One trick you can use to estimate how much belief you should put into a claim is to ask yourself what things if true would make you believe the claim. In other words, what evidence, presented together, would be convincing to you?
Once you have your list of “convincing evidence”, estimate a probability for each item. This is just your current best guess. You can and should change these estimates based on new information. If you’re particularly uncertain about an item, you could even do this overall exercise for that item (i.e. look at the sub-evidence that would required for it, estimate those probabilities, etc.).
Once you have the probabilities, multiply them together to estimate a probability for the overall claim.
Let’s use the claim “COVID-19 is a Chinese bioweapon that escaped (or was released) from a Wuhan lab” as an example. This sounds like a conspiracy theory, so my initial reaction is one of disbelief, but I have no rigorous basis for belief. My gut reaction could be wrong. So, let’s do the analysis and see.
My “Convincing Evidence” with Probability Estimates:
Final calculation:
\[90\% \times 50\% \times 50\% \times 99\% \times 10\% \approx 2.2\%\]My final estimate would thus be 2.2% (pretty unlikely but not impossible).