Gradient of a line

Tuppy_Glossop · 20 Jun 2014 at 12:47

Theophany said:
Each time you cut it in half, you essentially double the amount of sandwiches you have.

I love tuna... no bones

glenimp617 · 20 Jun 2014 at 12:47

BODMAS

Sliver · 20 Jun 2014 at 12:56

Theophany said:
Each time you cut it in half, you essentially double the amount of sandwiches you have.

Does this mean a bird in the hand is worth 2 in the bush ?

Theophany · 20 Jun 2014 at 13:00

Sliver said:
Does this mean a bird in the hand is worth 2 in the bush ?

Only if the following conditions are met:

a). Said birds are actually women
b). Said birds are **** of some genus

WillyNelson · 20 Jun 2014 at 13:05

D D Danneh said:
% increase is just the difference between months divided by the value of the first.

I know. I'm trying to calculate the long term trend.

All this talk of sandwiches is making me hungry... Lunch.

Tuppy_Glossop · 20 Jun 2014 at 13:06

WillyNelson said:
I know. I'm trying to calculate the long term trend.

All this talk of sandwiches is making me hungry... Lunch.

I answered it for you already :confused:

Haircut · 20 Jun 2014 at 13:17

WillyNelson said:
That's ok if you've got a constant increase from month to month, but I've got ups & downs. It's the long term trend that I want to get growth for.

Here's my data & the chart

What is the trend supposed to be showing here?
You haven't even got the months in date order so surely trying to get a trend line is meaningless?

touch · 20 Jun 2014 at 13:27

Haircut said:
What is the trend supposed to be showing here?
You haven't even got the months in date order so surely trying to get a trend line is meaningless?

The months are in order? :confused:

Shouldnt the gradient be the inverse of 119.45 and 396.05? These are multipliers of X but gradient is measured against the Y axis.

So 0.0084 and 0.0025
8% and 2.5% ?

Tuppy_Glossop · 20 Jun 2014 at 13:34

Ffs. For y=mx+c if c!=0 the gradient percentage is (m/c)*100, so y=119.45x+51062 gives (119.45/51062)*100 = 0.234%

Sunbed · 20 Jun 2014 at 14:01

^ I don't think that's right. Looking at OP's graph, the trendline starts at about 52000 and ends at 55000. Resulting in an overall % increase of 5.77%.

This is harder than I thought and now I'm stuck. OP this thread may help:
http://www.excelforum.com/excel-general/672000-trendlines.html

WillyNelson · 20 Jun 2014 at 14:01

Haircut said:
What is the trend supposed to be showing here?
You haven't even got the months in date order so surely trying to get a trend line is meaningless?

The trend in increased activity.

The months are by fiscal year not calendar year, so they are correct.

Tuppy_Glossop said:
Ffs. For y=mx+c if c!=0 the gradient percentage is (m/c)*100, so y=119.45x+51062 gives (119.45/51062)*100 = 0.234%

So the trend is an increase of 0.234% per period, ie over 10 months you'd expect to have growth of 2.34%? That makes more sense.

WillyNelson · 20 Jun 2014 at 14:03

Sunbed said:
^ I don't think that's right. Looking at OP's graph, the trendline starts at about 52000 and ends at 55000. Resulting in an overall % increase of 5.77%.

This is harder than I thought and now I'm stuck. OP this thread may help:
http://www.excelforum.com/excel-general/672000-trendlines.html

By my understanding of Tuppy's method it'd be 0.234%*19months = 4.446%, which sounds about right.

cheesyboy · 20 Jun 2014 at 14:13

WillyNelson said:
So the trend is an increase of 0.234% per period, ie over 10 months you'd expect to have growth of 2.34%? That makes more sense.

Not quite.

0.234 if the increase for one period. After one period, the calculation has changed (the m and c values in Tuppy's equation). If you look at the right hand column in my earlier chart, you'll see this effect in action.

Sunbed · 20 Jun 2014 at 14:15

Yeh it looks right but if I do a basic graph of this data:

Code:

Clearly the % increase is 40% and the equation is y=10x+90. Following Tummy's method:

(10/90)*100*number of periods (4) = 44.4% i.e. not right :confused:

cheesyboy · 20 Jun 2014 at 14:21

Sunbed said:
Yeh it looks right but if I do a basic graph of this data:

Code:

1 100 2 110 3 120 4 130 5 140

Clearly the % increase is 40% and the equation is y=10x+90. Following Tummy's method:

(10/90)*100*number of periods (4) = 44.4% i.e. not right

100 is really the starting point, rather than 90

10/90)*100*number of periods (4) = 40%

rubberduck · 20 Jun 2014 at 14:24

Ignoring the actual answer for a second, I'm not sure if you are analysing the data in a meaningful manner. Correct me if I'm wrong but aren't you just drawing a straight line between the first and last data point and saying that that is giving you the 'trend over time'. Who says there is a trend over time at all, perhaps what you are extrapolating is simply the scatter in the data?

cheesyboy · 20 Jun 2014 at 14:25

rubberduck said:
Ignoring the actual answer for a second, I'm not sure if you are analysing the data in a meaningful manner. Correct me if I'm wrong but aren't you just drawing a straight line between the first and last data point and saying that that is giving you the 'trend over time'. Who says there is a trend over time at all, perhaps what you are extrapolating is simply the scatter in the data?

Time to break out the good old Sum of squares?

WillyNelson · 20 Jun 2014 at 14:27

rubberduck said:
Ignoring the actual answer for a second, I'm not sure if you are analysing the data in a meaningful manner. Correct me if I'm wrong but aren't you just drawing a straight line between the first and last data point and saying that that is giving you the 'trend over time'. Who says there is a trend over time at all, perhaps what you are extrapolating is simply the scatter in the data?

No. It's a calculated trend line and you can see that it's not on the first & last data points but slightly below.

rubberduck · 20 Jun 2014 at 14:32

WillyNelson said:
No. It's a calculated trend line and you can see that it's not on the first & last data points but slightly below.

Fair enough, so what is the R-squared value of the trend line? That will tell you how well the trend-line fits the data set.

*edit* you should be able to get the value from excel

Tuppy_Glossop · 20 Jun 2014 at 14:35

The gradient percentage can't be used in that way. Say you go ten months from Apr-14 57181 you increase by 10*119.45=1194.5, which as a percentage is
(1194.5/57181)*100=2.09%