Case study

Chapter 8
Interval Estimation

Case Problem 1: Young Professional Magazine

1. Descriptive Statistics for the quantitative variables follow:

Variable N Mean SE Mean StDev Minimum Maximum Skewness
Age 410 30.112 0.199 4.024 19.000 42.000 -0.03

Investments 410 28538 781 15811 0.000 133400 1.71

Transactions 410 5.973 0.153 3.101 0.000 21.000 1.21

Household Income 410 74460 1720 34818 16200 322500 2.01

Descriptive statistics for the qualitative variables follow: Gender Male: 229 Proportion male: .5585

Plan R.E. purchase Yes: 181 Proportion yes: .4415

Broadband access Yes: 256 Proportion yes: .6244

Have Children Yes: 219 Proportion yes: .5341

2. 95% Confidence Intervals

Variable N Mean StDev SE Mean 95% CI Age 410 30.1122 4.0240 0.1987 (29.7215, 30.5029)

Variable N Mean StDev SE Mean 95% CI Household Income 410 74459.5 34818.2 1719.5 (71079.3, 77839.8)

We can conclude with 95% confidence that the mean age of subscribers to Young Professional is between 29.72 and 30.50 years of age. And, we can conclude with 95% confidence that the mean household income of subscribers is between $71,079 and $77,840.

3. 95% Confidence Intervals

Variable X N Sample p 95% CI
Broadband Access 256 410 0.624390 (0.577514, 0.671266)

Variable X N Sample p 95% CI
Have Children? 219 410 0.534146 (0.485861, 0.582431)

We can conclude with 95% confidence that the proportion of subscribers with broadband access is between 57.75% and 67.13% and that the proportion of subscribers with children is between 48.59% and 58.24%.

4. Young Professional should be a good advertising outlet for online brokers. We see that most of the subscribers have financial investments