Here are the answers to exam 1. For some of the questions, I have provided explanatory material in regular type, and the answer in **bold**; all you need to write down is the answer. If you don't understand why your answer was wrong, you may e-mail me, talk to me before or after class, or set up a time to talk to me in my office. The exam was worth 15 points, so each question was worth 0.75 points.

**1. ** Two nominal variables, Lignextra vs. control, snoring vs. not snoring; total sample size is 90; **Fisher's exact test of independence**.

**2. ** Because the null hypothesis is true, **the probability of getting a significant result is equal to the significance level, or alpha**. Because we're using a significance level of 0.05 in this class, all you needed to write for full credit was **0.05** or **5%**.

**3. ** Two nominal variables, kind of cat, adopted vs. not adopted; total sample size is more than 1000; **chi-square test of independence** or **G-test of independence**.

**4. ** **An exact test is better when the sample size is small, because the P-value is more accurate than for a chi-square or G-test. We use the chi-square or G-test when the sample size is large, because the calculations for an exact test are difficult even for a computer, and because all three tests give about the same P-value when sample sizes are large. **.

**5. ** Because 42.3% of the area is cars, ** The null hypothesis is that 42.3% of the poops will be on cars.**. There is one nominal variable, car vs. asphalt, and the total sample size is less than 1000, so the test is **exact test of goodness-of-fit**.

**6. ** ** Hematocrit: measurement **(because there are more than 5 values);**Time to ride 100 miles: measurement**.

**7. ** Two nominal variables, dimly lit vs. dark, noon vs. midnight; total sample size is greater than 1000 (750+800); **chi-square test of independence** or **G-test of independence**.

**8. ** **alpha: 0.05 **(also known as significance level)

**beta: 0.20** or **power: 0.80 **. You got points off for putting down both beta and power, because power equals one minus beta, you only need to pick one.

**Effect size: 15 percent fewer deaths**

**9. ** ** Make alpha larger; make beta larger (or power smaller); make effect size larger.**.

**10. ** **Species of slug: nominal
Water content: nominal ** (because just two values, 15 and 30%.

**11. ** Three nominal variables, kind of corn (sweet vs. yellow dent), strain of borer (E or Z), location; ** Cochran-Mantel-Haenszel test**.

**12. ** **0.003 is the probability of getting a difference in mean milk production between grass-fed and hay-fed goats of 0.7 liters per day, or more, by chance if the null is true**.

**13. ** Three nominal variables, near vs. far from cedar tree, rust spot vs. no rust spot, orchard; ** Cochran-Mantel-Haenszel test**.

**14. ** **Time that turtle pokes its head up: measurement
walking speed: measurementeaten vs. safe: nominal **.

**15. ** **Total number of salamanders: measurement
soil pH: measurement
number of dead logs: measurement
white oak vs. non-white oak leaf: nominal
human activity scale: measurement
amount of light: ranked **. Whether you consider the quadrats to be a nominal variable is a gray area that we'll talk about later in the semester; you didn't get points off for omitting or including it. You did get points off if you considered the quadrats to be a measurement variable.

**16. ** Two nominal variables, *Mpi* genotype, young vs. adult; total sample size greater than 1000: **chi-square test of independence** or **G-test of independence**. These are the actual numbers from a study I did for my Ph.D. dissertation; the results were so boring that their only use is for exam questions.

**17. ** One nominal variable, raccoon vs. feces vs. cheese; total sample size less than 1000: **exact test of goodness-of-fit **.

**18. ** **Number of fireflies, measurement
sand particle size: measurement
percent of area that is bare sand: measurement ** (because it's the percentage of the area, you're not counting individual grains and sorting them into sand vs. something else).

**19. ** Two nominal variables, HTPAP genotype, cancer vs. no cancer; total sample size less than 1000: ** Fisher's exact test of independence**.

**20. ** **Behavior: measurement
Sugar amount: ranked
Age: measurement ** If you explicitly said you measured the age in years, I accepted "nominal," since second graders might all be either 7 or 8. But any sensible biologist would measure the age of such young children in months or days, which would be a measurement variable.