How do I do a regress like this?

2 次查看（过去 30 天）
Leon
Leon 2023-9-16
评论： Leon 2023-9-26
I have a series of numbers that decrease by about the same percetentage rate with time. How do I do the regression to find the exact percentage rate it is changing?
For example, it can be something like the below:
1 100
2 95
3 91
4 86
5 80
Many thanks.

请先登录，再回答此问题。

采纳的回答

Image Analyst
Image Analyst 2023-9-16
Ran in:
Not sure why you need a regression. How about this to just find out the percentage decrease at each time point. Then compute the average percentage decrease over all time points if you want.
y = [100, 95, 91, 86, 80];
deltaY = diff(y)
deltaY = 1×4
-5 -4 -5 -6
percentageDecreases = 100 * deltaY ./ y(1:end-1)
percentageDecreases = 1×4
-5.0000 -4.2105 -5.4945 -6.9767
averagePercentageDecrease = mean(percentageDecreases)
averagePercentageDecrease = -5.4204
  5 个评论
显示 3更早的评论
Image Analyst
Image Analyst 2023-9-19
fitnlm just needs a starting point for some reason. So what I usually do is to just put anything there. It will do it's best and then I use the returned, estimated coordinates for the guess next time and do it again. After a few times of this, the values should converge. You could put it in a loop and do it like 5 or 10 times and see how the values settle on the final, good values.

请先登录，再进行评论。

更多回答（1 个）

Sam Chak
Sam Chak 2023-9-16
Ran in:
Hi @Leon
I'm not exactly sure what you want. If you're looking to find the exact percentage drop, as @Image Analyst has shown you, that's one approach. If you want to use MATLAB to create a linear regression model fit, you can do so using the 'fitlm()' function.
y = [100, 95, 91, 86, 80]; % data
x = 1:numel(y);
mdl = fitlm(x, y) % linear regression model
mdl =
Linear regression model: y ~ 1 + x1 Estimated Coefficients: Estimate SE tStat pValue ________ _______ _______ __________ (Intercept) 105.1 0.63509 165.49 4.8652e-07 x1 -4.9 0.19149 -25.589 0.00013089 Number of observations: 5, Error degrees of freedom: 3 Root Mean Squared Error: 0.606 R-squared: 0.995, Adjusted R-Squared: 0.994 F-statistic vs. constant model: 655, p-value = 0.000131
plot(mdl)
  2 个评论
Leon
Leon 2023-9-16
Thanks for the reply.
The change should be exponential (e.g., 5% decrease during each time period), instead of linear (a fixed decrease rate of 5). In this case, how should I do the regression?
Sam Chak
Sam Chak 2023-9-16
Hi @Leon, you can refer to the example of the exponential regression shared by @Image Analyst.

请先登录，再进行评论。

类别

在 Help Center 和 File Exchange 中查找有关 Multiple Linear Regression 的更多信息

标签

产品


版本

R2023a

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by