Bell Curve

[Susan Altemus]

I would like to determine a bell curve using performance ratings for our employees. Would someone be able to assist me?

I currently have 2 columns as shown below. The lowest rating someone could receive is a zero and the highest a five.

<TABLE style="WIDTH: 163pt; BORDER-COLLAPSE: collapse" cellSpacing=0 cellPadding=0 width=218 border=0 x:str><COLGROUP><COL style="WIDTH: 92pt; mso-width-source: userset; mso-width-alt: 4498" width=123><COL style="WIDTH: 71pt; mso-width-source: userset; mso-width-alt: 3474" width=95><TBODY><TR style="HEIGHT: 12.75pt" height=17><TD class=xl22 style="BORDER-RIGHT: #d4d0c8; BORDER-TOP: #d4d0c8; BORDER-LEFT: #d4d0c8; WIDTH: 92pt; BORDER-BOTTOM: #d4d0c8; HEIGHT: 12.75pt; BACKGROUND-COLOR: transparent" width=123 height=17>Employee</TD><TD class=xl23 style="BORDER-RIGHT: #d4d0c8; BORDER-TOP: #d4d0c8; BORDER-LEFT: #d4d0c8; WIDTH: 71pt; BORDER-BOTTOM: #d4d0c8; BACKGROUND-COLOR: transparent" width=95>Rating</TD></TR><TR style="HEIGHT: 12.75pt" height=17><TD class=xl22 style="BORDER-RIGHT: #d4d0c8; BORDER-TOP: #d4d0c8; BORDER-LEFT: #d4d0c8; BORDER-BOTTOM: #d4d0c8; HEIGHT: 12.75pt; BACKGROUND-COLOR: transparent" height=17>A</TD><TD class=xl23 style="BORDER-RIGHT: #d4d0c8; BORDER-TOP: #d4d0c8; BORDER-LEFT: #d4d0c8; BORDER-BOTTOM: #d4d0c8; BACKGROUND-COLOR: transparent" x:num>3.25</TD></TR><TR style="HEIGHT: 12.75pt" height=17><TD class=xl22 style="BORDER-RIGHT: #d4d0c8; BORDER-TOP: #d4d0c8; BORDER-LEFT: #d4d0c8; BORDER-BOTTOM: #d4d0c8; HEIGHT: 12.75pt; BACKGROUND-COLOR: transparent" height=17>B</TD><TD class=xl23 style="BORDER-RIGHT: #d4d0c8; BORDER-TOP: #d4d0c8; BORDER-LEFT: #d4d0c8; BORDER-BOTTOM: #d4d0c8; BACKGROUND-COLOR: transparent" x:num>3.15</TD></TR><TR style="HEIGHT: 12.75pt" height=17><TD class=xl22 style="BORDER-RIGHT: #d4d0c8; BORDER-TOP: #d4d0c8; BORDER-LEFT: #d4d0c8; BORDER-BOTTOM: #d4d0c8; HEIGHT: 12.75pt; BACKGROUND-COLOR: transparent" height=17>C</TD><TD class=xl23 style="BORDER-RIGHT: #d4d0c8; BORDER-TOP: #d4d0c8; BORDER-LEFT: #d4d0c8; BORDER-BOTTOM: #d4d0c8; BACKGROUND-COLOR: transparent" x:num>3.00</TD></TR><TR style="HEIGHT: 12.75pt" height=17><TD class=xl22 style="BORDER-RIGHT: #d4d0c8; BORDER-TOP: #d4d0c8; BORDER-LEFT: #d4d0c8; BORDER-BOTTOM: #d4d0c8; HEIGHT: 12.75pt; BACKGROUND-COLOR: transparent" height=17>D</TD><TD class=xl23 style="BORDER-RIGHT: #d4d0c8; BORDER-TOP: #d4d0c8; BORDER-LEFT: #d4d0c8; BORDER-BOTTOM: #d4d0c8; BACKGROUND-COLOR: transparent" x:num>2.75</TD></TR><TR style="HEIGHT: 12.75pt" height=17><TD class=xl22 style="BORDER-RIGHT: #d4d0c8; BORDER-TOP: #d4d0c8; BORDER-LEFT: #d4d0c8; BORDER-BOTTOM: #d4d0c8; HEIGHT: 12.75pt; BACKGROUND-COLOR: transparent" height=17>E</TD><TD class=xl23 style="BORDER-RIGHT: #d4d0c8; BORDER-TOP: #d4d0c8; BORDER-LEFT: #d4d0c8; BORDER-BOTTOM: #d4d0c8; BACKGROUND-COLOR: transparent" x:num>3.20</TD></TR><TR style="HEIGHT: 12.75pt" height=17><TD class=xl22 style="BORDER-RIGHT: #d4d0c8; BORDER-TOP: #d4d0c8; BORDER-LEFT: #d4d0c8; BORDER-BOTTOM: #d4d0c8; HEIGHT: 12.75pt; BACKGROUND-COLOR: transparent" height=17>F</TD><TD class=xl23 style="BORDER-RIGHT: #d4d0c8; BORDER-TOP: #d4d0c8; BORDER-LEFT: #d4d0c8; BORDER-BOTTOM: #d4d0c8; BACKGROUND-COLOR: transparent" x:num>3.00</TD></TR><TR style="HEIGHT: 12.75pt" height=17><TD class=xl22 style="BORDER-RIGHT: #d4d0c8; BORDER-TOP: #d4d0c8; BORDER-LEFT: #d4d0c8; BORDER-BOTTOM: #d4d0c8; HEIGHT: 12.75pt; BACKGROUND-COLOR: transparent" height=17>G</TD><TD class=xl23 style="BORDER-RIGHT: #d4d0c8; BORDER-TOP: #d4d0c8; BORDER-LEFT: #d4d0c8; BORDER-BOTTOM: #d4d0c8; BACKGROUND-COLOR: transparent" x:num>3.10</TD></TR><TR style="HEIGHT: 12.75pt" height=17><TD class=xl22 style="BORDER-RIGHT: #d4d0c8; BORDER-TOP: #d4d0c8; BORDER-LEFT: #d4d0c8; BORDER-BOTTOM: #d4d0c8; HEIGHT: 12.75pt; BACKGROUND-COLOR: transparent" height=17>H</TD><TD class=xl23 style="BORDER-RIGHT: #d4d0c8; BORDER-TOP: #d4d0c8; BORDER-LEFT: #d4d0c8; BORDER-BOTTOM: #d4d0c8; BACKGROUND-COLOR: transparent" x:num>2.85</TD></TR><TR style="HEIGHT: 12.75pt" height=17><TD class=xl22 style="BORDER-RIGHT: #d4d0c8; BORDER-TOP: #d4d0c8; BORDER-LEFT: #d4d0c8; BORDER-BOTTOM: #d4d0c8; HEIGHT: 12.75pt; BACKGROUND-COLOR: transparent" height=17>I</TD><TD class=xl23 style="BORDER-RIGHT: #d4d0c8; BORDER-TOP: #d4d0c8; BORDER-LEFT: #d4d0c8; BORDER-BOTTOM: #d4d0c8; BACKGROUND-COLOR: transparent" x:num>4.50</TD></TR><TR style="HEIGHT: 12.75pt" height=17><TD class=xl22 style="BORDER-RIGHT: #d4d0c8; BORDER-TOP: #d4d0c8; BORDER-LEFT: #d4d0c8; BORDER-BOTTOM: #d4d0c8; HEIGHT: 12.75pt; BACKGROUND-COLOR: transparent" height=17>K</TD><TD class=xl23 style="BORDER-RIGHT: #d4d0c8; BORDER-TOP: #d4d0c8; BORDER-LEFT: #d4d0c8; BORDER-BOTTOM: #d4d0c8; BACKGROUND-COLOR: transparent" x:num>5.00</TD></TR><TR style="HEIGHT: 12.75pt" height=17><TD class=xl22 style="BORDER-RIGHT: #d4d0c8; BORDER-TOP: #d4d0c8; BORDER-LEFT: #d4d0c8; BORDER-BOTTOM: #d4d0c8; HEIGHT: 12.75pt; BACKGROUND-COLOR: transparent" height=17>L</TD><TD class=xl23 style="BORDER-RIGHT: #d4d0c8; BORDER-TOP: #d4d0c8; BORDER-LEFT: #d4d0c8; BORDER-BOTTOM: #d4d0c8; BACKGROUND-COLOR: transparent" x:num>3.50</TD></TR><TR style="HEIGHT: 12.75pt" height=17><TD class=xl22 style="BORDER-RIGHT: #d4d0c8; BORDER-TOP: #d4d0c8; BORDER-LEFT: #d4d0c8; BORDER-BOTTOM: #d4d0c8; HEIGHT: 12.75pt; BACKGROUND-COLOR: transparent" height=17>M</TD><TD class=xl23 style="BORDER-RIGHT: #d4d0c8; BORDER-TOP: #d4d0c8; BORDER-LEFT: #d4d0c8; BORDER-BOTTOM: #d4d0c8; BACKGROUND-COLOR: transparent" x:num>3.75</TD></TR><TR style="HEIGHT: 12.75pt" height=17><TD class=xl22 style="BORDER-RIGHT: #d4d0c8; BORDER-TOP: #d4d0c8; BORDER-LEFT: #d4d0c8; BORDER-BOTTOM: #d4d0c8; HEIGHT: 12.75pt; BACKGROUND-COLOR: transparent" height=17>N</TD><TD class=xl23 style="BORDER-RIGHT: #d4d0c8; BORDER-TOP: #d4d0c8; BORDER-LEFT: #d4d0c8; BORDER-BOTTOM: #d4d0c8; BACKGROUND-COLOR: transparent" x:num>3.85</TD></TR></TBODY></TABLE>

Thank you,
Susie

 

[SamTYler]

Add third column("C") Percentage "grade"

Formula in "C2":= "=B2/5"

Copy formula down to bottom

Sort table on column("B") ascending

Use Chart wizard, Data in "C," labels in "A"

 

[Susan Altemus]

Thank you Sam, but I am still not getting an actual bell curve. I had done it once before, but can't remember how I did it. I used StdDev and NormDist.

Susie

 

[SamTYler]

I used StdDev and NormDist.

Now you're outa my league, Suzan. Sorry. What I know about bell curves can be written in the 99.999 percentile.

 

[tusharm]

You cannot guarantee a bell curve from any particular data set.

Create a histogram for the ratings data. Adjust the default bucket values if that helps, but that's about the best that one can do.

I would like to determine a bell curve using performance ratings for our employees. Would someone be able to assist me?

I currently have 2 columns as shown below. The lowest rating someone could receive is a zero and the highest a five.

<TABLE style="WIDTH: 163pt; BORDER-COLLAPSE: collapse" cellSpacing=0 cellPadding=0 width=218 border=0 x:str><COLGROUP><COL style="WIDTH: 92pt; mso-width-source: userset; mso-width-alt: 4498" width=123><COL style="WIDTH: 71pt; mso-width-source: userset; mso-width-alt: 3474" width=95><TBODY><TR style="HEIGHT: 12.75pt" height=17><TD class=xl22 style="BORDER-RIGHT: #d4d0c8; BORDER-TOP: #d4d0c8; BORDER-LEFT: #d4d0c8; WIDTH: 92pt; BORDER-BOTTOM: #d4d0c8; HEIGHT: 12.75pt; BACKGROUND-COLOR: transparent" width=123 height=17>Employee</TD><TD class=xl23 style="BORDER-RIGHT: #d4d0c8; BORDER-TOP: #d4d0c8; BORDER-LEFT: #d4d0c8; WIDTH: 71pt; BORDER-BOTTOM: #d4d0c8; BACKGROUND-COLOR: transparent" width=95>Rating</TD></TR><TR style="HEIGHT: 12.75pt" height=17><TD class=xl22 style="BORDER-RIGHT: #d4d0c8; BORDER-TOP: #d4d0c8; BORDER-LEFT: #d4d0c8; BORDER-BOTTOM: #d4d0c8; HEIGHT: 12.75pt; BACKGROUND-COLOR: transparent" height=17>A</TD><TD class=xl23 style="BORDER-RIGHT: #d4d0c8; BORDER-TOP: #d4d0c8; BORDER-LEFT: #d4d0c8; BORDER-BOTTOM: #d4d0c8; BACKGROUND-COLOR: transparent" x:num>3.25</TD></TR><TR style="HEIGHT: 12.75pt" height=17><TD class=xl22 style="BORDER-RIGHT: #d4d0c8; BORDER-TOP: #d4d0c8; BORDER-LEFT: #d4d0c8; BORDER-BOTTOM: #d4d0c8; HEIGHT: 12.75pt; BACKGROUND-COLOR: transparent" height=17>B</TD><TD class=xl23 style="BORDER-RIGHT: #d4d0c8; BORDER-TOP: #d4d0c8; BORDER-LEFT: #d4d0c8; BORDER-BOTTOM: #d4d0c8; BACKGROUND-COLOR: transparent" x:num>3.15</TD></TR><TR style="HEIGHT: 12.75pt" height=17><TD class=xl22 style="BORDER-RIGHT: #d4d0c8; BORDER-TOP: #d4d0c8; BORDER-LEFT: #d4d0c8; BORDER-BOTTOM: #d4d0c8; HEIGHT: 12.75pt; BACKGROUND-COLOR: transparent" height=17>C</TD><TD class=xl23 style="BORDER-RIGHT: #d4d0c8; BORDER-TOP: #d4d0c8; BORDER-LEFT: #d4d0c8; BORDER-BOTTOM: #d4d0c8; BACKGROUND-COLOR: transparent" x:num>3.00</TD></TR><TR style="HEIGHT: 12.75pt" height=17><TD class=xl22 style="BORDER-RIGHT: #d4d0c8; BORDER-TOP: #d4d0c8; BORDER-LEFT: #d4d0c8; BORDER-BOTTOM: #d4d0c8; HEIGHT: 12.75pt; BACKGROUND-COLOR: transparent" height=17>D</TD><TD class=xl23 style="BORDER-RIGHT: #d4d0c8; BORDER-TOP: #d4d0c8; BORDER-LEFT: #d4d0c8; BORDER-BOTTOM: #d4d0c8; BACKGROUND-COLOR: transparent" x:num>2.75</TD></TR><TR style="HEIGHT: 12.75pt" height=17><TD class=xl22 style="BORDER-RIGHT: #d4d0c8; BORDER-TOP: #d4d0c8; BORDER-LEFT: #d4d0c8; BORDER-BOTTOM: #d4d0c8; HEIGHT: 12.75pt; BACKGROUND-COLOR: transparent" height=17>E</TD><TD class=xl23 style="BORDER-RIGHT: #d4d0c8; BORDER-TOP: #d4d0c8; BORDER-LEFT: #d4d0c8; BORDER-BOTTOM: #d4d0c8; BACKGROUND-COLOR: transparent" x:num>3.20</TD></TR><TR style="HEIGHT: 12.75pt" height=17><TD class=xl22 style="BORDER-RIGHT: #d4d0c8; BORDER-TOP: #d4d0c8; BORDER-LEFT: #d4d0c8; BORDER-BOTTOM: #d4d0c8; HEIGHT: 12.75pt; BACKGROUND-COLOR: transparent" height=17>F</TD><TD class=xl23 style="BORDER-RIGHT: #d4d0c8; BORDER-TOP: #d4d0c8; BORDER-LEFT: #d4d0c8; BORDER-BOTTOM: #d4d0c8; BACKGROUND-COLOR: transparent" x:num>3.00</TD></TR><TR style="HEIGHT: 12.75pt" height=17><TD class=xl22 style="BORDER-RIGHT: #d4d0c8; BORDER-TOP: #d4d0c8; BORDER-LEFT: #d4d0c8; BORDER-BOTTOM: #d4d0c8; HEIGHT: 12.75pt; BACKGROUND-COLOR: transparent" height=17>G</TD><TD class=xl23 style="BORDER-RIGHT: #d4d0c8; BORDER-TOP: #d4d0c8; BORDER-LEFT: #d4d0c8; BORDER-BOTTOM: #d4d0c8; BACKGROUND-COLOR: transparent" x:num>3.10</TD></TR><TR style="HEIGHT: 12.75pt" height=17><TD class=xl22 style="BORDER-RIGHT: #d4d0c8; BORDER-TOP: #d4d0c8; BORDER-LEFT: #d4d0c8; BORDER-BOTTOM: #d4d0c8; HEIGHT: 12.75pt; BACKGROUND-COLOR: transparent" height=17>H</TD><TD class=xl23 style="BORDER-RIGHT: #d4d0c8; BORDER-TOP: #d4d0c8; BORDER-LEFT: #d4d0c8; BORDER-BOTTOM: #d4d0c8; BACKGROUND-COLOR: transparent" x:num>2.85</TD></TR><TR style="HEIGHT: 12.75pt" height=17><TD class=xl22 style="BORDER-RIGHT: #d4d0c8; BORDER-TOP: #d4d0c8; BORDER-LEFT: #d4d0c8; BORDER-BOTTOM: #d4d0c8; HEIGHT: 12.75pt; BACKGROUND-COLOR: transparent" height=17>I</TD><TD class=xl23 style="BORDER-RIGHT: #d4d0c8; BORDER-TOP: #d4d0c8; BORDER-LEFT: #d4d0c8; BORDER-BOTTOM: #d4d0c8; BACKGROUND-COLOR: transparent" x:num>4.50</TD></TR><TR style="HEIGHT: 12.75pt" height=17><TD class=xl22 style="BORDER-RIGHT: #d4d0c8; BORDER-TOP: #d4d0c8; BORDER-LEFT: #d4d0c8; BORDER-BOTTOM: #d4d0c8; HEIGHT: 12.75pt; BACKGROUND-COLOR: transparent" height=17>K</TD><TD class=xl23 style="BORDER-RIGHT: #d4d0c8; BORDER-TOP: #d4d0c8; BORDER-LEFT: #d4d0c8; BORDER-BOTTOM: #d4d0c8; BACKGROUND-COLOR: transparent" x:num>5.00</TD></TR><TR style="HEIGHT: 12.75pt" height=17><TD class=xl22 style="BORDER-RIGHT: #d4d0c8; BORDER-TOP: #d4d0c8; BORDER-LEFT: #d4d0c8; BORDER-BOTTOM: #d4d0c8; HEIGHT: 12.75pt; BACKGROUND-COLOR: transparent" height=17>L</TD><TD class=xl23 style="BORDER-RIGHT: #d4d0c8; BORDER-TOP: #d4d0c8; BORDER-LEFT: #d4d0c8; BORDER-BOTTOM: #d4d0c8; BACKGROUND-COLOR: transparent" x:num>3.50</TD></TR><TR style="HEIGHT: 12.75pt" height=17><TD class=xl22 style="BORDER-RIGHT: #d4d0c8; BORDER-TOP: #d4d0c8; BORDER-LEFT: #d4d0c8; BORDER-BOTTOM: #d4d0c8; HEIGHT: 12.75pt; BACKGROUND-COLOR: transparent" height=17>M</TD><TD class=xl23 style="BORDER-RIGHT: #d4d0c8; BORDER-TOP: #d4d0c8; BORDER-LEFT: #d4d0c8; BORDER-BOTTOM: #d4d0c8; BACKGROUND-COLOR: transparent" x:num>3.75</TD></TR><TR style="HEIGHT: 12.75pt" height=17><TD class=xl22 style="BORDER-RIGHT: #d4d0c8; BORDER-TOP: #d4d0c8; BORDER-LEFT: #d4d0c8; BORDER-BOTTOM: #d4d0c8; HEIGHT: 12.75pt; BACKGROUND-COLOR: transparent" height=17>N</TD><TD class=xl23 style="BORDER-RIGHT: #d4d0c8; BORDER-TOP: #d4d0c8; BORDER-LEFT: #d4d0c8; BORDER-BOTTOM: #d4d0c8; BACKGROUND-COLOR: transparent" x:num>3.85</TD></TR></TBODY></TABLE>

Thank you,
Susie

 

[samfolds]

If you want, you can force a normal shape to a distribution by using the average function, the stdev function and the norm function.

First, calculate the mean (=Average of all the ratings) and the standard deviation(=Stddev of all the ratings).

Then on a new column, insert values representing the ratings (be very wide - start in the negatives - and choose little jumps, perhaps 0.01)

On the column next to the last one, use this formula and drop down :

(Assuming you put the ratings in D1 and down and that your average is in cell B17 and stddev in B18)

=normdist(D1,$B$17,$B$18,FALSE)

Then use the graphic tool and use scatter. Voila, you "forced" your data to take the shape of a bell curve.

Interesting note : If you have a large amount of data, the graphic should take the bell shape without forcing it.

If you have any question don't hesitate.

Samfolds

 

[xenou]

If you want, you can force a normal shape to a distribution by using the average function, the stdev function and the norm function.

If I may ask out of curiosity, why would you do this? For the sake of argument, let's say the data is not a normal curve. What do we gain by "forcing" it into a normal curve (whatever that means)?

Then on a new column, insert values representing the ratings (be very wide - start in the negatives - and choose little jumps, perhaps 0.01)

Also curious on this point, what does it mean to use values representing ratings? What has happened to the real ratings?

 

[tusharm]

To learn more about this (after calculating the mean and std. dev.), see
Drawing a Normal curve
http://www.tushar-mehta.com/excel/charts/normal_distribution/

If you want, you can force a normal shape to a distribution by using the average function, the stdev function and the norm function.

First, calculate the mean (=Average of all the ratings) and the standard deviation(=Stddev of all the ratings).

Then on a new column, insert values representing the ratings (be very wide - start in the negatives - and choose little jumps, perhaps 0.01)

On the column next to the last one, use this formula and drop down :

(Assuming you put the ratings in D1 and down and that your average is in cell B17 and stddev in B18)

=normdist(D1,$B$17,$B$18,FALSE)

Then use the graphic tool and use scatter. Voila, you "forced" your data to take the shape of a bell curve.

Interesting note : If you have a large amount of data, the graphic should take the bell shape without forcing it.

If you have any question don't hesitate.

Samfolds

 

[tusharm]

LOL!

Have you heard of "There are three kinds of lies: lies, damned lies, and statistics?"

Mark Twain attributed the quote to Benjamin Disraeli but it might have been Charles Wentworth Dilke.

Try the following. It's something I did before my first post in this discussion.

Create a histogram using Excel's Data Analysis tool, w/o specifying the bin range and checking the 'Chart Output' option.

Next, do the same except this time specify a bin range that contains the values 2.75, 3, ..., 4.25, 4.5.

Finally, use a bin range of 3, 3.5, etc.

See the shapes of the 3 charts? You can make the data look skewed or "normal-ish" depending on your point of view.

If I may ask out of curiosity, why would you do this? For the sake of argument, let's say the data is not a normal curve. What do we gain by "forcing" it into a normal curve (whatever that means)?


Also curious on this point, what does it mean to use values representing ratings? What has happened to the real ratings?

 

[samfolds]

If I may ask out of curiosity, why would you do this? For the sake of argument, let's say the data is not a normal curve. What do we gain by "forcing" it into a normal curve (whatever that means)?

The normal curve is really nice looking :P and is easy to work with (for example, you can use the central limit theorem). Furthermore, after collecting a large enough sample of data, the distribution will be very very close to a normal distribution (regardless of the individual distribution of the ratings). Note that it is an APPROXIMATION (but as stated, so easy to work with)

Also curious on this point, what does it mean to use values representing ratings? What has happened to the real ratings?

If you use your actual data (with a small sample), the graph won't look like a normal curve. Therefore, you plot a large amout of possible values, all corresponding to a normal distr.

Hope this helps.

Samfolds