MATLAB: Need help plotting confidence intervals

confidence intervalMATLAB

Hi,
I'm trying to plot a 95% confidence interval in matlab but I can't get it the way I want.
What I'm trying to plot is something like this: https://explorable.com/images/statistics-confidence-interval.png
I've found a script which creates the polynomial but fills the area opposite:
 alpha = 0.05;           % significance level
mu = 82.9;              % mean
sigma = 8.698;          % std
cutoff1 = norminv(alpha, mu, sigma);
cutoff2 = norminv(1-alpha, mu, sigma);
x = [linspace(mu-4*sigma,cutoff1), ...
    linspace(cutoff1,cutoff2), ...
    linspace(cutoff2,mu+4*sigma)];
y = normpdf(x, mu, sigma);
plot(x,y, 'black')
xlo = [x(x<=cutoff1) cutoff1];
ylo = [y(x<=cutoff1) 0];
patch(xlo, ylo, 'black')
x = linespace(68,0.01,70;
y = linspace(0,0.01,0.045;
patch(x, y, 'r')
xhi = [cutoff2 x(x>=cutoff2)];
yhi = [0 y(x>=cutoff2)];
patch(xhi, yhi, 'black')
Can you guys help me make it the way I want?

Best Answer

alpha = 0.05;           % significance level
mu = 82.9;              % mean
sigma = 8.698;          % std
cutoff1 = norminv(alpha, mu, sigma);
cutoff2 = norminv(1-alpha, mu, sigma);
x = [linspace(mu-4*sigma,cutoff1), ...
    linspace(cutoff1,cutoff2), ...
    linspace(cutoff2,mu+4*sigma)];
y = normpdf(x, mu, sigma);
figure
plot(x,y, 'black')
% Lo black
xlo = [x(x<=cutoff1) cutoff1];
ylo = [y(x<=cutoff1) 0];
patch(xlo, ylo, 'black')
% Mid red
xmid = [x(x>=cutoff1 & x<=cutoff2) cutoff2 cutoff1];
ymid = [y(x>=cutoff1 & x<=cutoff2)       0       0];
patch(xmid, ymid, 'red')
% High black
xhi = [cutoff2 x(x>=cutoff2)];
yhi = [0 y(x>=cutoff2)];
patch(xhi, yhi, 'black')
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