Statistics How To

Types of Variable > Qualitative variable What is a qualitative variable? Watch the video for an overview of qualitative variables, or read on below. Can’t see the video? Click here to watch it on YouTube. A qualitative variable, also called a categorical variable, is a variable that isn’t numerical. It describes data that fits into … Read more

Probability Distributions > Beta Geometric Distribution What is the Beta Geometric Distribution? The beta geometric distribution (also called the Type I Geometric) is a compound distribution that is a generalization of the geometric distribution. While the geometric distribution models the number of failures that will occur before the first observed success in a sequence of … Read more

Survival Analysis > Hazard Function What is a Hazard Function?   The hazard function (also called the force of mortality, instantaneous failure rate, instantaneous death rate, or age-specific failure rate) is a way to model data distribution in survival analysis. The most common use of the function is to model a participant’s chance of death … Read more

Probability Distributions > Stable Distribution What is a Stable Distribution? Stable distributions are a family of probability distributions that share certain properties. They were first described by Paul Lévy in 1925 [1] and so are also sometimes called Lévy alpha-stable distributions. A random variable is stable if you take two independent copies of a random … Read more

Probability Distributions > Triangular Distribution Contents: The median is the value that divides the sample data into two equal halves: one of the right and one on the left. The mean is the average of the sample data. You’ll want to avoid outliers because it can skew the parameter estimates. For example, one tiny outlier … Read more

Probability Distributions > Truncated Distribution What is a truncated distribution? A truncated distribution has its domain (the x-values) restricted to a certain range of values. For example, you might restrict your x-values to between 0 and 100, written in math terminology as {0 > x > 100}. There are several types of truncated distributions: Truncated … Read more

List of probability distributions > bimodal distribution Bimodal Distribution: Two Peaks. A bimodal distribution has two modes (peaks) that may or may not be symmetric .       Most probability distributions have one peak, which happens around the mean or median [2]. For example, a bell curve typically shows concentration of observations, typically around … Read more

Probability and Statistics > Probability > Mutually Exclusive Events What is a Mutually Exclusive Event? Mutually exclusive events, in a single experiment, can’t happen at the same time. They are sometimes called disjoint events [1]. For example, you can’t pass a test and fail it at the same time. In other words, the events “passing … Read more

Descriptive Statistics > Run Chart What is a run chart? A run chart, also called a run-sequence plot, is a type of line graph that displays observed data in a time sequence. It can help detect changes in data, or anomalies, over time. Run charts have many applications in medical research, as well as in … Read more

Probability Distributions > What is a Bivariate Distribution? A bivariate distribution (or bivariate probability distribution) is a joint distribution with two variables of interest. The bivariate distribution gives probabilities for simultaneous outcomes of the two random variables. A discrete joint distribution has at most a countable number of possible outcomes (basically, “countable” means you can … Read more