Crossbill finches have beaks that overlap with the top beak to one side or the other of the lower beak. Most populations have 50:50 ratios of "right-handed" and "left-handed" beaks, and the handedness of the beaks is thought to be randomly determined, so we expect to see equal numbers of right-handed and left-handed finches. Consider a survey of 140 crossbill finches, which reveals 84 with right beaks and 56 with left beaks. What is the P-value of a two-sided binomial test using the normal distribution to approximate the binomial?

Question

Quizplus · Accepted Answer

The P-value is calculated using the normal approximation to the binomial distribution. The observed proportion is 84/140 = 0.6, and the expected proportion is 0.5. The standard deviation is sqrt(0.5*0.5/140). The z-score is (0.6-0.5)/standard deviation, and the two-tailed P-value corresponds to this z-score, which is approximately 0.023.

Crossbill Finches Have Beaks That Overlap with the Top Beak