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Statistical function
CONFIDENCE.NORM
Returns the margin of a confidence interval for a population mean.
Rarely usedDifficulty 1500 · AdvancedUsage rank #391 of 520
When to use it
The half-width of a confidence interval for a mean when the population standard deviation is known (or the sample is large). Add and subtract it from the sample mean.
The shape of it
- Syntax
=CONFIDENCE.NORM(alpha, standard_dev, size)
Worked examples
95% interval
=CONFIDENCE.NORM(0.05,2.5,50) → 0.692951912
95% interval, sd 2.5, 50 observations.
Larger sample
=CONFIDENCE.NORM(0.05,15,100) → 2.939945977
Mean ± 2.94 with sd 15 and n = 100.
99% interval
=CONFIDENCE.NORM(0.01,15,100) → 3.863743937
99% needs a wider interval.
Worth knowing
- Alpha is 1 minus the confidence level: 0.05 for 95%.
- Use CONFIDENCE.T for small samples where the sd is estimated from the data.
- The interval is mean ± the result.
Where it goes wrong
- #NUM! when alpha is outside 0 to 1, sd is not positive, or size is less than 1.
- Assumes a normal sampling distribution; very skewed data with small n breaks that.
Related
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