Histograms  Explanation and definition of histograms
What are histograms
Histograms are statistical tools that allow us to quickly and graphically display the distribution of a study, histograms are graphical representations by vertical bars of a frequency distribution of a continuous variable. Each of this bars reflects a range or class, and the height shown is proportional to the frequency (number of times) with the values displayed in each of the intervals.
Histograms will also known by the name "frequency distribution diagrams"
Histograms are used as a tool to help in decision making for the resolution of problems, through the histogram can identify behavioral patterns of all the data and draw conclusions, histograms which allows:
Analysis of data distribution.
Check the degree of compliance with the specifications.
Evaluate the effectiveness of solutions.
Histograms application method
Prior to the explanation of the steps to follow for a histogram, we need to know some preconceptions as:
Range (R) is the value obtained by subtracting the maximum and minimum.
Class (k) is the dimension of the range of variability of the data.
Frequency: number of items within a particular class.
The steps are:

You collect all the data (N) on a datasheet, histograms working with data, often with times, weights, sizes ... and thus obtain the more data the more accurate will be the histogram. The total number of values is called "N".

Get the maximum and minimum values (Vmax.) and (Vmin.).

Set range (R) as follows: R = Vmax.  Vmin, as shown in the formula, we simply subtract the maximum value of the data obtained from the minimum value.
Determine the number of classes (k) we want to exist, this data will determine the bars that want to appear in the histogram.
Calculate the amplitude of each class as follows: i = R / k.
Rounded to the upper integer value if the result is not accurate in terms of the unit.

Set values for the class boundaries.
Build a table of frequency distribution and assign the data to its corresponding class, in doing so we can find the problem that we have values ??on the boundary between one class and another, and do not know which of the two kinds assign, in this If it is recommended to assign these data to one of the two classes, the bottom or the top, but always with the same criteria, so as not to distort the graphic.

Construct histogram shafts, to construct we follow the following criteria, on the horizontal axis the values of the class marks are placed, on the vertical axis the frequency values are placed.
Draw the corresponding boxes, once slots have been determined and know how many measurements fall within each interval, we put the boxes according to the axis of the histogram.
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