### Final exam study guide: Practice exam 2

Here are some practice questions for the final exam. There are 30 questions, just like the real final, so I suggest you give yourself two hours to answer them. When you're done, you can see the answers.

1. The repeated stress of running sometimes causes stress fractures in the tibia (lower leg). Often just one tibia gets a stress fracture, and you want to know whether the tibia that gets fractured had different bone mineral density than the uninjured tibia of the same person. You measure the bone mineral density in each of the two tibias in 100 people who are about to start running. Six months later, you find that 12 runners have a stress fracture in one leg. You look up the bone mineral density values for the fractured and unfractured tibia in each of the 12 people. Which test should you use?
2. You want to know whether aspirin taken during pregnancy has an effect on the size of offspring. You ask 1072 new mothers whether they took aspirin during the first three months of their pregnancy. The average weight of newborn babies of mothers who took aspirin is 103 grams less than babies of mothers who didn't take aspirin. You do the appropriate statistical test and get P=0.07. What is this the probability of?
3. You want to know what affects the breakdown of fructose at high temperatures (due to caramelization and Maillard reactions) in apples. You bake 8 Winesap apples, 8 Rome Beauty apples, 8 Jonathan apples, and 8 Granny Smith apples for 90 minutes at 180 C, and you bake another set of 8 apples of each variety for 90 minutes at 200 C. You measure the amount of fructose (in milligrams of fructose per gram of baked apple) in each apple. Which test should you use?
4. Because many lichens can fix atmospheric nitrogen, lichens falling from tree branches to the forest floor are an important part of the ecosystem of old-growth forests. You want to study what affects the colonization of young trees by lichen, so you find a forest that had a severe fire 100 years ago and therefore has a mixture of a few 600-year-old trees (that survived the fire) and a large number of trees that are less than 100 years old. You randomly choose 20 of the younger trees, put a box under each one for a week, and then weigh the amount of lichen litter that falls into the box. You also determine the age of each tree (by counting the rings), the diameter, the height, and the distance to the nearest 600-year-old tree. Which test should you use?
5. You have created a mouse model of hypercholesteremia by knocking out the LDLR gene, and you want to know whether this affects atherosclerosis ("hardening of the arteries"). You have 12 LDLR-/LDLR- mice and 12 LDLR+/+ mice. You feed the mice a high cholesterol diet for 20 weeks, then prepare 4 cross-sections from random parts of the aorta for each mouse. On each cross-section, you measure the area of atherosclerosis lesion. Which test should you use?
6. People who live in New Guinea have a diet based on sweet potatoes, which are low in nitrogen. You want to know whether this favors the intestinal bacterium Klebsiella, which can fix its own nitrogen. You find 10 volunteers from New Guinea and measure the number of Klebsiella in their intestines, then feed them a protein-rich diet for one month. You then measure the number of Klebsiella in their guts again. Which test should you use?
7. You want to know whether dogs and their owners really look alike. You measure the "mouth droopiness" (vertical distance between the corners of the mouth and the center of the mouth) of 62 dogs and their owners. Which test should you use?
8. You want to know the effect of light source on pumpkins. You grow 10 pumpkin plants under natural sunlight, 10 pumpkin plants under fluorescent light, and 10 pumpkin plants under incandescent light. You remove excess flowers, so each plant will have only one pumpkin. In the fall, you measure the diameter of the pumpkins. Which test should you use?
9. You want to know the effect of temperature on the growth of salmon. You have 10 fish tanks at 10 C and 10 fish tanks at 15 C, and you put 5 newly hatched salmon in each tank. After 6 months, you measure the length of each salmon. Which test should you use?
10. You are planning to do experiments on chicken feed with different ratios of corn meal to soybean meal. To prepare for these experiments, you buy 20 bags of corn meal and 14 bags of soybean meal and put them in a cool, dry place. A few weeks later, when you finally decide to start mixing up chicken feed, you notice that 12 bags of corn meal have moth holes, while 2 bags of soybean meal have moth holes. To find out whether moths prefer corn meal, which test should you use?
11. You are studying the endangered Kaua'i cave amphipod, Spelaeorchestia koloana, which lives in lava tube caves on the island of Kaua'i, Hawaii. You want to know whether the abundance of the amphipods is related to the particle size of the sediments on the bottom of the cave. You put 30 1-m2 quadrats in a cave, count the number of amphipods in each quadrat, and measure the sediment particle size. When you plot a graph of the data, it looks like the intermediate sediment particle sizes have the highest densities of amphipods, with smaller and larger-grained sediment having lower numbers of amphipods. Which test should you use?
12. You want to know whether athletic experience affects the length of people's stride when walking. You measure the length of the walking stride (at 3 miles per hour) of 17 adult men who run 10 or more miles per week for exercise; 14 men who play recreational soccer; and 23 men who do not get exercise involving running. Because it seems likely that men with longer legs would have longer strides, you also measure the length of each man's right leg (hip to floor). Which test should you use?
13. In seahorses, the male carries the developing young in a pouch. You want to know what affects the number of offspring in a brood of seahorses. You capture 57 male seahorses that are carrying young, put them in individual tanks, and count the number of offspring that are released. You measure the weight of the male seahorse, and the length. By examining the annual rings in the otoliths (ear bones), you determine the age of the seahorses. Which test should you use?
14. You have been feeding laying chickens your own custom blend of chicken feed, and you want to know whether it's really better than commercial chicken feed. You have the Single-Comb White Leghorn, Barred Plymouth Rock, and Speckled Sussex breeds of chicken. Each hen is in a separate cage. You feed one hen of each breed your custom chicken feed, one hen of each breed gets MightyChik brand chicken feed, and one hen of each breed gets Purina Chicken Chow. You count the number of eggs each hen lays over a period of 6 months.
15. You are planning to study the effect of salt on blood pressure by surveying the amount of salt in people's diets and measuring their blood pressure. Before you start you study, you're worried that high-salt foods may also tend to be high in fat, and that could make the results of your planned study rather ambiguous. To test this, you buy a variety of foods and measure the salt and fat content of each kind of food. Which test should you use?
16. You want to know whether fruit flies carrying the 8J16 mutation in their Wingless gene differ in the amount of wingless protein. You dissect out a wing imaginal disc from 15 embryos of flies with the mutation, stain for wingless, and measure the amount of stain at 4 random spots in each disc. You do the same for 15 embryos of flies without the mutation. Which test should you use?
17. You want to test three insect species (a caterpillar, a grasshopper, and a weevil) as biological control agents for Japanese honeysuckle, an invasive exotic vine. You design the experiment and decide which statistical test you're going to use. For each species of plant, you set up a cage: one with 50 caterpillars, one with 50 grasshoppers, and one with 50 weevils. After one week, you randomly select 100 leaves from each cage and measure the area of each leaf that has been eaten. What's the next thing you should do?
18. You want to measure the effect of the sex of a chicken on the incubation period of various strains of avian influenza. You inoculate 10 male and 10 female chickens with one strain of avian influenza and measure how many days it takes for each bird to show signs of respiratory distress. You do the same thing for two other strains of avian influenza. Which test should you use?
19. You are studying the effects of bone marrow transplants on the level of T-cells in the blood. You want to know whether recipients of bone marrow tend to have more or fewer T-cells than the person who donated bone marrow to them. You find 17 people who received bone marrow transplants more than 10 years ago, and you also find the bone-marrow donor for each person. You measure the level of T-cells in each person's blood. Which test should you use?
20. You are studying how growth factors affect metastasis (movement) of prostate cancer cells. You treat five cultures of normal cells and five cultures of prostate cancer cells with epidermal growth factor (EGF), and you have five cultures of normal cells and five cultures of prostate cancer cells that you don't treat with EGF. You then do a scratch assay and measure the distance the cells migrate. Which test should you use?
21. You want to know whether plant extracts used in traditional Chinese medicine are effective against prostate cancer. You come back from China with 75 different plant extracts, and you give each one to 5 mice with prostate cancer. After a month, you measure the size of the tumors and do the appropriate statistical test for each extract. The test for celastrol, a substance extracted from roots of the "Thunder of God Vine" (Tripterygium wilfordii), has a P-value of 0.021. How excited should you be about celastrol? Why?
22. Fiddler crabs have pigment cells called melanopores; you want to know whether they use them for camoflauge. You put 20 individually tagged fiddler crabs on a black background for 24 hours, then measure the amount of light reflected off each crab's carapace. You then put the crabs on a white background for 24 hours and measure the amount of light reflected off each crab's carapace. Which test should you use?
23. You want to know whether certain "home remedies" used for ant control really work. You find 40 houses that are infested with pavement ants (Tetramorium caespitum). In 10 of the houses, you place bay leaves along the baseboards; you sprinkle boric acid along the baseboards of 10 houses, sprinkle diatomaceous earth along the baseboards of 10 others, and leave the last 10 houses untreated. After two weeks, you place sticky traps in each house and count the number of ants caught in a 12-hour period. Which test should you use?
24. In order to increase rotation speed during a figure skating jump, skaters must be strong enough to pull their arms in towards the center quickly after taking off. Strength tests have shown that skaters may not have the upper body strength necessary to overcome the centrifugal forces and pull their arms in, so you decide to put female figure skaters through a strength training program. Using a high-speed camera, you measure the rotation speed during the first spin of a triple Lutz-double toe loop combination of 9 top skaters, put them through a 12-week strength training program, then measure the rotation speed again. Which test should you use?
25. You want to test the effect of selenium on growth rate of growing pigs. You have 200 young pigs, all of the same weight. You divide the pigs into 8 groups of 25, and you give each group of pigs a different amount of selenium in its diet. At the end of 6 months you weigh the pigs. Which test should you use?
26. You want to know whether salt marsh restoration affects the proportion of black ducks in an area. You go to 10 degraded salt marshes and count the number of black ducks and the number of ducks in other species at each marsh. The marshes are restored, and three years later, you count the number of black ducks and number of other ducks at each marsh again. Which test should you use?
27. You want to test the effects of anabolic steroids on the muscle strength of elderly people. You put 200 old people on steroids, 200 old people on placebo, and 200 old people on no treatment. After one month, you measure the arm strength of each person. Which test should you use?
28. You've been hired by a turkey company, which wants to know, "Do male turkeys have the same fat content as female turkeys of the same size, or are they different?" You get 20 male and 20 female turkeys of a variety of sizes, weigh them, and measure the fat content of each. You analyze the data using ancova (since fat content might also be associated with weight). The P-value for the difference in slopes is 0.031, while the P-value for the difference in intercepts is 0.007. What answer do you give to the turkey company?
29. You want to know the effect of temperature on the growth of snails. You have 10 fish tanks at 10 C and 10 fish tanks at 30 C, and you put 5 snail eggs in each tank. After 6 months, you measure the length of each snail. What test should you use?
30. You want to know how salinity and temperature affect the taste of oysters. You collect oysters from 15 locations on the East Coast, ranging from Maine to Florida, and record the average annual temperature and average annual salinity at each location. Then you feed one raw oyster from each location to a professional oyster-taster, who rates the taste on a scale from 1 (disgusting) to 20 (delicious). Which test should you use?