how to calculate 99.9% confidence interval in matlab

To calculate a 99.9% confidence interval in Matlab, you can use the norminv function. The norminv function finds the value of the inverse of the cumulative distribution function of the normal distribution at a given probability level.

Here's an example code block that calculates a 99.9% confidence interval for a sample data set:

main.m
% Sample data set
data = [21 18 20 24 19 23 22 20 19 25];

% Calculate sample mean and standard deviation
sample_mean = mean(data);
sample_std = std(data);

% Set confidence level
conf_level = 0.999;

% Calculate critical value using 'norminv'
crit_val = norminv((1+conf_level)/2,0,1);

% Calculate margin of error
margin_of_error = crit_val * (sample_std/sqrt(length(data)));

% Calculate lower and upper bounds of confidence interval
lower_bound = sample_mean - margin_of_error;
upper_bound = sample_mean + margin_of_error;
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In this example, the norminv function is used to calculate the critical value for a 99.9% confidence interval. The critical value is calculated by taking the inverse of the cumulative distribution function of the normal distribution at a probability level of (1 + confidence level)/2. The margin_of_error is then calculated using the critical value and the standard error of the mean. Finally, the lower and upper bounds of the confidence interval are calculated by subtracting and adding the margin of error to the sample mean, respectively.