Population and Sample

Statisticians carry on endlessly about two particular terms - population and sample . There is in fact good reason for the emphasis placed on these concepts and we need to be clear about the distinction. 

One of the hall-marks of good research is that there should be a clear definition of the target group of individuals (or objects) about whom we are aiming to draw a conclusion. The term population is used to cover all the individuals who fall within 

Essential Statistics for the Pharmaceutical Sciences Philip Rowe 

The complete collection of individuals about whom we wish to draw some conclusion. 

Since it is usually impossible to study a whole population, real science is carried out on smaller samples randomly selected from the larger population. The sample is unlikely to be of any direct interest to the reader. However, it is of indirect interest -the hope is that we can use the sample as a tool to throw light on the nature of the general population. 

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Note that the definition of the correlation coefficient is identical both for samples and populations. 

Random errors Relative standard deviation Robust variance Samples and populations Standard deviation of the mean (standard error of the mean)... 

Application of Sparse Sampling and Population Kinetic Methods... 

Any obtained set of measurements (xi, X2... Xn is defined in statistics as a sample of this continuous range of values. Only all possible measurements (which must be infinite in number to cover the whole range) would generate the real set, which is called population. (The statistical term sample can easily be confused in analytical chemistry with the term sample = specimen, as the term population may also have a different meaning. To avoid this confusion, the statistical terms sample and population will always be italicized.)... 

Interaction between two independent CNR1 variants increases risk for cocaine dependence in European Americans a replication study in family-based sample and population-based sample. Neuropsychopharmacology... 

Indicates population exposures to large particles. Provides some correlation with 24-hour filter sampling and population exposure in places where particulate emission controls are poor. Difficult to relate to health effects. 

Table 5.2 Symbols Used for Small Sample and Population Parameters...

It is dear that the difference between sample and population may become larger, the smaller a sample is. The minimum sample size of N = 30 as specified in standards represents a compromise between the large cost of specimen preparation and accuracy, although it should be noted that for N = 30 the uncertainty remains relatively large. Figure 12.10 shows the confidence intervals which result from the sampling procedure, for the Weibull modulus and the function (the scatter of the... 

Altliough c is based on sampling the entire population, it is sometimes used in forensic and analytical chemistry. One rule of thumb is that if n > 15, population statistics may be used. Simikirly, if aU samples in a population are analyzed, population statistics are appropriate. For example, to determine the average value of coins in a jar full of change, every ccm amid be mcluded in the sampling and population statistics would be appropriate. 

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