Question

Many birds are injured or killed by flying into windows. It appears that birds don't see windows. Can tilting windows down so that they reflect earth rather than sky reduce bird strikes?

Researchers placed six windows at the edge of a woods: two vertical, two tilted 20 degrees, and two tilted 40 degrees. During the next four months, there were 53 bird strikes, 31 on the vertical windows, 14 on the 20‑degree windows, and 8 on the 40‑degree windows.

Calculate the expected counts in each of the three conditions and compute the chi‑square statistic.

The expected counts for each condition (vertical, downward 20 degree, and downward 40 degree respectively) will be

a) 17.67,17.67,17.67

b) 10.33,17.67, 8.83

c) 8.83,10.33, 5.02

d) 16.64,16.64,16.64

The chi‑square statistic is

a) ?2=16.11

b) ?2=18.38

c) ?2=19.58

d) ?2=15.09

Answer 1

Solution:

The expected counts for each condition will be

Correct Answer: a) 17.67,17.67,17.67

Explanation:

The calculation table for expected count is given as below:

Window	Observed (O)	Expected (E)
Vertical	31	53/3 = 17.67
20-degree	14	53/3 = 17.67
40-degree	8	53/3 = 17.67
Total	53	53

Test statistic formula is given as below:

Chi square = ∑[(O – E)^2/E]

Where, O is observed frequencies and E is expected frequencies.

Calculation table is given as below:

Window	O	E	(O - E)^2	(O - E)^2/E
Vertical	31	17.67	177.7777778	10.06
20-degree	14	17.67	13.44444444	0.76
40-degree	8	17.67	93.44444444	5.29
Total	53	53		16.11

Chi square = ∑[(O – E)^2/E] = 16.11

Correct Answer: a) ?2=16.11