Confidence Interval Calculator
A normal-approximation interval is sample mean plus or minus z times standard error.
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How it works
A normal-approximation interval is sample mean plus or minus z times standard error.
Worked example
At 95% confidence, a sample mean of 100 with SD 15 and n=100 has margin about 2.94.
Keep in mind
Small samples or nonnormal data may need another method.