Question

“Domestic cats kill many more wild birds in the United States than scientists thought,” states a recent article.¹ Researchers used a sample of n=140 households in the US with cats to estimate that 35% of household cats in the US hunt outdoors.

(a) Find a 95% confidence interval for the proportion of household cats in the US that hunt outdoors.

Answer 1

a) Z score for 95% confidence interval = Z_0.025 = 1.96

p = 0.35

n = 140

Confidence interval = (p + Z_0.025 * sqrt(p * (1 - p) / n))

                                = (0.35 + 1.96 * sqrt(0.35 * 0.65 / 140))

                                = (0.35 + 0.079)

                                = (0.271 , 0.429)