Homework 2

Practice problems

1. Vu and Harrington exercise 4.1. Additionally:

   5. Compute an interval estimate for the mean BGC of nests and interpret the interval in context.
   6. Supposing a sample of 30 nests returned exactly the same summary statistics, recompute your interval in (e). Is the margin of error smaller or larger?

Note: this problem can be done entirely by hand. Alternatively, if you wish to use R, you can input the given summary statistics directly – for example, bcg.mean <- 0.6052 – and perform the calculations as in the lab activity.

Solution

# input summary statistics directly for this problem

# part a: point estimate for population mean is sample mean

# part b: point estimate for population sd is sample sd

# part c: deviation of 0.63, relative to sd

# part d: standard error for estimate in (a)

# part e: interval for the population mean

# part f: repeat e, but suppose only 30 nests were measured

3. [your answer here]
4. [your answer here]
5. [your answer here]

2. The brfss dataset contains a measurement of body weight, weight, as well as a variable, wtdesire, that is the desired weight reported by respondents.

   1. Compute point estimates and standard errors for the actual and desired body weight of U.S. adults.
   2. Report your estimates in (a) following conventional style.
   3. Do your estimates suggest that the average U.S. adult would prefer to lose or gain weight?
   4. Compute an interval estimate for the mean difference between actual and desired weight. Interpret the interval in context.

Solution

# load dataset and inspect

## part a: point and interval estimates for...

# actual body weight

# desired body weight

## part d: interval estimate for mean difference

2. [your answer here]
3. [your answer here]
4. [your answer here]