So, I received five answers which seem credible to me, the answers of GregInAustin, Tiktaalik, Loss Leader, gabeygoat and DuvalHMFIC. Out of these five answers, four are numerically correct, and one (the one by GregInAustin) was numerically incorrect.
The {correct answer} rate for credible answers in this test is therefore equal to 80%, which is much higher than the "hit rate" from chance alone (about 25%).
In the previous test (
http://www.internationalskeptics.com/forums/showthread.php?p=8607740#post8607740 ), I found
a {correct answer} rate equal to 100% for credible answers. In this previous test, I also obtained a {correct answer} rate (for all answers, credible or not) equal to 23.1% (the global hit rate is equal to 22.7% in this second test). These results (100% → 80%, and 23.1 → 22.7%) suggest a small decline in quality, from the first test on this forum to this second one. However, the number of valid numerical answers was much higher in this test (22, compared to 13 in the first test).
It may be interesting to introduce a credibility threshold, equal to CR=5, for exemple. Then, GregInAustin's answer (CR=2) is eliminated, and I obtain 3+4 = 7 ("strongly") credible answers for the two tests (on this forum, so far), all of which are numerically correct.
The probability for this is equal to p = (1/4)7 = 6.10 x 10-5 (assuming a 25% probability of answering correctly, for each answer).