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the use of a power target, i.e. the power of statistical test to be applied once the sample is collected. using a confidence level, i.e. the larger the required confidence level, the larger the sample size (given a constant precision requirement).
An example of the relationship between sample size and power levels. Higher power requires larger sample sizes. Statistical power may depend on a number of factors. Some factors may be particular to a specific testing situation, but in normal use, power depends on the following three aspects that can be potentially controlled by the practitioner:
G*Power has a built-in tool for determining effect size if it cannot be estimated from prior literature or is not easily calculable. The table lists all possible analyses that the updated G*Power 3.1 can perform for various functions. A priori analyses are one of the most commonly used analyses in research and calculate the needed sample size ...
Matched or independent study designs may be used. Power, sample size, and the detectable alternative hypothesis are interrelated. The user specifies any two of these three quantities and the program derives the third. A description of each calculation, written in English, is generated and may be copied into the user's documents.
It is one of a class of exact tests, so called because the significance of the deviation from a null hypothesis (e.g., p-value) can be calculated exactly, rather than relying on an approximation that becomes exact in the limit as the sample size grows to infinity, as with many statistical tests.
Steps for using sample size tables: Postulate the effect size of interest, α, and β. Check sample size table [20] Select the table corresponding to the selected α; Locate the row corresponding to the desired power; Locate the column corresponding to the estimated effect size. The intersection of the column and row is the minimum sample size ...
McDonald recommends to always use an exact test (exact test of goodness-of-fit, Fisher's exact test) if the total sample size is less than 1 000 . There is nothing magical about a sample size of 1 000, it's just a nice round number that is well within the range where an exact test, chi-square test, and G –test will give almost identical p values.
The simplest bootstrap method involves taking the original data set of heights, and, using a computer, sampling from it to form a new sample (called a 'resample' or bootstrap sample) that is also of size N. The bootstrap sample is taken from the original by using sampling with replacement (e.g. we might 'resample' 5 times from [1,2,3,4,5] and ...