Need Statistical Help!

[seped]

Not really, this seems like a perfect example of the central limit theory, many independent random variables drawing from an unknown distribution will be approximately normally distributed.

That aside, do we have any strong assumption the drop rates aren't independent and normal?

Also, I goofed in my above post, you want +/- 2* the std error, not std deviation, it's just stddev divided by sqrt(sample size). For example in ruby..

irb(main):001:0> require 'statsample'
=> true
irb(main):002:0> test = 100.times.map { rand < 0.1 ? 1 : 0 }
=> [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 1, 0, 0, 0, 0,
 0, 0, 0, 0, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0]
irb(main):004:0> test = test.to_scale
=> Vector(type:scale, n:100)[0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,0,0,0,0,0,0,1,1,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,0,0,1,0,0,0,0,1,0,0,0,0,1,1,0,0,0,0,0,0,0,0,0,0,0,0,0,1,0]
irb(main):005:0> test.mean
=> 0.11
irb(main):006:0> test.sd
=> 0.3144660377352203
irb(main):007:0> t_1 = Statsample::Test::T::OneSample.new(test, {:u => test.mean})
irb(main):009:0> puts t_1.summary
= One Sample T Test
  Sample mean: 0.1100 | Sample sd: 0.3145 | se : 0.0314
  Population mean: 0.1100
  t(99) = 0.0000, p=1.0000 (both tails)
  CI(95%): -0.0624 - 0.0624
=> nil
irb(main):010:0>

You can see that in this sample we'd report that the drop rate was 11%, plus or minus 6% which is dead on with the underlying mean of 10%.