Are you asking how to do this programmatically or conceptually? You want to detect all values that are greater than three standard deviations from the mean.
Here's a demo with fake data to work through conceptually. In the plot, data outside of 3sd along the y axis are circled.
%fake data
rng(180)
d = normrnd(166,42,1,5000);
m = mean(d);
sd = std(d);
outliers = false(size(d));
outliers(d < m-sd*3) = true;
outliers(d > m+sd*3) = true;
figure
t = 1:length(d);
plot(t, d, 'b.')
hold on
plot(t(outliers), d(outliers), 'ro')
rh = refline(0,m);
set(rh, 'color', 'm')
rh2 = refline(0,m+sd*3);
rh3 = refline(0,m-sd*3);
set([rh2,rh3], 'color', 'm', 'linestyle', '--')
legend('data', 'outliers', 'mean', '3rd sd')
