Chy 17.True/false: The standard error of the mean is smaller when N = 20 than when N 10 True Ch10 8. What is the effect of sample size on the width of a confidence interval? The larger the sample size, the smaller the width. 17. Heights for teenage boys and girls were calculated. The mean height for the sample of 12 boys was 174 cm and the variance was 62. For the sample of 12 girls, the mean was 166 cm and the variance was 65. Assuming equal variances and normal distributions in the population, (a) What is the 95% confidence interval on the difference between population means? (b) What is the 99% confidence interval on the difference between population means? (c) Do you think it is very unlikely that the mean difference in the population is about 5