Section 1
The Histogram
By Boundless
![Thumbnail](../../../../../../figures.boundless-cdn.com/17978/square/eference-by-age-and-gender.jpg)
Cross tabulation (or crosstabs for short) is a statistical process that summarizes categorical data to create a contingency table.
![Thumbnail](../../../../../../figures.boundless-cdn.com/17960/square/ch2-hist-1.jpg)
To draw a histogram, one must decide how many intervals represent the data, the width of the intervals, and the starting point for the first interval.
![Thumbnail](../../../../../../figures.boundless-cdn.com/17959/raw/lack-cherry-tree-histogram.jpg)
A histogram is a graphical representation of the distribution of data.
![Thumbnail](../../../../../../figures.boundless-cdn.com/17961/square/on-of-1d-histogram-and-kde.jpg)
Density estimation is the construction of an estimate based on observed data of an unobservable, underlying probability density function.
![Thumbnail](../../../../../../figures.boundless-cdn.com/18394/square/penelement-fieldelemformat-gif.gif)
A variable is any characteristic, number, or quantity that can be measured or counted.
![Thumbnail](../../../../../../figures.boundless-cdn.com/17977/square/3464814231-72beee0bb9.jpeg)
Controlling for a variable is a method to reduce the effect of extraneous variations that may also affect the value of the dependent variable.
![Thumbnail](../../../../../../figures.boundless-cdn.com/17981/square/j.r.microscop.soc.1887p193.jpg)
Selective breeding is a field concerned with testing hypotheses and theories of evolution by using controlled experiments.