1st Quartile and 3rd Quartile

[xxMsJojoxx]

I have a set of numbers: (-18,-14,-12,-8,-7,-6,-4,0,1,2,3,4,5,8,9,14,15)

In R Program, I get the following information.


But with my own calculation, I got 1st quartile as -7.5, and 3rd quartile as 6.5.

What am i doing wrong? Or is there a reason for the discrepancy?

 

[Steven G]

Please show us your work so we can see where you made your mistake.

 

[Dr.Peterson]

I have a set of numbers: (-18,-14,-12,-8,-7,-6,-4,0,1,2,3,4,5,8,9,14,15)

In R Program, I get the following information.
View attachment 23581

But with my own calculation, I got 1st quartile as -7.5, and 3rd quartile as 6.5.

What am i doing wrong? Or is there a reason for the discrepancy?

There are several different definitions of quartiles; you are using a different definition than R uses. I happen to prefer theirs; but if you did what you were taught, then you should do that in class (while being aware that R will often disagree with your results).

For a too-long discussion of this issue (and references to others), see my blog: The Many Meanings of “Quartile”

 

[xxMsJojoxx]

Please show us your work so we can see where you made your mistake.

The median is 1. And the median of the upper range is 6.5 = (5+8)/2, which I got as the 3rd quartile. The median of the lower rannge is -7.5 = (-8+-7)/2, which I got as the 1st quartile.

 

[xxMsJojoxx]

THan

There are several different definitions of quartiles; you are using a different definition than R uses. I happen to prefer theirs; but if you did what you were taught, then you should do that in class (while being aware that R will often disagree with your results).

For a too-long discussion of this issue (and references to others), see my blog: The Many Meanings of “Quartile”

Thank you, Dr. Peterson. I also read your blog, to get a better understanding.

 

[Dr.Peterson]

The median is 1. And the median of the upper range is 6.5 = (5+8)/2, which I got as the 3rd quartile. The median of the lower rannge is -7.5 = (-8+-7)/2, which I got as the 1st quartile.

What they are presumably doing is including the median as part of both lower and upper halves, whereas you are excluding it, as I expected. Both definitions are taught and used. For large data sets, this is less important than in small data sets used in class.

 

[Steven G]

The median is 1. And the median of the upper range is 6.5 = (5+8)/2, which I got as the 3rd quartile. The median of the lower rannge is -7.5 = (-8+-7)/2, which I got as the 1st quartile.

Looks good to me.