### Final exam study guide: Practice exam 2

Here are some more practice questions for the final exam. To see the correct answer to a question, click on the "Answer" button. Don't bother typing your answer into the box, it won't do anything.

Where two correct answers are shown for these practice questions (such as chi-squared or G-test of independence), you must only write down one on the actual exam.

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. You want to estimate how far pollen from genetically engineered corn will travel. You genetically engineer corn to express green fluorescent protein in its kernels, and you plant a large field of this corn in the spring. That fall, you collect one ear of corn from each of 20 fields at different distances away from the fluorescent corn field. You examine each ear in the dark and count the number of kernels that are fluorescent and the number that are not fluorescent. Which test should you use?
7. 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?
8. 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?
9. 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?
10. 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?
11. 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?
12. 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?
13. You want to determine what affects a person's chances of surviving a heart attack. For 1667 people who have had a heart attack, you record their age, height, weight, and how much time elapsed between the heart attack and reachng a hospital. You also record whether or not they survived the heart attack. Which test should you use?
14. You want to know whether men who wear tight underwear have a higher proportion of female offspring than men who wear loose underwear. You search the literature and find 8 studies on this question, all of which seem like high quality, well designed studies. You combine the results of all of these studies, and men with tight underwear father 1.2 percent more female children than men with loose underwear. This combined result from all the studies has a P-value of 0.037. What is one reason why you might hesitate to reject the null hypothesis that underwear has no effect on sex ratio?
15. 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?
16. You want to know whether keeping sheep in indoor cages affects the weight of their offspring. You weigh 30 newborn lambs from ewes kept full-time in cages, 30 lambs from ewes caged at nights only, and 30 lambs from ewes kept outdoors. Which test should you use?
17. 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?
18. 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.
19. You are a forensic entomologist, and you wonder whether people who were on antibiotics will be colonized by different species of insects after they die than people not on antibiotics. You get 11 pigs and put them on 11 different doses of tetracycline for a week, ranging from 0 to 100 mg/day. You kill the pigs and put them out in the woods for a week, then sample calliphorid fly maggots from each corpse and count the number in two species: Phaenicia regina and P. cuprina. The data range from 34% P. cuprina in the pig given 0 mg tetracycline to 60% P. cuprina in the pig given 100 mg tetracycline/day. Which test should you use?
20. 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?
21. 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?
22. 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?
23. You want to measure the effect of the sex of a chicken on the incubation period of various strains of avian influenza. You inoculate male and female chickens with one of three different strains of avian influenza and measure how many days it takes for each bird to show signs of respiratory distress. Which test should you use?
24. 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. You notice that the differences between donor and recipient are not normally distributed. Which test should you use?
25. 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?
26. 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?
27. 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?
28. 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?
29. 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?
30. 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?
31. You want to know whether areas with lots of goldenrod plants are more likely to have a preying mantis. For each of 250 randomly placed 1-m2 plots in a field, you count the number of goldenrod plants. You also determine whether each plot has a praying mantis in it. None of the plots has more than one praying mantis. Which test should you use?
32. You are a walnut farmer, and you'd like to know whether fertilizing the soil around a tree affects the yield. You fertilize the soil around 50 walnut trees (randomly chosen throughout the orchard) and use 50 trees as the unfertilized control. For each tree, you count the number of walnuts it produces; because bigger trees will produce more walnuts, you also measure the diameter of each tree. Which test should you use?
33. You've heard the saying "an apple a day keeps the doctor away," and you want to see if there really is an association between apple consumption and doctor visits. You find 250 volunteers who record how many apples they eat and how many times they go to the doctor for a year. Which test should you use?
34. You want to know whether the gene that codes for mannose-6-phosphate isomerase (MPI) is expressed differently in liver tumors than in normal livers. You take biopsies from 27 normal livers and 32 cancerous livers and measure the amount of MPI mRNA in each one. Which test should you use?
35. You want to know whether proximity of spicebush (Lindera benzoin) to black walnut (Juglans nigra) reduces the amount of herbivory on spicebush. Early in the spring, you plant 20 spicebush plants at various distances from a black walnut tree; at the end of the summer, count the number of leaves with herbivore damage and the number undamaged by herbivores on each plant. Which test should you use?
36. You are trying to model arm motions in a large number of people, and one of the important parameters is the flexion/extension moment arm of the bicep brachii muscle. It takes a lot of work to measure this accurately, but you think it might be possible to just measure the length of the ulna bone and estimate the flexion/extension moment arm from that. You take a small number of people and measure the length of the ulna bone and the size of the flexion/extension moment arm. Which test should you use?
37. You are trying to figure out what affects litter size in squirrels. You weigh 89 female squirrels at the start of the mating season; once they give birth, you count the number of offspring each female has. You notice that a lot of the squirrels have zero offspring, making offspring number very non-normal, and no transformation will fix this. Which test should you use?
38. You want to know whether mice can see colors. Twenty times a day for two weeks, you put a piece of mouse food in a small red box and put it in a cage with one mouse. The mouse can tip the box over and get the food out. At the same time, you also put mouse food in a green box; it looks and smells the same as the red box, but is glued shut so the mouse can't get the food out. At the end of the two weeks, you put the two boxes in with the mouse for 10 more times. The mouse pushes over the red box first eight times and the green box two times. Which test should you use?