Need help plotting confidence intervals

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?

Answer 1

[the cyclist]

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')

Answer 2

[Star Strider]

alpha = 0.05;           % significance level
mu = 82.9;              % mean
sigma = 8.698;          % std
x = linspace(mu-5*sigma, mu+5*sigma, 500);
cutoff1 = norminv(alpha/2, mu, sigma);          % Lower 95% CI is p = 0.025
cutoff2 = norminv(1-alpha/2, mu, sigma);        % Upper 95% CI is p = 0.975
y = normpdf(x, mu, sigma);
xci = [linspace(mu-5*sigma, cutoff1); linspace(cutoff2, mu+5*sigma)];
yci = normpdf(xci, mu, sigma);

figure(1)
plot(x, y, '-k', 'LineWidth', 1.5)
patch(x, y, [0.5 0.5 0.5])
patch([xci(1,:) cutoff1], [yci(1,:) 0], [1 1 1])
patch([cutoff2 xci(2,:)], [0 yci(2,:)], [1 1 1])

Answer 3

[Andreas]

Exactly, thanks!