KEY FEATURES: Introduces students to developing research questions and shows their importance in driving research design. Rarely taught topics, such as how to enter and clean data, offer students information missed in both research methods and statistics courses. Shows how to write up survey results for academic, business and nonprofit reports to alleviate the confusion students feel about how to write up findings. Rigorous treatment of sampling focuses on many sampling issues from probability theory to weighting. Offers the process of actually conducting a survey with advice on administering surveys, incentives, and improving response rates.

What Is the Central Limit Theorem?

Erin Ruel

The Central Limit Theorem states that as the sample size n approaches infinity, the mean of the sampling distribution (presented in Q21) approaches the normal bell-shaped distribution. This theorem is telling us that the size of the sample is very important. The larger the sample size, the better the sampling distribution will be and the more closely the sample mean for some variable will reflect the population mean for that variable. In other words, the larger the sample size, the narrower the bell curve will be, and the smaller the sample size, the wider the bell curve will be.

The general rule of thumb is that we need a sample of at least size n = 200 to ...

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