Analysis of information sources in references of the Wikipedia article "Orders of magnitude (probability)" in English language version.
Triplet or higher order birth rate: 137.0 per 100,000 live births
Twin birth rate: 33.2 per 1,000 live births
1 in 258,890,850
2.0 0.02275 ... 3.0 0.00134
15.87% of all instances fall to the left of —1 standard deviation
With 1.4 million hours MTBF