Second exam study guide

This is the study guide for the second exam in Biological Statistics, fall 2007. The exam will be on Tuesday, October 30. You may not use your notes or textbook during the exam; if English is your second language, you may use a dictionary. You will not need a calculator.

The exam is cumulative; about a third of the questions will be about material covered in the first part of the semester. You should look at the first midterm and make sure you understand everything on it, and you should study the topics listed on the study guide for the first midterm.

You should primarily study your lecture notes, the web pages on different topics (linked from the syllabus), and the homework assignments. I have revised some of the web pages, so if you have printed them out, please look at them again. In addition to the topics covered on the first midterm, you should be familiar with:

The exam will consist of about 15 to 20 short-answer questions. Most of them will consist of me describing an experiment, then asking what statistical test is appropriate. On this exam, I will not ask you to lisk the variables in an experiment and say whether they are measurement, attribute or ranked. That is a good way to help you decide on the appropriate statistical test, however. Here are some example questions:

  1. You have placed ten egg masses, each representing a separate family, of treehoppers on a host plant that they don't normally eat. After one month, you measure the body length of each treehopper. You are interested in whether there is genetic variation among the families in ability to grow on this host plant. What are two statistical tests you could use to test whether there is variation among the families in body length?
    How would you decide which was more appropriate?
  2. You are interested in the effects of fertilizer on mitosis in onion root tips. In an onion root tip grown without fertilizer, you count 70 cells in interphase, 28 cells in prophase, 2 cells in metaphase, 5 cells in anaphase, and 10 cells in telophase. In an onion root tip grown with fertilizer, you count 94 cells in interphase, 57 cells in prophase, 9 cells in metaphase, 11 cells in anaphase, and 27 cells in telophase. What statistical test would you use to analyze these data?
  3. You have measured the height of the arch of the foot in athletes from nine women's teams: soccer, basketball, rugby, swimming, softball, volleyball, lacrosse, crew and cross-country. Give a set of at least three orthogonal planned comparisons of the means from these sports.
  4. 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 one biopsy from each of 27 normal livers and 32 cancerous livers and measure the amount of MPI mRNA in each one.
  5. Glacier-Waterton International Park is in Montana and Alberta. While backpacking through the park, you see 8 black bears and no grizzly bears in the Montana side of the park; after crossing the border into Canada, you see no black bears and 6 grizzly bears in the Alberta side of the park. Is there a difference between the two parts of the park in the proportion of bears that are grizzly bears?
  6. You want to know whether 12 clonal strains of E. coli bacteria differ in catabolic activity. You grow three lines of each strain for 2,000 generations, then take three samples of each line and measure the catabolic activity of each sample.
  7. Because of the long tail feathers, male swallows mount the females from either the right or the left. You want to know whether they have a preference for one side, so you observe 17 pairs of mating swallows. Four males mount from the right side, while 13 mount from the left.
  8. 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. Do moths prefer corn meal?
  9. 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 in your notes to find the bone mineral density for the stress-fractured and unfractured legs for these 12 people.
  10. You want to study the effect of exercise on the heart rates of mice. You place 5 male and 5 female mice in a cage with an exercise wheel, and you place 5 male and 5 female mice in a cage without an excercise wheel. After one week, you measure the heart rate of each mouse.
  11. 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, with 120 hens of each breed. Each hen is in a separate cage. You feed half of the hens your custom chicken feed and half of them commercial chicken feed, and you count the number of eggs each hen lays over a period of 6 months.
  12. You are trying to see whether the genes Jam-1 and Pax-6 are genetically linked in zebrafish. You breed two individuals who are heterozygous for visible, dominant mutations at both genes, and you get 1600 offspring. If the two genes are unlinked, you'd expect 100 fish that were normal/normal, 300 that were normal at Jam-1 and mutant at Pax-6, 300 that were mutant at Jam-1 and normal at Pax-6, and 900 that were mutant/mutant.
  13. You want to breed miniature schnauzers that don't bark so much, by selecting those dogs that bark less than others to found the next generation. You obtain 30 miniature schnauzers, raise them under similar conditions, then record how many times each dog barks when a stranger approaches it. You do this five times for each dog.
  14. Two amphipod crustaceans live high on beaches in Delaware, Talorchestia longicornis and Talorchestia megalophthalma. You want to know whether the proportion of each species is different on different beaches, so you collect about a hundred amphipods at Rehoboth Beach, Dewey Beach, Fenwick Island, and Cape Henlopen, and you count the number of individuals of each species at each beach.
  15. You want to know the effect of temperature and light exposure on the growth of eels. You put 25 young eels ("elvers"), all the same size, in each of four tanks: one tank with 10 C water and continuous light, one tank with 30 C water and continuous light, one tank with 10 C water and continous dark, and one tank with 30 C water and continuous dark. After 6 months, you measure the length of each eel.
  16. A zoo has 170 turtles in an outdoor enclosure. There are three rocks in the pen that the turtles like to bask on, one white rock, one brown rock, and one black rock, and you want to know whether the turtles have a preference for one rock over the others. Each rock is the same size, and on a sunny day, all of the turtles are on a rock. You scare the turtles off the rocks, then come back an hour later and count the number of turtles on each rock. You do this each day for a week.
  17. 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. After 3 months, you measure the diameter of the pumpkins.
  18. You want to know whether the presence of the malaria parasite (Plasmodium) in mosquitoes affects the West Nile virus. You collect 1200 mosquitoes. Half of them contain Plasmodium and one-third contain West Nile virus, so your null expectation is that one-sixth (200) of the mosquitoes will have both Plasmodium and West Nile virus. Instead, you find that only 148 mosquitoes have both.
  19. 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 blue box and a green box; they look and smell the same as the red box, but are glued shut so the mouse can't get the food out. Every time you put the three boxes in the mouse cage, you record which box it tries to tip over first. You do this with 10 mice.
  20. You want to test three insect species (a caterpillar, a grasshopper, and a weevil) as biological control agents for four invasive exotic vines (kudzu, porcelainberry, English ivy, and Japanese honeysuckle). For each species of plant, you set up three cages: 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 percentage of the area of each leaf that has been eaten.
  21. You have knocked out the JAM-1 gene in mice, and as part of your investigation of the effects of this gene, you want to know if these genetically engineered mice can tell the difference between low-fat and high-fat food. You have 12 of these mice in individual cages, and you put 20 pellets of low-fat mouse food and 20 pellets of high-fat mouse food in the feeder for each cage. After three days, you count the number of each kind of pellet remaining in each cage.
  22. 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.
  23. 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 their carapace. You then put the crabs on a white background for 24 hours and measure the amount of light reflected off their carapace.
  24. You want to know whether individual starfish, all of the same age, have different mean arm lengths. You collect 27 starfish and measure the length of each of the five arms on each starfish.
  25. A zoo has 17 turtles in an outdoor enclosure. There are three rocks in the pen that the turtles like to bask on, one white rock, one brown rock, and one black rock, and you want to know whether the turtles have a preference for one rock over the others. Each rock is the same size, and on a sunny day, all of the turtles are on a rock. You see 10 turtles on the black rock, 4 turtles on the brown rock, and 3 turtles on the white rock.
  26. 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.
  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 their carapace. You then put the crabs on a white background for 24 hours and measure the amount of light reflected off their carapace. The differences between measurements are not normally distributed.
  28. You want to know the effect of temperature on the growth of eels. You have 10 fish tanks at 10 C and 10 fish tanks at 30 C, and you put 5 elvers in each tank. After 6 months, you measure the length of each eel.
  29. You want to breed miniature schnauzers that don't bark so much, but you don't know whether there is any genetic variation for barkiness. You obtain 7 litters of miniature schnauzers, raise them under similar conditions, then record how many times each dog barks when a stranger approaches it. You do this once for each dog.
  30. 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.
  31. 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.
  32. You have created a mouse model of hypercholesteremia by knocking out the LDLR gene, and you want to know whether they have atherosclerosis ("hardening of the arteries"). You have 12 LDLR-/LDLR- mice, 12 LDLR-/+ mice, and 12 LDLR+/+ mice. You feed the mice a high cholesterol diet for 20 weeks, then prepare 4 cross-sections of the aorta for each mouse. On each cross-section, you measure the area of atherosclerosis lesion.
  33. 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.
  34. When beaches are replenished by dumping new sand on them, the beach animals get covered up and may die. You want to know whether the type of sand makes a difference. You put 20 snails (Ilyanassa obsoleta) at the bottom of each of three large containers, then you put 20 cm of fine sand in one container, 20 cm of medium sand in one container, and 20 cm of coarse sand in one container. After one hour, you count the number of snails that have crawled to the surface in each container.
  35. When a click beetle is on its back, it rapidly flexes its body with an audible "click," flipping itself into the air and hopefully landing right-side-up. You want to know whether this flipping is random or whether the beetles tend to land on their feet. You catch a click beetle, put it on its back, and watch it click. You repeat this 12 times. The beetle lands on its feet 8 times and on its back 4 times.
  36. 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.
  37. 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 blue box and a green box; they look and smell the same as the red box, but are glued shut so the mouse can't get the food out. After the two-week training period, you put the three boxes in with the mouse for 50 times, and you record which box it tries to tip over first. You do this with for five mice.
  38. You have been observing a large troop of monkeys in the Philadelphia zoo. By careful observation of their social interactions, you have figured out the dominance heirarchy: which monkey is dominant over all, which monkey submits only to the most dominant, etc., all the way down to the poor monkey that submits to every other monkey. You want to know whether monkeys born at the Philadelphia zoo tend to dominate monkeys brought from other zoos.
  39. 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 blue box and a green box; they look and smell the same as the red box, but are glued shut so the mouse can't get the food out. At the end of the two weeks, you put the three boxes in with the mouse for 10 more times. The mouse pushes over the red box first seven times, the green box two times, and the blue box one time.
  40. You want to know the effect of light source on pumpkins. You grow 10 pumpkin plants under natural sunlight and 10 pumpkin plants under fluorescent light. You remove excess flowers, so each plant will have only one pumpkin. After 3 months, you measure the diameter of the pumpkins.
  41. You are studying the species diversity of algae in the highlands of Ecuador, and you want to know whether different taxonomic groups of algae are favored in different areas. In a pond at 400 meters elevation, you isolate 5 species of green algae and 3 species of cyanobacteria ("blue-green algae"); in a pond at 1500 meters, you isolate 6 species of green algae and 7 species of cyanobacteria.
  42. 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.
  43. You have knocked out the JAM-1 gene in mice, and as part of your investigation of the effects of this gene, you want to know if these genetically engineered mice have a food preference. You have 20 of these mice in individual cages, and you put a small pile of low-fat mouse food in one corner of each cage and an equal-sized pile of high-fat food in the other corner. After three days, the uneaten food has been mixed in with the litter, so it would be too difficult to weigh it. However, 5 of the cages have piles of uneaten low-fat food that are obviously smaller than the high-fat food piles, 12 cages have piles of high-fat food that are smaller than the low-fat piles, and 3 cages have equal-sized food piles.
  44. It has been hypothesized that bright colors in birds are a signal to potential mates that the brightly colored individual is healthy and therefore would be a good parent. To test the relationship between healthiness and brightness, you buy 20 healthy parakeets and take a picture of each one. You then infect the birds with avian malaria, and after a month of the birds being sick, you take another picture. You show the two pictures for each bird to your collaborator (without saying which is the sick bird) and ask which one looks more brightly colored.
  45. You want to know whether aspirin taken during pregnancy has an effect on the sex of offspring. You ask 1072 new mothers whether they took aspirin during the first three months of their pregnancy, and you also ask them whether they had a boy or a girl.
  46. You want to know whether the JAM-1 gene affects the thickness of mouse corneas, so you genetically engineer mice that are missing JAM-1. You have 5 mice that are missing JAM-1 and five mice with JAM-1. You pluck out both eyes from each mouse and measure the thickness of the cornea at 3 random points.

    47. Return to the Biological Statistics syllabus

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    This page was last revised October 25, 2007. Its URL is http://udel.edu/~mcdonald/statstudy2.html