# How to combine estimated confidence intervals

I have sampled a set of expert on their 90% CI for a set of questions. How can I combine their answers? How confident can I be in the result?

|---------------------------------------|
|     Question 1                        |
|---------------------------------------|
|         | Lower bound  | Upper bound  |
|         | (95% chance  | (95% chance  |
|         |  value is    |  value is    |
| Expert  |  higher)     |  lower)      |
|---------|--------------|--------------|
|  A      | 130          |  627         |
|  B      | 202          |  584         |
|  C      | 186          |  648         |


Ideally, I'd like to understand what my lower and upper bounds are likely to be and how confident I should be in these bounds.

• Confidence intervals do not tell you how confident you could be about the results, neither they tell you about the chance of value being higher or lower (see other questions tagged as confidence-interval, e.g. stats.stackexchange.com/q/26450/35989). What exactly do you want to achieve? – Tim Jan 17 '18 at 18:23
• Say, for example, I asked 5 astronomers what the diameter of the moon was (without looking it up). They may not know off the top of their heads, but they know it's almost certainly larger than X and smaller than Y. Can I take those 5 estimates and combine them to a single estimate that is superior than any of the 5 individually? – PaulH Jan 17 '18 at 18:54
• You can't combine these. The Experts are giving Bayesian credible intervals based on their priors. The priors don't have any frequentist properties. They can't be averaged to produce meaningful results. It is a conflagration of qualitative and quantitative results with no actual data to update the priors. – AdamO Jan 17 '18 at 19:55