Let me say right off the bat that the number of contracts I’ve had where people wanted me to tell them what to do I can count on one hand – and I’ve been in business 30 years. Generally, whether it is an executive in an organization where I’m an employee or a client for my consulting services, people don’t want me to tell them what to do,
Hey, you should do a repeated measures ANOVA.
Nope, they want me to DO it. It’s funny how often I find myself doing the same procedures for vastly different organizations, everywhere from the middle of Missouri to downtown Los Angeles to American Indian reservations in North Dakota to (soon) Santiago, Chile.
There are also those procedures I only use once in a great while, but that’s the topic of another post. Here are a couple of my go-to procedures.
Fisher’s Exact Test
PROC FREQ DATA = install ;
TABLES rural*install / CHISQ ;
is an example of how you do it in SAS for everything from testing whether urban school districts have significantly more bureaucratic barriers to using educational technology than rural districts (they do) to whether mortality rates are lower in a specialized unit in a hospital than for patients with the same diagnosis in a standard unit.
Confidence Limits for the Mean
Working with small samples in rural communities, I often don’t have the luxury of a control group. I know this makes me sound like a terrible researcher and that I never read a quantitative methods or experimental design textbook. However, let me give you an example of the types of conversations I have all of the time.
Me: I’d like to use your program as a control group. I’ll come in and test all of your students and then two months later, I’ll test them all again.
Principal/ Superintendent/ Program Director: You mean you want me to take up two periods of class / counseling time for your tests?
Them: You wouldn’t actually be giving our students any services or educational program, you’d just be taking two hours from all of our students.
Me: Yes, and then I’ll compare their results to those of the students who do get services.
Them: What do our students get out of it?
You can see where this conversation is going. One solution might be to pay all of the students some amount to stay after school or come in for an extra counseling period or whatever is being compared, so they aren’t missing out on services to take the test. However, Institutional Review Boards are cautious about having substantial incentives because then they feel very low income might be coerced into participating – for some of the people on our research, $10 is a lot of money.
The result is that I don’t always have a control group, but all is not lost. Being smarter than I look (yes, really), I often use standardized measures for which there is a lot of research documenting the mean and I can do a one-sample test.
proc means data=cesd_score alpha=.05 clm mean std ;
var cesdtotal ;
This will give me the 95% confidence interval for the mean and I can see if my sample is significantly different from the mean . For example, with a sample of 18 children from an American Indian reservation, the mean score on the CESD – C, a measure of depression, the mean score was 21. The cutoff for considering the respondent as showing depressive symptoms is 15. With a confidence interval from 15.6 to 26.4 I can say that there is a greater than 95% probability that the population mean fits the cutoff for depressive symptoms. Notice that the lower confidence limit still is above the screening cutoff point of 15.
There is an interesting question related to this specific study, but it will have to wait for tomorrow since I have to head to the airport in a few hours. This week, I’m heading to Missouri. If you want to meet up and talk statistics, video games or just drink beer, let me know.
Play Aztech: The Story Begins – free for your iPad in the app store, in Spanish and English. The first in our series of bilingual games teaching math and history.