What is a Histogram: Its types and how to create one

What is a histogram, do you know? Also known as the "Frequency Dispersion Diagram", it is one of the tools that make up the quality!

It is basically a graphical representation, in columns (rectangles), of a set of data previously tabulated and divided into even classes.

You may ask me, "What then is the basis and height of these rectangles? ". Well, the basis of each column represents a class. Thus we can identify which class is the function of each rectangle.

The height of these columns represents the amount or frequency with which the value of this class occurred in the data set.

This tool provides a way to evaluate the distribution of the data and allows to verify the behavior of a process in relation to its specification.

In the title of this article, I said I would show the types of histograms, and 6 are the main ones. So now that you've learned what a histogram is, I'll talk about them, their shapes, and what do they mean. Prepared?

What are these 6 types of histograms?

1 - Symmetric

This first type is also called "normal distribution". It has a higher frequency in the center and decreases according to the approximation of the edges, both the right and the left.

The stable and standardized processes are represented by this histogram.

2 - Asymmetrical

As can be seen from the image, it is asymmetrical when it has only one peak.

But what does it represent? It usually shows a situation where it has only one specification limit and is controlled throughout the process.

3 - Cliff

As the name itself says, it is as if it were to fall. Itlooks like a gully.

It occurs when the data is deleted, thereby causing a cut in the figure, giving a slight impression that the histogram is incomplete.

4 - Two peaks

As the image shows, it is characterized by having two frequencies higher than the others.

It always occurs when there is a mix of different data, e.g. when data is collected under very different conditions, either with the operator, equipment or raw material.

5 - Flattened

You may have heard of this type of histogram under a different name. It is also known as "plateau".

In this type, the frequencies are very close to each other, at fairly equivalent levels. This occurs when there are mixtures of distributions with different averages.

6 - Isolated island

This is the last type of histogram. It makes it very clear that there are two processes, or two problems that are well isolated in relation to the cause.

There is a space between the histograms, this shows that there was some abnormality due to a fault.

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Step by step how to create a histogram

STEP 1: Sample determination.

The sample must be as random as possible so that it can represent the totality.

In order for you to have a reliable and representative sample, you need to have 50 to 100 experimentations.

STEP 2: Calculating the Amplitude

The first thing you have to do in this step is to identify the largest and smallest value of the sample.

Thus, the amplitude (R) is the difference between these values.

R = highest value - lowest value

STEP 3: determine the number of classes

You need to choose the number of classes to be used in the histogram. The number of classes is proportional to the size of the demand.

There’s no right number, but it can't be too small, not to de-characterize the histogram, and not too large, to spread the data too much.

STEP 4: class interval calculation

Yes, more calculation for you to do. But it is very simple:

H = R / K

But what do these letters mean?

H = range of classes

R = amplitude

K = number of classes

STEP 5: calculation of the extremes of the classes

And there come more calculations... To perform this calculation it is necessary that you select the lowest value of the sample, so you can have a lower level of the first class.

Now, to determine the upper limit (LS) of the first class, simply add the value of the range of classes (H) with the lower limit (LI):

LS = LI + H

The other limits are calculated according to the limits of the first class.

STEP 6: assemble the histogram

At last, we come to the end, it’s time to assemble this tool. For this to occur, you need to count the number of elements in each class, and with that, have all the data needed to assemble the histogram.

Good collection + good histogram + correct analysis = positive results for the company

Throughout this article, you learned what a histogram is, how to put one together and you could still realize the importance of it to your company processes.

It is important that you make a good data collection, transfer them to the histogram and make a correct analysis of them, otherwise it won’t work.

Finally, it is necessary to have a lot of attention throughout this process, so that a significant result for the company is achieved.

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