Calculating & Graphing Statistical Data

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Why the Statistical Mean and Median of a Histogram Often Have Different Centers

A histogram gives you a rough idea of where the "center" of the data lies. The word center is in quotes because many different statistics are used to designate the center. The two most common measures [more…]

How to Find the Interquartile Range for a Statistical Sample

To obtain a measure of variation based on the five-number summary of a statistical sample, you can find what's called the interquartile range, or IQR.

The purpose of the five-number summary is to give descriptive [more…]

How a Pie Chart Reflects Categorical Data in a Statistical Data Set

A pie chart takes categorical data from a statistical sample and breaks them down by group, showing the percentage of individuals that fall into each group. Because a pie chart takes on the shape of a [more…]

How to Interpret a Statistical Bar Graph

A bar graph (or bar chart) is perhaps the most common statistical data display used by the media. A bar graph breaks categorical data down by group, and represents these amounts by using bars of different [more…]

How Graphs Can Distort Statistics

A statistical graph can give you a false picture of the statistics on which it is based. For example, it can be misleading through its choice of scale on the frequency/relative frequency axis [more…]

How Histograms Show Statistical Data

A histogram is a special graph applied to statistical data broken down into numerically ordered groups; for example, age groups such as 10–20, 21–30, 31–40, and so on. A histogram provides a snapshot of [more…]

How to Group Statistical Data Appropriately in a Histogram

When you create a histogram, it's important to group the data sets into ranges that let you see meaningful patterns in your statistical data. For example, say you want to see if actresses who have won [more…]

How to Place Borderline Statistical Values in a Histogram

When you create a histogram, you need to divide the data set into separate groups. However, some statistical data may be right on the borderline between two groups. What do you do in these situations? [more…]

How to Clearly Label the Axes on a Statistical Histogram

The most complex part of interpreting a statistical histogram is to get a handle on what you want to show on the x and y axes. Having good descriptive labels on the axes will help. Most statistical software [more…]

How Histograms Can Misrepresent Statistical Data

There are no hard and fast rules for how to create a histogram based on a set of statistical data; the person making the graph gets to choose the groupings on the [more…]

Displaying Your Statistical Data with Charts and Graphs

You can summarize your statistical data in a visual way using charts and graphs. These are displays that are organized to give you a big picture of the data in a flash and to zoom in on a particular result [more…]

How to Calculate the Mean of a Statistical Data Set

The most common way to summarize a statistical data set is to describe where the center, or mean, is. One way of thinking about what the center of a data set means is to ask, “What’s a typical value?” [more…]

How to Find the Median Value in a Statistical Data Set

The median is a statistic that is commonly used to measure the center of a data set. However, it is still an unsung hero of statistics in the sense that it isn’t used nearly as often as it should be, although [more…]

How to Identify Skew and Symmetry in a Statistical Histogram

Sometimes the mean versus median debate can get quite interesting. Especially when you look at the skewness and symmetry of your statistical data in a histogram. [more…]

How to Interpret Standard Deviation in a Statistical Data Set

Standard deviation can be difficult to interpret as a single number on its own. Basically, a small standard deviation means that the values in a statistical data set are close to the mean of the data set [more…]

Applying the Empirical Rule (68-95-99.7) to a Statistical Data Set

The Empirical Rule (68-95-99.7) says that if the population of a statistical data set has a normal distribution (where the data are in the shape of a bell curve) with population mean [more…]

How to Calculate Percentiles in Statistics

If all you are interested in is where you stand compared to the rest of the herd, you need a statistic that reports relative standing, and that statistic is called a percentile. The [more…]

How to Gather a Five-Number Summary from a Statistical Sample

If your data create a histogram that is not bell-shaped, you can use a set of statistics that is based on percentiles to describe the big picture of the data. Called the five-number summary, this method [more…]

What a Boxplot Can Tell You about a Statistical Data Set

A boxplot can give you information regarding the shape, variability, and center (or median) of a statistical data set. It is particularly useful for displaying skewed data. [more…]

What a Time Chart Can Tell You about a Statistical Data Set

A time chart (also called a line graph) is a statistical display used to examine trends in data over time (also known as time series data). Time charts show time on the [more…]

How a Time Chart Can Misrepresent Statistical Data

When you create a statistical time chart, you have to evaluate the units of the numbers being plotted. For example, it's misleading to chart the number [more…]

Simplifying Excess Statistical Data in a Time Chart

If a time chart includes too much statistical data, the result can be so complex that it makes it impossible to interpret the data. By reducing the amount of data, it is easier to see patterns emerge from [more…]

How to Calculate Standard Deviation in a Statistical Data Set

By far the most common measure of variation for numerical data in statistics is the standard deviation. The standard deviation measures how concentrated the data are around the mean; the more concentrated [more…]

How to Make a Boxplot from a Five-Number Summary

A boxplot is a one-dimensional graph of numerical data based on the five-number summary. This summary includes the following statistics: the minimum value, the 25th percentile [more…]

How to Spot Statistical Variability in a Histogram

You can get a sense of variability in a statistical data set by looking at its histogram. For example, if the data are all the same, they are all placed into a single bar, and there is no variability. [more…]

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