases in the selection process are minimised. | This process of sampling from populations poses potential problems, as it must both select a sufficient number of individuals in order to be useful for the purposes of the study (whilst not sampling more than is required), and must also ensure that any biases in the selection process are minimised. | ||
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==Terminology== | ==Terminology== | ||
| + | A number of concepts relating to | ||
| − | == | + | ===Target population=== |
| + | The target population is the population to which the results of the study may be extrapolated out to, even if not all members of this population were eligible for sampling | ||
| − | == | + | ===Source population=== |
| + | The source population is the population from which the sample was taken | ||
| + | ===Study sample=== | ||
| + | The sample population | ||
| + | |||
| + | ===Probability sampling=== | ||
| + | |||
| + | ===Non-probability sampling=== | ||
| + | |||
| + | ==Sample size calculation== | ||
[[Category:Veterinary Epidemiology - Introduction|E]] | [[Category:Veterinary Epidemiology - Introduction|E]] | ||
Revision as of 14:45, 9 December 2010
The information gained through the study of disease in populations which will be increased if more members of the population are sampled. However, the sampling of every individual in a population is rarely feasible from either a logistical or an economic perspective (except in the case of very small-scale studies). Censuses are a form of descriptive study which aims to systematically collect information about every member of the population of interest (the source population), and are carried out in many countries for both livestock as well as for humans (although information regarding disease may not be collected). Statistical surveys are another type of descriptive study, which aim to select a sample (known as the study sample) from the source population, with the intention of extrapolating the information about these individuals to the source population. Similarly, in most analytic studies, a sample of the population must be selected for the same reasons.
This process of sampling from populations poses potential problems, as it must both select a sufficient number of individuals in order to be useful for the purposes of the study (whilst not sampling more than is required), and must also ensure that any biases in the selection process are minimised.
Terminology
A number of concepts relating to
Target population
The target population is the population to which the results of the study may be extrapolated out to, even if not all members of this population were eligible for sampling
Source population
The source population is the population from which the sample was taken
Study sample
The sample population