Biological Data Analysis:
Second exam study guide
This is the study guide for the second exam in Biological Data Analysis,
spring 2018. The exam will be on Thursday, April 12. 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.
is cumulative; several of the questions will be about material
covered in the first part of the semester. You should look at the first
exam and the first study guide again.
You should primarily study
your lecture notes, the web pages on different topics (linked from the
syllabus), and the homework assignments. In
addition to the topics covered on the first exam, you should be
- Mean and median
- Standard deviation, standard error, and confidence intervals
- One-sample t-test
- Student's two-sample t-test
- Welch's two-sample t-test
- Fisher's one-way anova
- Welch's one-way anova
- Partitioning of variance
- Tukey-Kramer method
- Assumptions of anova
- Data transformations
- Kruskal-Wallis test
For Welch's two-sample t-test vs. Student's two-sample t-test, you must answer Welch's if the question implies that the data are heteroscedastic and unbalanced. (A question probably won't say "The data are heteroscedastic," it would say something like "You notice that the standard deviations of the groups are very different" or "the individual observations are much more spread out in one group than in the other.") If the question does not say that the data are heteroscedastic and unbalanced, you may say either Welch's or Student's two-sample t-test. You must be aware when both are appropriate and when only Welch's is appropriate. Likewise, you must answer Welch's anova if an anova experiment is heteroscedastic and unbalanced, you may say either Welch's or Fisher's one-way anova when the question does not imply that the data are heteroscedastic or unbalanced.
When there is one nominal variable with two values and one measurement variable, you may say either two-sample t-test (Student's or Welch's, as appropriate) or Fisher's or Welch's one anova. If the nominal variable has more than two values, you must say Fisher's or Welch's one-way anova.
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.
exam, I will not ask you to lisk the variables in an experiment and
say whether they are measurement, nominal or ranked. That is a good way
to help you decide on the appropriate statistical test, however.
some example questions:
- You are interested in the effects of fertilizer on
mitosis in onion root tips. In an onion root tip grown without fertilizer,
you count 701 cells in interphase, 283 cells in prophase, 29 cells in
metaphase, 56 cells in anaphase, and 100 cells in telophase. In an onion
root tip grown with fertilizer, you count 942 cells in interphase, 576 cells
in prophase, 97 cells in metaphase, 115 cells in anaphase, and 273 cells in
telophase. What statistical test would you use to analyze these data?
- You want to know whether the gene that codes for mannose-6-phosphate
isomerase (MPI) is expressed differently in livers with liver cancer, livers with cirrhosis, and normal
livers. You take one biopsy from each of 17 cancerous livers, 12 cirrhotic livers, and 32 normal livers
and measure the amount of MPI mRNA in each one. According to what you've learned so far in this class, what are all the tests that you might be able to use to test the hypothesis that the three means are equal? What would tell you that you shouldn't use one or more of these tests?
- 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. You want to know whether moths prefer corn
meal; which test should you use?
You want to test the effects of anabolic steroids on the muscle strength of elderly people. You put 150 old people on steroids, 200 old people on placebo, and 350 old people on no treatment. After one month, you measure the arm strength of each person. The standard deviation of arm strength for people on steroids is much higher than for the other two groups. Which test should you use?
- 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
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. Which test should you use?
- Two amphipod crustaceans live high on sandy 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 go to Rehoboth
Beach, Dewey Beach, Fenwick Island, and Cape Henlopen, collect about 500 amphipods from each beach, and count the
number of individuals of each species at each beach. Which test should you use?
- 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. When the pumpkins are three months old, you
measure the diameter of the pumpkins. Which test should you use?
- 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. What should you do next?
- You want to breed miniature schnauzers that don't bark so much, but
you don't know whether there is any genetic variation among families 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. Which test should you use?
- 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?
- You have been observing a large troop of monkeys in the Philadelphia
zoo. Some of the monkeys were born there, and the other monkeys were brought there from other zoos. By careful observation of their social interactions, you have put the monkeys in order from most dominant to least dominant: 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 be more dominant compared with monkeys brought from
other zoos. Which test should you use?
- 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. Which test should you use?
Return to the
Biological Statistics syllabus