Error Propagation

All physical quantities that are measured have some uncertainty (error) associated to them. Error propagation (or Propagation of Uncertainty) refers to the fact that whenever you use measurements (with some error) to calculate new...

Instrumental Variables

Instrumental variables in statistics are variables that we use during linear regression analysis to account for the presence of correlation between two variables in our regression model. They are also used to deal with...

Degrees of Freedom

Degrees of freedom in statistics means the number of independent values that can be varied without changing a given parameter value. Let us understand this by means of an example. Suppose you are given 5...

Confounding variables

Whenever we carry out a statistical experiment there are two kinds of variables- dependent and independent variables. We wish to quantify the effect that the independent variable has on the dependent variable. For this,...

Reliability Theory

Reliability Theory is a branch of statistics that deals with the study of determining probabilities of failure of objects and systems comprising of a number of components. The reliability of the system of course...

Queuing Theory and Queuing Models

Queuing theory is the study of processes which involve waiting in line (queue) for a service. It consists of the development of mathematical models which mimic a real life situation and the application of...

Z score to Percentile

Before we understand how to convert z score to percentile we should understand what the terms z score and percentile mean. In the standard normal distribution the value taken by the variable is called the...

Content Validity

Suppose we want to test some property of a particular construct. Then we must design a test or a metric which measures the property. For example to study the intelligence of a person we...