confidence level 80% 90% 95% 99% 99.9% area to left .90 .95 975 .995 .9995 area to right 10 .05 025 005 .0005 critical value z 1.282 1.645 1.960 2.576 3.291 1 A survey of 8,000 American households found that 27.3% of the households in the sample owned a pet cat. Use this sample information to form a 90% confidence interval to estimate the proportion of all American households that owned a pet cat