find_beta_params {adaptr} | R Documentation |

## Find beta distribution parameters from thresholds

### Description

Helper function to find a beta distribution with parameters corresponding
to the fewest possible patients with events/non-events and a specified event
proportion. Used in the **Advanced example** vignette
(`vignette("Advanced-example", "adaptr")`

) to derive `beta`

prior
distributions for use in *beta-binomial conjugate models*, based on a belief
that the true event probability lies within a specified percentile-based
interval (defaults to `95%`

). May similarly be used by users to derive other
`beta`

priors.

### Usage

```
find_beta_params(
theta = NULL,
boundary_target = NULL,
boundary = "lower",
interval_width = 0.95,
n_dec = 0,
max_n = 10000
)
```

### Arguments

`theta` |
single numeric |

`boundary_target` |
single numeric |

`boundary` |
single character string, either |

`interval_width` |
width of the credible interval whose lower/upper
boundary should be used (see |

`n_dec` |
single non-negative integer; the returned parameters are rounded
to this number of decimals. Defaults to |

`max_n` |
single integer |

### Value

A single-row `data.frame`

with five columns: the two shape parameters
of the beta distribution (`alpha`

, `beta`

), rounded according to `n_dec`

,
and the actual lower and upper boundaries of the interval and the median
(with appropriate names, e.g. `p2.5`

, `p50`

, and `p97.5`

for a
`95%`

interval), when using those rounded values.

*adaptr*version 1.4.0 Index]