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30. Essay”Problems arising from the data collection”

The errors manifest themselves during data collection can be divided into two groups · Errors in the sample. They are related to mismatch of the study sample and the general population. · Systematic errors. This group includes all the other errors that are not sampling errors. They result from imperfect or logic concept studies misinterpretation of responses and errors in the processing stage, data analysis and presentation. Systematic errors are divided into two types: · Random. Such errors lead to deviations from the true value to a random value and a random direction. · Accidental. Such errors lead to one-sided deviation of the results from the true value. Systematic errors are more dangerous than the error in the sample: they are more difficult to measure, in addition, an increase in the sample does not always allow them to cut. The amount of bias may exceed ten times the sampling error and turn research results almost nothing. Systematic errors can be reduced. However, such reductions are the tools do not increase the number of samples, and special techniques. To properly applied, it is necessary to identify the main sources of systematic error. There are two main types of systematic error sources of their occurrence: Bug unobserved; Bug surveillance. Unobserved error associated with the inability to obtain data from the elements of the study population. This error can occur for two main reasons: · Part of the object of study is not represented in the sample (non-coverage error); · Elements of the sample did not provide data (non-response error due to lack of on-site or failure of the interview). The error occurs when non-compliance monitoring data on a set of elements presented in the report, the true values. This discrepancy may occur in the following circumstances: · Providing incorrect data elements; · Incorrect registration data;

· Error in the processing, analysis and presentation of research results.

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