Categories: Quantitative Analysis

Grubbs outlier test in Quantitative Analysis & Research

 

What is an Outlier?

Any observation that is not within the normal trend is known as an outlier. Outlier can most of the time occur due to human error. Following is a table which provides the data for number of children in a country “A”:

 

 

The above data in Red clearly shows that these are outlier within the normal trend as it is humanly not possible to have so many children. Therefore in order to check the significance of a data which seems to be an outlier, a Grubbs test is used.

 

Grubbs outlier test:

To test the seemingly out of trend / outlier data that they are significant or not. Through this test we can easily identify that an outlier is really an outlier or not. Grubbs test calculates “Z” value of the observation and then decides whether the observation or data is significantly an outlier or not.

 

Cut of point of Z-Value = 4.14

 

Related Post

Z < 4.14 means insignificant (which means the data is not an outlier)
Z > 4.14 means significant (which means the data is an outlier)

 

You can easily check the significance of an outlier through Grubbs test by using any online available tool. One of the website that I have used mostly in my statistical analysis to test an outlier through Grubbs test is as follow:

http://graphpad.com/quickcalcs/Grubbs1.cfm

 

Suppose Grubbs test identifies certain data is being significantly out of trend, then what should be done next in order to achieve accurate results. Here we have three options:

 

  1. Remove the outlier from the population, but this creates biasness. Therefore, we should avoid this option, in order to make out observations unbiased.
  2. Transform your observation. For example take a log transformation of your data will reduce the error percentage.
  3. Increase the sample size so that your output tends toward actual result.

 

Click here to read more.




  • Mikel

    View Comments

    • @Mikel I have gone through most of your technical posts and notice there are no comments from the site. Could you tell me if you get views from outside. You should as these are highly informative blogs.

    Recent Posts

    Heart Attack Causes and its Solution

    What is the Main Cause of a Heart Attack? What is its Solution? A heart attack is the blockage of… Read More

    11 months ago

    Understanding the Debt Ceiling: Its Impact, Importance, and Implications

    In the vast economic arena, one term that often takes center stage, inciting extensive debates and discussions, is the "debt… Read More

    1 year ago

    De-Dollarization: The New World Order of Currency and Its Global Impact

    De-Dollarization: The Changing Face of Global Finance The financial landscape is in a state of flux, with an intriguing economic… Read More

    1 year ago

    Unstoppable Bayern Munich: The Story Behind Their 11th Consecutive Bundesliga Title

    The curtains closed on a dramatic Bundesliga season with Bayern Munich standing tall once again, clinching their 11th straight title.… Read More

    1 year ago

    Celine Dion Cancels Concert Tour Due to Deteriorating Stiff-Person Syndrome

    The Unfolding Story of Celine Dion's Health In recent news that has left fans across the globe stunned, iconic singer… Read More

    1 year ago

    Navigating the Crossroads: LeBron James, Anthony Davis, and the LA Lakers’ Uncertain Future

    As the echoes of the recent NBA season start to fade, the attention of enthusiasts is firmly glued to one… Read More

    1 year ago