| name | pra-bayesian-risk |
| description | Compute and update the probability of a risk event from root causes, and turn risk probabilities into project cost distributions, using the PRA package. Use when a user has a risk register with root-cause probabilities and wants a prior risk probability, a Bayesian update after observing causes, or a cost-impact distribution.
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When to use
Best when you have identifiable root causes with estimated probabilities and
want to update estimates as the project progresses (i.e. a risk register). For
task-level distributions and total project cost/schedule, prefer Monte Carlo
(pra-monte-carlo). The two combine: estimate risk probabilities here, then
feed cost impacts into a cost distribution.
Prior and posterior risk probability
risk_prob_tool(cause_probs_json, risks_given_causes_json, risks_given_not_causes_json) computes P(R) by the law of total probability
over independent root causes. All three arrays are the same length:
cause_probs_json: P(cause present), e.g. [0.3, 0.2]risks_given_causes_json: P(Risk | Cause), e.g. [0.8, 0.6]risks_given_not_causes_json: P(Risk | not Cause), e.g. [0.2, 0.4]
risk_post_prob_tool(..., observed_causes_json) updates P(R) after observing
cause states. observed_causes_json uses 1 (occurred), 0 (did not occur),
null (still unknown), e.g. [1, null].
Cost distributions
cost_pdf_tool(num_sims, risk_probs_json, means_given_risks_json, sds_given_risks_json, base_cost) — prior cost distribution. Each simulation
draws whether each risk occurs, then samples its cost impact.cost_post_pdf_tool(num_sims, observed_risks_json, means_given_risks_json, sds_given_risks_json, base_cost) — posterior after observing which risks
occurred (observed_risks_json uses true/false/null).
Parameters: means_given_risks_json / sds_given_risks_json give the mean and
SD of the additional cost if a risk occurs (one per risk); base_cost is the
baseline before any risk impacts.
Workflow
risk_prob_tool → cost_pdf_tool → [observe causes/risks] →
risk_post_prob_tool → cost_post_pdf_tool.
References
- NASA Risk-Informed Decision Making Handbook (SP-2010-576).
- NASA Bayesian Schedule and Cost Risk Analysis.
