Agresti-Coull add-4 CI for a binomial proportion, based on adding 2 successes and 2 failures before computing the Wald CI. The CI is truncated, when it overshoots the boundary

1 | ```
add4ci(x, n, conf.level)
``` |

`x` |
number of successes |

`n` |
number of trials |

`conf.level` |
confidence coefficient |

A list with class '"htest"' containing the following components:

`conf.int ` |
The confidence intervall for the proportion |

`estimate ` |
The estimator for the proportion |

Agresti, A., Coull, B. (1998) Approximate is better than exact for
interval estimation of binomial proportions. *The American
Statistician* 52, 119–126.

Agresti, A., Caffo, B.(2000) Simple and effective confidence intervals
for proportions and difference of proportions result from adding two
successes and two failures. *The American Statistician* 54 (4), 280–288.

1 | ```
add4ci(x = 15, n = 112, conf.level = 0.95)
``` |

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