# Estimation Principles

• ### Confidence Intervals

This resource assists the user in reading, constructing, and understanding confidence intervals.
• ### Stats: Sample Size Determination

This resource provides the user with a formula for obtaining sample sizes of a mean and proportion.
• ### P Values and Statistical Significance

This resource defines what a p-value is, why .05 is significant, and when to use it. It also covers related topics such as one-tailed/two-tailed tests and hypothesis testing.
• ### Strategies for data analysis

This presentation on data analysis addresses observational studies and randomized controlled trials in two different sections. Types of studies are defined and examples of each study is given to emphasize the differences. Factors and variables are also discussed.

• ### New Confidence Interval Applet

This simulation applet shows groups of confidence intervals for a given alpha based on a standard normal distribution. It shows how changes in alpha affect the proportion of confidence intervals that contain the mean. An article and an alternative source for this applet can be found at http://www.amstat.org/publications/jse/v6n3/applets/confidenceinterval.html.
• ### Introductory Statistics: Concepts, Models, and Applications

This goal of this resource is to aid in the understanding of the relationship between statistics and the scientific method and how it applies to psychology and the behavioral sciences. The learner will learn how to read and understand the statistics presented in the professional literature and will learn how to calculate and communicate statistical information to others.
• ### HyperStat Online Textbook

This resource contains a broad range of information concerning statistics. It is divided up into 18 chapters and also includes links to other resources pertaining to statistics.
• ### 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.

• ### Standard Deviation

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