A
confidence interval for a difference between means
is a range of values that is likely to contain the true difference between two population means with a certain level of confidence.
The formula to calculate the confidence interval is:
Confidence interval = (
x
1
–
x
2
) +/- t*√((s
p
2
/n
1
) + (s
p
2
/n
2
))
where:
x
1
,
x
2
: sample 1 mean, sample 2 mean
t: the t-critical value based on the confidence level
s
p
2
: pooled variance
n
1
, n
2
: sample 1 size, sample 2 size
To find a confidence interval for a difference between two means, simply fill in the boxes below and then click the “Calculate” button.
x
1
(sample 1 mean)
s
1
(sample 1 standard deviation)
n
1
(sample 1 size)
x
2
(sample 2 mean)
s
2
(sample 2 standard deviation)
n
2
(sample 2 size)
Confidence level
95
% C.I. = [
-2.0049
,
3.6049
]
You can be
95
% confident that the interval [
-2.0049
,
3.6049
] contains the true difference between the population means μ
1
and μ
2
.