# Statistics Help and Tutorials by Topic

What Is Correlation?
One goal of statistics is to find patterns hiding in data. Correlation is a tool that does just that. Find out how this is done.

An Introduction to Hypothesis Testing
Inferential statistics is used to test the validity of a hypothesis. This process can seem technical, however it relies upon intuitive ideas from probability. Read a story to see how hypothesis testing works.

Correlation and Causation in Statistics
It's relatively easy to show that two variables are statistically correlated. What's hard to do is to show that if two things are correlated then one is causing the other to occur. Read on to see how ice cream, drowning, and thymus glands relate to correlation and causation.

An Introduction to the Bell Curve
Bell curve appear throughout the study of statistics. What are they? Discover what a bell curve is, and some of the surprising places that they show up in real life.

What Is the Standard Bell Curve?
There are an infinite number of possible bell curves. To simplify matters greatly, we consider one standard bell curve. We are then able to use this standard bell curve to answer questions pertaining to the other bell curves.

How to Calculate a Standard Deviation
See step by step instructions on what your calculator does when you ask it to calculate a standard deviation.

How to Make a Boxplot
Boxplots, or box and whisker plots, assemble the range, median and quartiles of a data set. Two or more sets of data can be compared by looking at the boxes and whiskers of the graph.

How to Make a Stem Plot
Stem and leaf plots are a useful way to organize data while retaining all of the data values.

Common Statistics Mistakes
Be careful not to make these mistakes when you're doing statistics.

How to Calculate Probabilities with A Standard Normal Distribution Table
Although programs exist to calculate the probability that a variable lies between two z scores, using a table to compute these probabilities is a worthwhile exercise.

Levels of Measurement
Data comes in many different forms, and measures a variety of things. The four levels of measurement, help to identify what we obtain data about.

7 Common Graphs in Statistics
Graphs help us to display our data. Find out more about seven of the most common graphs in statistics.

Ways to Find the Average
The average or center of a data set is an important area of descriptive statistics. The mean, median, mode and midrange are measure the center of the data.

What Is Statistics?
This is an introduction to many of the ideas found in statistics.

What Is Statistical Sampling?
Statistics approaches large problems by sampling, a technique in which only some of the population are studied. Data about the sample allow us to reach conclusions about the population.

What Is the Median?
The median is one of the three main ways to find the average or center of a data set.

What Are Pie Charts?
To graph qualitative data, one helpful way to depict it is to make a pie chart.

How to Conduct a Hypothesis Test
Hypothesis testing is one of the main topics of inferential statistics. Find out how to tell the likelihood of an observed event occurring randomly.

What Is a Bar Graph
A bar graph is used when you have qualitative data. Find out how to construct a bar graph from a set of data.

What Is a Histogram?
A common graph in statistics is called a histogram. Histograms look very much like bar graphs, but there are several key differences.

Simpson's paradox, also known as the simpson-yule effect, is an unexpected result that occurs when data is grouped together. A correlation or relationship for all of several groups can be reversed when the data is aggregated.

The Number e: 2.7182818284590452...
The mathematical constant e is found throughout mathematics, including probability and statistics. This number has many important properties.

Histogram Classes
One feature of a histogram are the classes or bins that split up the horizontal line on the bottom. Find out how to know how many classes there should be and how wide they should be.

Differences Between a Tally and a Count
In statistics a tally system is sometimes used to organize data. See how this is done and how a tally differs from a count.

Simple Random Samples from a Table of Random Digits
Simple random samples are important in statistics because they eliminate sampling bias and allow us to use theorems from probability. To obtain a simple random sample we can use a table of random digits.

Discuss in my forum