Plotting Normal Dirstribution/ bell curve

[#1]

Hi

I am trying to plot a Normal Distribution curve over the following barchart of sales increase.

Sales increase is a decimal representing the % increase.

I have tried a number of expressions but I'm having no luck,

I've tried using the NORMDIST function which I've played around but it isnt working, as well as creating an expression from scratch.

normdist(salesInc,avg(salesInc),stdev(salesInc))

for the graph I use the

dimension class(salesInc,5)

expression count(salesInc)

I'd be greatfull if you could point me in the right direction or show me some qlikview examples of normaldistribution,

[swuehl]

That's probably because salesInc is ambiguous for all classes with a frequency higher than 1.

If you want a sampling point in the center of your class width, try maybe

(floor(salesInc,5)+ceil(salesInc, 5))/2

like

normdist( (floor(salesInc,5)+ceil(salesInc, 5))/2,avg({1} total salesInc),stdev({1} total salesInc),0 )

[#3]

Thanks for the suggestion but still no luck

These are the figures that the expression is producing

0.0008
0.0051
-
-
-
-
-
-
0.0012
0.0001
0.0000
0.0000
0.0000
-

[swuehl]

Ah, sure, the same problem will persist using just floor() or ceil() function. Hm, maybe:

normdist( (floor(min(salesInc),5)+ceil(min(salesInc), 5))/2,avg({1} total salesInc),stdev({1} total salesInc),0 )

[#5]

This is the answer I'm getting, it is generating an answer for all the ranges now, however the numbers dont look like how I would expect

	Frequency
-20 <= x < -15	1	8.5E-5
-15 <= x < -10	1	0.051645999
-10 <= x < -5	6	0.250697235
-5 <= x < 0	28	0.526009038
0 <= x < 5	86	3.593327034
5 <= x < 10	29	1.211703302
10 <= x < 15	5	0.230117249
15 <= x < 20	3	0.168979575
20 <= x < 25	1	4.1E-16
25 <= x < 30	1	0.006841735
30 <= x < 35	1	9.2E-6
40 <= x < 45	1	1.4E-10
45 <= x < 50	1	1.4E-10
-	20	-

[swuehl]

You are getting numbers larger that 1 using only the normdist() function?

What numbers do you expect?

[#7]

For a normal distribution curve the numbers should start off small, get bigger(around the mean) and get small again to create a bell curve.

Where as for the first range the number is 8.5, when it should be smaller than the result for the second range.

[swuehl]

Again, I doubt that this is the outcome of just a normdist() function. What is the exact expression you are using?

For the first range, the number is not 8.5, but 8.5E-5, i.e. 0.000085.

[#9]

Thanks, I over looked that. but I expect the numbers to be higher, a closer value to those in the frequency column.

normdist( (floor(min(salesInc),5)+ceil(min(salesInc), 5))/2,avg({1} total salesInc),stdev({1} total salesInc),0 )

* Count(DISTINCT(SalesId))

for the frequency column I am using -

Count(DISTINCT(SalesId))  

in excel if I was to do this I would perform (normdist-previousNormDist)*totalFrequency and it works.

[swuehl]

I think

Count(DISTINCT(SalesId))

is not the correct factor to norm your bell curve so it does match your numbers.

I think you need to take the total number of SalesId into account:

count(TOTAL DISTINCT SalesId)

Hm, what about your class width? I think you also need to correct for that (so try an additional factor 0.2 (or 5?)

I don't have anymore time today, but maybe you are on the right path already.

[manideep78]

Hi John Witherspoon

I have the same requirement on the Bell Curve. After a lot of research I could find that your answer is nearer to what I actually need. I did not understood that in the above post why you are multiplying the expression with 600. I did not understood that. Can you please explain me that?

Regards

Manideep