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The behavioral sciences to aspire to the highest level of competency by arming them with the tools they need for knowledgeable, informed practice. Essentials of Statistics for the Social and Behavioral Sciencesconcentrates on drawing connections among seemingly disparate statistical procedures and providing intu.
Statistically Figuring Sample SizeWhen designing a study, the sample size is an important consideration because the larger the sample size, the more data you have, and the more precise your results will be (assuming high-quality data). If you know the level of precision you want (that is, your desired margin of error), you can calculate the sample size needed to achieve it.To find the sample size needed to estimate a population mean ( µ), use the following formula:In this formula, MOE represents the desired margin of error (which you set ahead of time), and σ represents the population standard deviation.
If σ is unknown, you can estimate it with the sample standard deviation, s, from a pilot study; z. is the critical value for the confidence level you need. Checking Out Statistical Confidence Interval Critical ValuesCritical values ( z.-values) are an important component of confidence intervals (the statistical technique for estimating population parameters). The z.-value, which appears in the margin of error formula, measures the number of standard errors to be added and subtracted in order to achieve your desired confidence level (the percentage confidence you want). The following table shows common confidence levels and their corresponding z.-values.
Confidence Levelz.– value80%1.2885%1.4490%1.6495%1.9698%2.3399%2.58.