You can probably model this with a Poisson Distribution although it would be better to have more data.

In the real world, you can't let things stay broken just to get more data.

http://en.wikipedia.org/wiki/Poisson_distribution

There is a formula on the Wikipedia page for 95% confidence limit calculations.

In the real world, you can't let things stay broken just to get more data.

http://en.wikipedia.org/wi

There is a formula on the Wikipedia page for 95% confidence limit calculations.