Understand difference beteween both on simple examples from real project. What is the difference? And where is the peak if we talk about right skewed histogram? These and more question are answered in this article.

This article covers

Everything you wanted to know about histogram
Histogram shapes
Histogram skewness
Right skewed histogram (with example)
Left skewed histogram (with example)
Histogram types
Histogram creation in excel
Download histogram excel template

Basics about histogram – normal distribution

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Everything you wanted to know about histogram

Oh, yes, we are again back on statistics., But do not be scared. This one is as simple as run chart, or control chart. Histogram can help you visualize and understand data distribution your process is exiting. So, I suggest to learn and use this basic tool to know when your process need some attention.

How to cr e ate Run chart vs Control chart? (+template) – read here

A histogram is a visual summarization of numerical data showed in specified value ranges.

There are ranges of measured values, also called intervals on X-axis. Y-axis shows occurred times that particular range happened. Both values defines size of bars. Bar width is set by values range. Range width is equal across all X-axis. Each number within particular range is counted in particular range. Counts of numbers within the range defines bars height.

We will need to know Median, Mode, and Mean prior explaining different histogram curve types.

Mean is a arithmetical average of all values.

Median is a middle number of all values.

Mode is the most frequent occurring number.

Relationship between Median, Mode, Mean can help us predict histogram shape.

Mean, Meadian,, Mode – how influencing skewness

RUn chart vs. Control chart – check it out

How to perform Kaizen event? (+template) – read here

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Histogram shapes

Histograms are used to visualize data distribution, and histogram shape can tell you a lot about it.

Normal distribution is a symmetric distribution around mean. Data around mean are more frequent in occurrence in comparison with data far from the mean. Normal distribution appears a bell curve. A normal distribution is the proper term for a probability bell curve. Normal distributions are symmetrical, but not all symmetrical distributions are normal. Mean, mode, and median are one number, or very close together. You can use also control limits to histogram if required. Then you can calculate standard deviation. But this theme will be covered in different video.

Normal data distribution – bell curve ideal distribution

Real data rarely follow normal distribution. Skewness describes differences between values on distribution right, or left side end.

Kurtosis is another parameter describing extreme values on each tale. Both parameters reviews distribution comparing to normal distribution. But, we will focus on skewness.

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Histogram skewness

Skewness measures symmetry of the distribution. Normal distribution has skewness of zero. If skewness is positive value, than we talk about right skewed histogram. If skewness has negative value, than we talk about left skewed histogram.

Skewness is an asymmetry degree in a probability distribution.

People are sometimes confused, bud Skewness does not says about the peak position, but about slopping line.

Improve your processes by using Voice of Customer (+template) – read here

Right skewed histogram

On the right skewed distribution, most of the data values occur on the left side with decreasing data on the right side.

Mean is located on the right side of the curve, mode close to the peak, median located in between. All 3 are not the same number..

Right skewed distribution example:

Machining supervisor wanted to know, what is parts lead time distribution. Together with his team put together data. Majority of parts lead time is 15 days. However there are some with 20 days lead time. Goal is to improve process to get normal distribution around 15 days. This can be a great project goal definition.

Right skewed histogram – right skewed distribution

Formulas to calculate Takt Time/ Cycle time (+template) – read here

Left skewed histogram

On the left skewed distribution, most of the data values occur on the right side.

Mean is located on the left side of the curve, mode close to the peak, median located in between. All 3 are not the same number. It is opposite to right skewed distribution

Left skewed distribution example: