So, Paul, do you want to calculate year-to-year changes, or do you want to
calculate how much each year's figure has changed as compared to the base year?
--
Charles Knell
cknell(_at_)onebox(_dot_)com - email
-----Original Message-----
From: Paul Tremblay <phthenry(_at_)earthlink(_dot_)net>
Sent: Fri, 19 Dec 2003 04:29:53 -0500
To: xsl-list(_at_)lists(_dot_)mulberrytech(_dot_)com
Subject: Re: [xsl] Re: summing up incrementally
On Fri, Dec 19, 2003 at 07:12:36AM +0100, Dimitre Novatchev wrote:
It is quite simple to see that the real comulative increase is the product
of percentages of yearly increases, not their sum.
E.g. two yearly increases of 50% each give 225% comulative increase. That is
1.5 x 1.5, or it may be calculated:
In case the value is 100 at start, it would be 150 after year 1.
An increase of 50% the second year is 50% of 150 -- that is 75.
The value at the end of the second year is 150 + 75 = 225
Therefore, the total increase is: 225/100 = 2.25 = 225%
Your approach to calculating the total increase is wrong -- e.g. in the
above case it woud give 100%, not 225%.
I see your reasoning. In fact, I cannot add up percentages. That gives
me a false value.
But I calculate percent increase by this formula:
% increase = (new -old)/old * 100
If someone says that their profits increased 100 percent, this usually
means it has doubled in value. Perhaps a mathmatician would correct me.
However, the modern high school math books teach percentage increase in
this way.
In your example, I would say that 225 has increased 125 percent from
100. I realize that technically this might be wrong (1.25 * 100 = 125).
On the other hand, if you are graphing the increase, you want to have
these figures:
Graph showing percentage increase for first three years
====================================================== x y
= 1 0
2 50
3 125
The slopes of the lines would be identical if you plotted raw data:
Graph showing raw profits for first three years
============================================== x y
= 1 100
2 150
3 225
Here is a partial representation of the real figures:
year sales % increase from last year
==== ===== ======================== 1933: 250,516,527 ---
1934: 270,684,797 108
1935: 268,740,483 100
1936: 290,386,935 108
The thesis--actually my girlfriend's thesis--tries to show that as
Woolworth chainstores modernized its buildings, its profits increased. I
want to make a line graph to illustrate this point.
These figures come from the publication itself. However, I just checked
them, using this formula:
% increase = (year - previousYear)/perviousYear * 100
Originally I had added the percentages to get a 16 percent increase by
year 1936 from 1933. If you work the math the right way ((new - old)/new
* 100), you come up with 16 percent. If you add the figures, you also
come up with 16 percent.
But of course, that is a mere coincidence. As you pointed out, you
cannot add up percentages.
To caculate the figures is to use 1933 as a base year. Hence, this
formula:
% increase = (year - 250,516,527)/250,516,527 * 100
So for the 1934:
% = (270,684,797 - 250,516,527)/250,516,527 * 100 = 8
For 1935:
% = (268,740,483 - 250,516,527)/250,516,527 * 100 = 8
For 1936:
% = (290,386,935 - 250,516,527)/250,516,527 * 100 = 16
Or, if I do it your way:
1.08 * 1.00 * 1.08 = 1.16
Then subtract 100%, or 1, and I get the same answer. Okay, that makes
sense! If you start your graph at 0 rather than 100, you simply subract
100 from the result, as I did above.
Luckily, I entered the raw data in my XML as well as the percent
increase. I so simply did:
<xsl:vaiable name = "base-year" select = "/data/year[1]/record[(_at_)month
'December']/@target-year-to-date"/>
Then, when I want to find the percent increase, I can do:
<xsl:value-of select = "round((@target-year-to-date -
$base-year)/$base-year * 100)"/>
As I said in the last post, this math doesn't take inflation into
account. From 1934 to 1942, Woolworth increased around 70 percent.
Perhaps their sales did really increase this much; but I think inflation
would probably bring the number down.
Sorry this post is so long. I started off by thinking you didn't
understand my problem. Then I thought that you might be partially wrong.
And as I wrote it I realized you were completely correct.
Paul
--
PS 225 is 225% of 100
225 shows a 125% increase from 100
I think both these statements are correct?
************************
*Paul Tremblay *
*phthenry(_at_)earthlink(_dot_)net*
************************
XSL-List info and archive: http://www.mulberrytech.com/xsl/xsl-list
XSL-List info and archive: http://www.mulberrytech.com/xsl/xsl-list