To calculate the confidence interval, you first need to determine the mean, standard deviation, and sample size of the data set. Then, use the formula, (mean – (1.96*standard deviation/sqrt(sample size)), (mean + (1.96*standard deviation/sqrt(sample size)) to calculate the lower and upper bounds of the confidence interval. The number 1.96 is used because it is the z-score that corresponds to a 95% confidence level.
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This calculator creates a using the following formula:
Confidence Interval = x +/- z*(s/√n)
where:
- x: sample mean
- z: z-value that corresponds to confidence level
- s: sample standard deviation
- n: sample size
To create a confidence interval for a population mean, simply fill in the values below and then click the “Calculate” button:
90% Confidence Interval: (5.896, 28.104)
95% Confidence Interval: (3.770, 30.230)
99% Confidence Interval: (-0.388, 34.388)
function calc() {
//get input degrees of freedom, t-value
var mean = document.getElementById(‘mean’).value*1;
var sd = document.getElementById(‘sd’).value*1;
var n = document.getElementById(‘n’).value*1;
//define z-scores to use
var z_90 = 1.645;
var z_95 = 1.96;
var z_99 = 2.576;
//calculate intervals
var low_90 = mean – (z_90 * (sd/(Math.sqrt(n))));
var high_90 = mean – (-1*(z_90 * (sd/(Math.sqrt(n)))));
var low_95 = mean – (z_95 * (sd/(Math.sqrt(n))));
var high_95 = mean – (-1*(z_95 * (sd/(Math.sqrt(n)))));
var low_99 = mean – (z_99 * (sd/(Math.sqrt(n))));
var high_99 = mean – (-1*(z_99 * (sd/(Math.sqrt(n)))));
//output values
document.getElementById(‘low90’).innerHTML = low_90.toFixed(3);
document.getElementById(‘high90’).innerHTML = high_90.toFixed(3);
document.getElementById(‘low95’).innerHTML = low_95.toFixed(3);
document.getElementById(‘high95’).innerHTML = high_95.toFixed(3);
document.getElementById(‘low99’).innerHTML = low_99.toFixed(3);
document.getElementById(‘high99’).innerHTML = high_99.toFixed(3);
}