**Bayesian Assurance: The True Probability of Success**

Bayesian statistical methods continue to gain in popularity with researchers thanks to their ability to integrate prior information,

- Assurance is a calculation that integrates a number of parameters surrounding a trial or drug development that provides an indication of the "true probability of success of a trial". In frequentist terms, this is akin to providing a statistically significant result.

- Assurance can be calculated as the expected statistical power based on a prior distribution

of the unknown parameters related to the effect size. This provides a "Bayesian Power" estimate which can be used as an alternative to the traditional power analysis used in most intervention research.

- Assurance may also be considered as a Bayesian formalization of a sensitivity analysis

- To calculate Bayesian Assurance, priors have to be elicited from expert opinions and/or existing data and then integrated into frameworks such as the Sheffield Elicitation Framework (SHELF).
- Through the elicitation
process all relevant data is summarized, reviewed and implicitly weighted. - Based on the
experts responses and weighting, biostatisticians can develop a probability distribution that demonstrates both current knowledge and uncertainty of the current milestone move.

- Assurance (probability of success) is the power averaged over all plausible values by assigning prior to one or more parameters, providing a summary statistic for the effect of parameter uncertainty. This can highlight unforeseen problems and lead to better decision making or appropriate reviews.

**Bayesian Assurance - The True Probability of Success**Our clients using nQuery Bayes and a framework such as SHELF have reported auser friendly method to use Assurance (A) in their decision making across many levels, ultimately allowing for improved study, risk and financial decisions. This is thanks to having a greater understanding of the true probability of success for a given scenario.

**Identify Study Design Threats & Opportunities****-**Bayesian Techniques such as Prior Elicitation provides a systematic approach to reduce the analysis gap between completed studies and planned studies when there is a lack of reliable evidence or scientific consensus.**-**Examining experts prior distribution may often reveal concerning aspects of the study design that was previously overlooked.**-**The elicited prior distribution can be used to assess various study designs. These can ultimately be influential in the appropriate ‘go’ or ‘no go’ decision.**-**The elicitation process highlights not only the rationale for believing in the likely effect of thedrug, but the gaps in knowledge and/or sources of uncertainty

**Communicate Complex Findings to Non-Statisticians**The prior elicitation process is methodically and scientifically-driven. It enables a more vigorous review of data and decision making.However through nQuery Bayes, researchersare presented a Bayesian Assurance calculation that can be communicated to non-statisticians, including internal governance boards, in an easy to understand way.

A more robust understanding of risks and insights means these can be formally acknowledged and plans made to mitigate these risks to reduce costs and thus reduce the likelihood of failure.

Being able to formally capture internal and expert opinion, integrate existing data and identify obstacles in the study protocol, teams can provide boards with formally appropriate estimates of the probability of trial success as well as robust plans for interim decision rules where appropriate, enabling better portfolio and company-wide decision making.

**Bayesian Assurance is a vital contextual tool in the biostatisticians planning toolbox. It places uncertainty at the heart of sample size determination. nQuery Bayes presents an easy to use formal method of discovering the true probability of success.**

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**Benefits of Sensitivity Analysis:**What does the researcher gain by conducting a sensitivity analysis?**Why isn't Sensitivity Analysis formalized:**Why does sensitivity analysis still lack the type of formalized rules and grounding to make it a routine part of sample size determination in every field?**How Bayesian Assurance works:**Using Bayesian Assurance provides key contextual information on what is likely to happen over the total range possible values rather than the small number of fixed points used in a sensitivity analysis**Elicitation & SHELF:**How expert opinion is elicited and then how to integrate these opinions with each other plus prior data using the Sheffield Elicitation Framework (SHELF)**Why use in both Frequentist or Bayesian analysis:**How and why these methods can be used for studies which will use Frequentist or Bayesian methods in their final analysis