How to remove regression line from qqplot?

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Hydro 2017-7-26

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/350397-how-to-remove-regression-line-from-qqplot

评论： Star Strider 2017-7-26

Hello all, For some reason, i don't want the auto fitted line (red in the picture)in my Q-Q plot. Is there any function to turned it off? here is my code for the picture attached. Also, any thoughts on how to add the Confidence Intervals?

qqplot(obs_high,M1_high); hold on
plot([0 400], [0 400])
xlabel('Observed streamflow (m^3/sec)')
ylabel('simulated streamflow (m^3/sec)')
title('Model-1');

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Answer 1

Star Strider 2017-7-26

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https://ww2.mathworks.cn/matlabcentral/answers/350397-how-to-remove-regression-line-from-qqplot#answer_275660

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Return a handle from your qqplot call, then find the line you want to remove, (experiment) and set its color to 'none'.

Example —

hqq = qqplot(obs_high,M1_high);
hqq(2).Color = 'none';

Note — I don’t know if the Line object referred to here as ‘hgg(2)’ is the one you want.

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Hydro 2017-7-26

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Hello Strider, Excellent, I got some ideas from your answers, here is what I have done and I got what I wanted. Many thanks. Any thoughts on the confidence interval for the Q-Q plot?

h = qqplot(obs_high, M1_high); hold on
plot([0 400], [0 400])
set(h, 'Color', 'w','MarkerEdgeColor', 'k')
xlabel('')
ylabel('Simulated streamflow (m^3/sec)')
title('Model-1')

Star Strider 2017-7-26

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Thank you. My pleasure.

The confidence intervals aren’t an option in qqplot itself, and I’m not certain how the quantiles or the regression line are calculated.

One option is to use fitlm to calculate the regression and the confidence intervals for the plot.

Example —

load gas
figure(1)
hqq = qqplot(price1);
XD = hqq(1).XData;
YD = hqq(1).YData;
mdl = fitlm(XD(:),YD(:));
[ypred,yci] = predict(mdl,XD(:));
figure(2)
plot(XD, YD, '+b')
hold on
plot(XD(:),ypred,'-r',   XD(:),yci,'--r')
hold off

However, the regression line is different from that calculated by qqplot, at least with these data. Since I rarely use qqplot and am not certain how it works internally, you will probably need to ask MathWorks how best to calculate the regression line and confidence intervals.

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