Description

Statistics Lab Worksheet
PPOL 552-01 Research Methods

PART 2. Let’s use the sample data to make some confidence interval estimates:

Example A:

** estimate a 95% confidence interval for mean age

ci means age, level (95)

<COPY AND PASTE STATA COMMAND AND OUTPUT HERE>

Example A Interpretation:

·         Based on this sample, I am ___95___% confident that the population mean age is between _______52.3____years_____ and ________54.7 years________ .

·         Being _95_____% confident” means that _95__% of the possible samples would produce confidence intervals that contain the actual population mean. It also means that, due to sampling error, there is a ____5__%  chance of drawing a sample and estimating a confidence interval from it that doesn’t contain the population mean.

Example B Interpretation:

** estimate 99% confidence interval for a categorical variable’s proportions

proportion educ, level(99)

<COPY AND PASTE STATA COMMAND AND OUTPUT HERE>

Example B Interpretation:

·         Based on this sample, I am ___99___% confident that between ___11.2___% and __16.9____% of the population has a graduate degree. I am also __99____% confident that between ___10.8___% and __16.3____% of the population has a two-year associate degree.

·         Since these two confidence intervals DO  overlap each other, I
CANNOT be confident about which of these two groups is likely to be the largest in the population. They could even be exactly equal in size, even though the estimates are not equal.

·         I am also __99____% confident that a third group, those whose highest degree is a bachelor’s degree, is larger than either of the two groups discussed above because its confidence interval (__18.0____% to __24.7____%) DOES NOT overlap either of the other two confidence intervals.

Example C:

** estimate proportion intervals for values of another categorical variable

proportion educ, over(ownhome) level(95)

<COPY AND PASTE STATA COMMAND AND OUTPUT HERE>

Example C Interpretation:

·         Based on this sample, I am __95____% confident that between __15.0____% and ___20.7___% of those who own a home in the population have graduate degrees.

·         I am also ___95___% confident that between ___3.1___% and ___8.3___% of those who rent in the population have graduate degrees.

·         Since these two intervals DO NOT overlap, I am also _95_____% confident that a(n)
EQUAL / LARGER / SMALLER proportion of home owners have graduate degrees compared to renters.

·         This finding MIGHT  suggest that the amount of education and home ownership have a pattern of association in the population. (Further statistical testing is needed to assess this possibility, which we will investigate in Statistics Lab 2).

Example D:

** estimate proportion intervals for values of another categorical variable

proportion WEED4, over(mstatus) level(95)

<COPY AND PASTE STATA COMMAND AND OUTPUT HERE>

Example D Interpretation:

·         Based on this sample, I am ______% confident that between ______% and ______% of those who are married in the population have smoked marijuana.

·         I am also ______% confident that between ______% and ______% of those who are divorced in the population have smoked marijuana.

·         Since these two intervals DO / DO NOT overlap, I am also ______% confident that a(n)
EQUAL / LARGER / SMALLER proportion of married individuals have smoked marijuana compared to individuals who are divorced.

·         This finding MIGHT / MIGHT NOT suggest that martial status and using marijuana have a pattern of association in the population. (Further statistical testing is needed to assess this possibility, which we will investigate in Statistics Lab 2).

PART 3. Prepare some inferences of your own using the commands above.

For Part 3 of the worksheet, investigate these data further using the summary statistics commands. Your goal should be to develop three new and interesting findings about the population of American adults (so you may not use the example findings in this document). You may use any of the statistical procedures we learned as shown in step 2 above, but your findings must include at least two confidence interval estimates.

In writing up your results, you should include the Stata command you ran and its results, clearly highlighting the relevant information in those results. Then describe the results concisely, and provide a clear interpretation of the results in plain language. You should consult the examples we completed in class in Part 2, but must write your results in your own words. Be sure to focus on what you’ve learned about the POPULATION, not the sample—remember, that is the goal of statistical inference.