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Introduction to Statistical Control Today, manufacturing companies face increasing competition due to raw material cost and other factors like employees and resources. Therefore companies must concentrate on strategies to improve their level to come best in the market. Companies must try for continuous improvement in quality, efficiency and cost reduction. Many companies still rely on inspection after production for quality analysis. In recent trends, many control methods has come into existence which would increase the product quality. Control plays a major part in every industry for the betterment of the process and the quality. For this purpose, statistical approach is used in many organizations. In statistics, controlling a variable attempts to reduce the effect of other variables i.e., it is an observational study effect of one variable is measured while all other variables are kept constant.For statistical control in research , during experiments, researchers assign varia...

Selection Bias occurs when the data selected as a sample is not random enough. In other words, the sample is not a true one and not representative of the population that we wish to study. The result obtained from a sample that suffers selection bias does not reflect the correct conclusion. The presence of selection bias results in false results. Therefore, if it is not corrected the conclusions drawn from the study will not be precise. Selection bias have adverse impact on surveys and epidemiological studies. Examples of Selection Bias There are many cases where selection bias can occur. When a particular section of the population is ignored (due to various reasons such as inconvenience in collection of data) in the sample selected from the population, selection bias will occur. What is Attrition Bias? It is a type of selection bias that occurs when a particular group or section of the population does not participate or withdraws participants from the survey. An example of a...

Introduction of Sample Size Population in statistics means the collection of a set of all the elements required for a particular study. Sample is a subset of that entire set chosen very carefully. It is a very important base of statistical analysis. Very often we come across situations in which we may not be able to study the entire population. In that cases we have to draw well representative samples from the population and infer about the unknown characteristics of the population solely on the basis of that sample. Inference is one of the most important task of statistics and drawing a valid sample is the first and foremost part of inferring. Definition of Sample Size Sample size in Statistics is defined as the number of elements that we wish to include in a sample. Importance of Sample Size Selection of size of a sample is a very crucial work. One of the pivotal activity of designing a sample survey is to decide the proper sample size. Esti...