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diet for renal failure

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diet for renal failure

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  1. SURVEY Submitted toSubmitted by Dr. A.VIJAY KUMAR Ph.DJ.SRAVAN KUMAR Assistant professor KV/13-040 Dept of veterinary public health & epidemiology

  2. SURVEYS • A survey is an examination of an aggregate of units • A group of animals is an example of an aggregate. • Survey can be undertaken on a sample of the population less commonly a census,which examines the total animal population ,can be undertaken • A longitudinal survey records events over a period of time.

  3. A particular type of diagnostic survey is ‘screening’. • This is the identification of undiagnosed cases of disease using rapid tests or examinations. • Screening frequently involves investigation of the total population ‘mass screening’. • Prescriptive screening aims at early identification of diseases that can be controlled better if they are detected early in their pathogenesiss.

  4. Informmation on disease and associated events ,such as productivity ,can be obtained from survey • This involve counting members of an aggregate of units and measuring their characteristics. • An important application of surveys in epidemiology is estimation of the prevalence of clinical disease,infection ,or seropositive animals from samples of an animal population

  5. A survey of prevalence can involve • A single sample,either to determine prevalence or to determine whether or not disease is present in group of animals • Two samples to compare prevalence • 3 or more samples

  6. Censuses and sample surveys • If all animals in a population are investigated,the survey is a census • Demographic censuses of human and animal populations are conduced regularly in many countries to determine the size and structure of the populations.

  7. Types of sampling 1)Non probability sampling:in which the choice of the sample is left to the investigator 2)probability sampling :in which the selection of the sample is made using a deliberate,unbiased,process ,so that each sampling unit in a group has an equal probability of being selected; this is the basis of random sampling.S

  8. Non probability sampling methods Convenience sampling: • Convenience sampling is the collection of easily accessible sampling units. • When convenience is the main criterion for selecting a sample,it is very unlikely that the sample will be truly representative of the study population ,resulting in biased estimates.

  9. Purposive selection • Purposive selection is the choice of a sample , the averages of whose quantitative characteristics or distribution of whose qualitative characteristics are similar to those of the target population. • The object is to select a sample where characteristics are balanced with those of the target population.

  10. Probability sampling methods • A simple random sample: it is selected by drawing up a list of all animals or other relevent sampling units in the study population,and then selecting the sampling units randomly . • Systematic sampling: systematic sampling involves selection of sampling units at equal intervals , the first animal being selected randomly.

  11. Simple random versus systematic sampling: • A systematic sample does not require knowlegdge of the total size of the study population • A simple random sample ,however,can only be selected when all of the animals in the study population are identified. • However, if lists are not available ,it may be difficult –even impossible- to draw up the sampling frame and therefore to select the random sample.

  12. Stratified sampling: • A stratified random sample is obtained by dividing the study population into exclusive groups, then randomly sampling units from all of the individual strata. • Stratification can improve the accuracy of a sample because it overcomes the tendency of a simple random sample to either over-represent or under-represent some sections of the sampling frame.

  13. Cluster sampling:strata are defined by geographical loactions ,such as different countries,shires,parishes and villages ,or by other categories such as veterinary practices or periods of time during which samples are selected. • The strata are then termed clusters. • Sampling from all of these clusters can be time –consuming and costly • This disadvantage can be overcome by selecting a few clusters,and sampling the animals only in these clusters;for example ,animals in few villagges or herds could be sampled . • This is cluster sampling.

  14. All animals in each selected cluster are sampled ; this is one-stage cluster sampling. • A sample also may be selected in more than one stage • Thus a sample of clusters can be selected,followed by sub sampling of some animals in the clusters • This procedure is therefore called two stage cluster sampling • The clusters are the primary units,and the selected members of the sub –samples are the secondary units.

  15. For example: • Sampling regions ,then dairy farms in each selected region, then cows on each selected farm • This is multistage cluster sampling • The sampling technique at each stage is usually simple random sampling.

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