Key formulas
From the Sampling & CLT formula sheet
- Standard Error of xbar:
SE_xbar = sigma / sqrt(n)— Standard deviation of the sampling distribution of the sample mean.
Module 4 · Sampling & CLT · Topic 2
Sampling Methods
Simple Random Sample (SRS). Every possible sample of size n has an equal chance of being selected. This is the gold standard of sampling methods.
Other Probability Methods. Stratified: divide the population into homogeneous strata, then SRS within each stratum. Cluster: divide into clusters, randomly select entire clusters. Systematic: select every kth individual from a list.
Non-Probability Methods. Convenience sampling (whoever is available), voluntary response (self-selected), and quota sampling are non-probability methods. They are prone to bias and generally cannot support statistical inference.
When to use it
Bias Awareness
Sampling bias: sample is not representative. Response bias: respondents give inaccurate answers. Non-response bias: certain groups don’t respond. Good study design minimizes all three.
Related glossary terms
- Parameter: A number that describes an entire population. Example: The true mean height of all students at a university.
- Statistic: A number computed from a sample. Example: The mean height of 80 sampled students.
- Standard Error: The standard deviation of a statistic across repeated samples. Example: The standard error of xbar is sigma divided by sqrt(n).
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