My 2nd issue today is that I can’t figure out what is going on with the trend line equations. I have this particular chart to which I have fit a 4th order polynomial trend line. It looks great – just what I would expect. However when I plug the x values into the equation it has provided, I do not get the y values that it is plotting! The whole purpose of this exercise was to come up with this equation so that we can make estimates based on it. Is there something I’m not properly understanding in the way this equation is represented?
For example if I plug in 15 I get:
(.000003 * 15^4) – (.0002 * 15^3) + (.0034 * 15^2) – (.0162 * 15) + .028 =
(.000003 * 50,625) – (.0002 * 3,375) + (.0034 * 225) – (.0162 * 15) + .028 =
0.1519 -0.675 + 0.765 – 0.243 + 0.28 = 0.0269 or 2.69%
But the graph plots it at about 7.1% which is what fits the data.
I've attached a copy of the chart in question.
Here is the data:
3-Day Average
1 0.7%
2 0.5%
3 0.4%
4 0.7%
5 1.0%
6 2.4%
7 3.8%
8 4.4%
9 5.2%
10 6.4%
11 6.9%
12 7.3%
13 6.8%
14 6.8%
15 7.2%
16 6.9%
17 6.8%
18 6.8%
19 5.7%
20 4.5%
21 3.5%
22 2.5%
23 1.8%
24 1.0%
For example if I plug in 15 I get:
(.000003 * 15^4) – (.0002 * 15^3) + (.0034 * 15^2) – (.0162 * 15) + .028 =
(.000003 * 50,625) – (.0002 * 3,375) + (.0034 * 225) – (.0162 * 15) + .028 =
0.1519 -0.675 + 0.765 – 0.243 + 0.28 = 0.0269 or 2.69%
But the graph plots it at about 7.1% which is what fits the data.
I've attached a copy of the chart in question.
Here is the data:
3-Day Average
1 0.7%
2 0.5%
3 0.4%
4 0.7%
5 1.0%
6 2.4%
7 3.8%
8 4.4%
9 5.2%
10 6.4%
11 6.9%
12 7.3%
13 6.8%
14 6.8%
15 7.2%
16 6.9%
17 6.8%
18 6.8%
19 5.7%
20 4.5%
21 3.5%
22 2.5%
23 1.8%
24 1.0%