Statistics How To

Contingency Tables > Expected Frequency What is Expected Frequency? The expected frequency is a probability count that appears in contingency table calculations including the chi-square test. Expected frequencies also used to calculate standardized residuals, where the expected count is subtracted from the observed count in the numerator. Observed Frequencies are counts made from experimental data. … Read more

Design of Experiments > Placebo Effect What is the Placebo Effect? The placebo effect is when a medical intervention results in a positive outcome. It results from the person’s anticipation that the pill or potion will be beneficial, rather than any property of the drug itself. In other words, patients who are more optimistic about … Read more

Probability > Conditional Relative Frequency You might find it helpful to read this article first: What is a two way table? What is Conditional Relative Frequency? In a contingency table (sometimes called a two way frequency table or crosstabs), conditional relative frequency is it’s a fraction that tells you how many members of of a … Read more

Statistics Definitions > Cohort Study A Cohort study, used in the medical fields and social sciences, is an observational study used to estimate how often disease or life events happen in a certain population. “Life events” might include: incidence rate, relative risk or absolute risk. A cohort is a defined group, like “nurses,” “10-19 year-olds,” … Read more

RCTs > Relative Risk and Absolute Risk Contents: Relative Risk Relative Risk Reduction Absolute Risk Absolute Risk Reduction Need help with a homework problem? Check out our tutoring page! 1. What is Relative Risk? The relative risk (also called the risk ratio) of something happening is where you compare the odds for two groups against … Read more

Statistics Definitions > False Positive and False Negative What is a False Positive? A false positive is where you receive a positive result for a test, when you should have received a negative results. It’s sometimes called a “false alarm” or “false positive error.” It’s usually used in the medical field, but it can also … Read more

Probability and Statistics Index > Regression Analysis > Line of best fit What is the Line of Best Fit? The line of best fit (or trendline) is an educated guess about where a linear equation might fall in a set of data plotted on a scatter plot. Trend lines are usually plotted with software, as … Read more

Statistics Definitions > Unbiased You may want to read about bias first: What is bias? Contents: Overview Unbiased estimators MVUEs What does it mean to be Unbiased in Statistics? Watch the video for an overview on being unbiased, or read on below. Can’t see the video? Click here to watch it on YouTube. In daily … Read more

Probability and Statistics Index > Regression Analysis > Validity Coefficient You may find it useful to read about validity first. See: Internal validity Construct Validity Validity Coefficient: Definition Validity tells you how useful your experimental results are; a validity coefficient is a gauge of how strong (or weak) that “usefulness” factor is. For example, let’s … Read more

Homoscedasticity > What is the Brown-Forsythe Test? The Brown-Forsythe (B-F) Test is for testing the assumption of equal variances in ANOVA. It is a modification of the Levene Test. How the Test Works Both the Levene and B-F tests transform dependent variables for use in an ANOVA test. The only difference between the two tests … Read more