# Rand does not return expected confidence interval
**URL:** https://discourse.julialang.org/t/rand-does-not-return-expected-confidence-interval/123053
**Category:** Optimization (Mathematical)
**Created:** [November 25, 2024, 6:42pm UTC](https://discourse.julialang.org/t/rand-does-not-return-expected-confidence-interval/123053 "2024-11-25T18:42:10Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@Trylmand](https://discourse.julialang.org/u/Trylmand)
#### Post date: [November 25, 2024, 6:42pm UTC](https://discourse.julialang.org/t/rand-does-not-return-expected-confidence-interval/123053/1 "2024-11-25T18:42:10Z")
Dear all,
Testing Rand() on MC algorithm for estimating integral of Sine from 0 to Pi,
only returns 50% of the expected confidence interval.
Can anybody see, where my code breaks?
n = 1000
in\_ci = 0
for i in 1:500
sin\_arr = map(x → sin(x), pi_rand(n))
lower = pi_mean(sin\_arr) - 1.96_std(sin\_arr)/sqrt(n)
upper = pi_mean(sin\_arr) + 1.96\*std(sin\_arr)/sqrt(n)
if (lower \<= 2) && (upper \>= 2)
in\_ci += 1
end
end
println("For n = ", n, " share of estimates in CI.: ", in\_ci/500)
Result.:
For n = 1000 share of estimates in CI.: 0.468
---
### Author:  [@DanielVandH](https://discourse.julialang.org/u/DanielVandH)
#### Post date: [November 25, 2024, 6:53pm UTC](https://discourse.julialang.org/t/rand-does-not-return-expected-confidence-interval/123053/2 "2024-11-25T18:53:06Z")
Welcome to the forum! Note that you can wrap your code in triple backticks (`) to properly quote your code.
I think you will get the correct result if you also multiply your standard error by `pi`?
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### Author:  [@Trylmand](https://discourse.julialang.org/u/Trylmand)
#### Post date: [November 25, 2024, 7:02pm UTC](https://discourse.julialang.org/t/rand-does-not-return-expected-confidence-interval/123053/3 "2024-11-25T19:02:32Z")
Thx, got blind staring at the code 🙂