A little math

[Arkady]

Just a helpful tip on some counter-intuitive math. Let's say I offer you one of two investments. The first will grow 50% in year one, then shrink 30% in year two. The second will grow 5% in year one and 5% in year two. Which would you prefer, other things being equal?

If you're not very good with math, you may think you can simply add percentage.s The first one would be 50%-30% for a 20% net gain. The second one would be 5%+5% for a 10% net gain. You might think the first investment is twice as good. Is it?

Well, let's try it out with real numbers, assuming an initial investment of $100.

Investment one:
Start: $100
+50%: $150
-30% of $150: $105

Investment two:
Start: $100
+5%: $105
+5% of $105: $110.25

Investment two is over twice as good.

I bring this up in reference to the way I ran the numbers for my presidential series. If you simply add up percentages, then you get a misleading view of which of two series is better. If, for example, GDP rises 5% in one Republican presidential era then falls 3% in the next Republican presidential era, that may look it would be better than having it rise half a percent in each of two eras, but it isn't. That's just not how percentages work. That's why you'll see that after I calculate the percentage gain or loss for each Republican and Democratic era, I then calculate cumulative gain or loss sequentially, rather than incorrectly just adding up the percentages.

 

[Deleted member 21794]

LOL.... you just discovered this???? No wonder you're having trouble with the rebuttals you're getting!

 

[Arkady]

LOL.... you just discovered this???? No wonder you're having trouble with the rebuttals you're getting!

No. You misunderstood. I didn't just discover this. IN fact, this isn't even the first time I've posted here to try to educate the right-wingers about this math fact -- I posted something similar years ago. But the ignorance persists (see Drumcollie's attempt to rebut my post by simply adding percentages), so it made sense to present it again. This is the kind of thing people with a decent math sense become aware of around the time they first learn about percentages in grade school, but right-wingers tend to be innumerate, so a little "adult education" is in order.

 

[Deleted member 21794]

No. You misunderstood. I didn't just discover this. IN fact, this isn't even the first time I've posted here to try to educate the right-wingers about this math fact -- I posted something similar years ago. But the ignorance persists (see Drumcollie's attempt to rebut my post by simply adding percentages), so it made sense to present it again. This is the kind of thing people with a decent math sense become aware of around the time they first learn about percentages in grade school, but right-wingers tend to be innumerate, so a little "adult education" is in order.

Given your inability to be able to read a simple graph and add percentages, you're in no position to lecture others about it. Besides, didn't you just lecture me about being in the wrong thread? So if you have an issue with Drumcollie in a thread, you should take it up with him in that thread- going by the standard you just declared.

 

[Arkady]

Given your inability to be able to read a simple graph and add percentages

You're imagining things again.

Besides, didn't you just lecture me about being in the wrong thread?

No. I let you know you were in the wrong thread in a single sentence. That's not what a lecture is. If you ever go to college, you'll learn that.

So if you have an issue with Drumcollie in a thread, you should take it up with him in that thread- going by the standard you just declared.

The point of going to the top post with this isn't to call out Drumcollie, which is why I didn't name names. It's to make posters, in general, aware of this fact, since I've seen the same error from multiple posters, and since it's relevant to understanding multiple first-tier posts I've made.