# Sampling & Survey Issues

• ### Probability Sampling

This site describes in detail 5 different types of random sampling, giving examples, definitions, and procedures.
• ### Nonprobability Sampling

This site describes numerous methods of nonprobability sampling, including accidental, haphazard or convenience sampling and the many types of purposive methods.

• ### Survey Design

This site takes the user through the steps and decisions necessary when designing a survey. Pros and cons for each method are outlined and other issues in survey design are presented.
• ### Confidence Intervals for Means Applet

This applet simulates finding confidence intervals for the mean of a normal random variable. A sample of size 20 is generated from a standard normal random variable. The blue marks represent the sample data. The sample mean X and sample standard deviation s are found and used to calculate the confidence interval. The black intervals are the confidence intervals which include the true mean 0, and the red intervals are those which exclude 0. This applet needs to be resized for optimal viewing.
• ### Sample Size Calculator

Use the Sample Size Calculator to determine the sample size you need in order to get results that reflect the target population as precisely as needed. You can also find the level of precision you have in an existing sample. The site also describes terms you need to know to understand confidence intervals and what they mean.

• ### Poem: Statistics

Statistics is a poem by Canadian physician Neil Harding McAlister (1952 - ). The poem contains material that can help with class discussions about sample surveys, medical experiments, and significance testing.
• ### Standard Deviation

This resource defines and explains standard deviation and the normal distribution.