PS/CJ 3115 Research Methods
Spring 2012
Final Exam Study Guide
The final will have two parts: Part I will include: 1) Matching, 2) conceptual short answer, 3)
SPSS-related short answer. Part II will include: 4) calculation of probability and standard
deviations, and 5) Interpreting statistical output.
Note: The second section of the exam (probability/standard deviation) will require the use of a
calculator, but you won't need one on Wednesday.
Matching.
The matching section will include a selection of words from this list. These all appeared in both
lecture and the textbook.
concept
variable
validity
reliability
unit of analysis
measure of central tendency
measure of association
measure of variation
variable
variation
mean
median
levels of measurement
nominal (level of measurement)
ordinal (level of measurement)
ratio (level of measurement)
dependent variable
independent variable
hypothesis
negative relationship (or correlation)
positive relationship (or correlation)
intervening variable
antecedent variable
spurious correlation
control variable
lab experiment
field experiment
sample bias
questioner bias
inferential statistics
descriptive statistics
normal distribution
population
sample
standard deviation
Z-score
P-value
Chi-squared score
Conceptual Short Answer
The questions in this portion of the exam will resemble the short answer questions that appeared
in the quizzes. They will draw on material presented in class, and principally material that
appeared on the powerpoint slides. I would start studying for this section by making sure you
have the right answers for all the quiz questions. Some of them may appear on the exam
verbatim, others may be paraphrased.
For example, the one lecture included a slide that said:
"Measures of Association tell us how strong the relationship
between two variables is."
So I will likely ask a question such as this:
"A measure of association tells us _________________________________"
or
"What do measures of association tell us: ___________________________"
Another example: I said
"Intervening variables: Come between the independent and the
dependent variables."
So I might ask a question like:
"What do we call variables that come between the independent and dependent variables?"
or
"My theory says that warmer weather causes sunburn, because warmer weather causes people to
expose more skin, which leads to more sunburn. Identify the Dependent, Independent, and
Intervening variables in my theory."
Some specific hints:
I will ask you to define statistical significance.
I will ask short answer questions about the relationship between standard deviation, normal
distribution, t-score, and p-value.
I will describe a survey situation and ask you what kind of bias it describes.
I will ask about the different types of research design. Know what they are and the
advantages/disadvantages of each.
I will ask about the definitions of reliability and validity.
I will give you some variables and ask you to identify what level of measurement they are at.
I will give you several sets of variables, and ask which measure of association you should use with
them (lambda, Somer's D, Pearson's R).
SPSS-related Short Answer
Data Spreadsheets
Alabama
Alaska
Violent Crime Rate
426
634
Homicide Rate
5.5
5.6
Rape
38
85
Be able to:
a. Circle a VARIABLE
b. Draw a box around a VALUE
c. Underline an entire OBSERVATION
You learned the following commands. Make sure you can identify which each one does and
when you would want to use it. I will ask short answer questions like:
"Sex is a nominal variable. What command would I use to learn the distribution of
values for the sex variable in my dataset? ___________________"
Data View / Variable View
Data labels
Recode
Compute new variable
Filter Cases
Frequencies
Descriptives
Independent Sample T-Test
Chi-squared test of independence
I will not ask really detailed questions about the exact command syntax, like "What does the
statistics box in the cross-tab window do?"
Calculation of probability and standard deviations
1) Know how to calculate the mean and median of a set of integers.
2) Know the standard deviation formula and how to calculate it for a data set of integers.
Sample 1: 4,6,2,5,9
ANSWER: median=5, mean=5.2, SD=2.6)
Sample 2: 3, 8, 12, 5, 2, 10, 3
3) Know how to calculate the probability of multiple events happening.
On a six-sided die, what is the probability that I’ll roll a 5?
What is the probability of rolling ‘boxcars’ (i.e. two sixes) when throwing two dice?
If I draw 5 cards in a row from the top of a full deck, what is the probability they will make a flush
(in other words, that they are all the same suit).
If I flip a coin three times, what is the probability that I’ll get 3 heads in a row?
Before the 2008 election, the website fivethirtyeight.com did some great
work on electoral probability. The table here lists estimated
probabilities that Obama or McCain would win Midwestern states.
What was the estimated probability that Obama would win all four
Midwestern states?
What is the probability that McCain would win all four?
4) Know how to use the inverse probability in calculations of multiple events.
Calculate the probability that Obama would lose all four states.
If there is a 20% chance of rain every day, what is the probability it will rain at least once this
week?
If the Harris Teeter stocking crew is doing is job right, there is a 10% of finding a broken egg in
any random carton. If I go shopping for eggs three times, and find a broken egg in my carton
each time, what is the probability that could have happened if they are doing their job properly?
Is that evidence they are not doing it properly?
A new player comes to ultimate frisbee scrimmages in Boone, who says he played for Ring, a
Raleigh club team. If he really was good enough to play for Ring, he should get through games
without a single dropped disc 75% of the time. The first two games he plays in, he drops it both
times. What is the probability of that happening if he really did play for Ring? Should I be
suspicious?
Interpreting statistical output
Remember, when I say "interpret your results," you should do 3 things.
1) Tell me the answer. For example: (for a T-test) "On average, Men study 2.5 more hours per
week than women do," or (for correlation) "People with longer index fingers tend to have longer
ear lobes."
2) Tell me whether the connection is statistically significant. For example: "This result is
statistically significant," or "I am not confident these sample results apply to the whole
population."
3) Give me the evidence. For example: (Pearson's R = .325), (P<.001), or Lamda=.43, P=.012).
DO NOT GET LITERARY ON ME. I've seen more of these answers than you care to imagine,
and I can assure that not matter how sophisticated you think you are, if you try to creatively mix
your parts 1 and 2, you will probably make a mistake and lose points.
KEEP IT SIMPLE. If your results show that "poor neighborhoods have more crime than rich
neighborhoods," then say that! Don't give me something like "There is a correlation between the
level of poverty and the crime rate at the neighborhood level." Answers your grandmother can
understand are better than ones she can't.
T-tests
In his survey this semester, Justin discovered that most (70%) of ASU students were willing to
drive after drinking. I suppose that matches the reports from people who observed court
proceedings for this class and said it was mostly DUIs. Anyway, when I first read his
explanation, I wondered about three possible hypotheses: a) Older people are wiser and less likely
to drive after drinking, b) Younger people aren't legally drinking, so they're more cautious and less
likely to drive after drinking, or c) age doesn't matter. Here's the result of a T-Test I did.
Interpret the results and decide if there is evidence for any of the three hypotheses. Make sure
you assess whether the results of Justin's sample can be extrapolated to the whole ASU
population. [the dependent variable is "would you drive after drinking, where 1=never, 2=as a
last resort, and 3=yes] (4 points)
SPSS says: Under-21 average: 1.62, Over-21 average: 1.45 t-score=.547 p-value= .588
Next I wondered if males or females are more likely to drink and drive. After some thought, I
decided that males might have been more likely to 50 years ago, but I don't get the sense that
current female students show much more self-restraint around alcohol than male students do.
Here is the result of a T-Test. Use these results to make a case that: a) Men DUI more, b)
Women DUI more, or c) the data doesn't provide good evidence either way. Make sure you use
the statistical results to support your position. (4 points)
SPSS says: Male average: 1.64, Female average: 1.33 t-score=1.740 p-value= 0.11
Pearson's R
In class I showed you my collection of data from student course evaluations, and we checked
hypotheses about what factors made students think a teacher was effective. Remember all
variables in this data set are rated from 1 (strongly disagree) to 5 (strongly agree) One possibility is
that students respond positively to an enthusiastic professor. When I correlated "Effective
Teacher" with "Enthusiastic" I found a Pearson's R of 0.6509, with a p-value of .002. (4 points)
Is the correlation positive or negative?
How strong is the correlation?
Is it statistically significant?
Explain what this correlation (or lack thereof) says about teaching styles to your grandma.
Among teachers, there is a perennial debate about whether students give better evaluations for
professors who go easy on them or whether ease doesn't matter. To test this, I did a correlation
between "Teacher is Effective" and "Course is Difficult." I found a Pearson's R of .1043, with a pvalue of .11. (4 points)
Dr. Koch says that students respond positively to difficult classes. If he is right, would
Pearson's R be positive or negative?
How strong is the correlation?
Is it statistically significant?
Explain this correlation (or lack thereof) to your grandma.
One of the CJ profs who left the department in the past few years had good evaluations, but also
gave "A"s to pretty much everyone in the whole class. Some people said that the evaluations
didn't mean anything since they were "bought" with good grades. Based on the evidence above,
do you agree? Why?
Measures of Association and Chi-squared
One student this summer did an interesting survey that asked students if they "enjoyed college."
Fewer than half said yes. There's a lot one might speculate about from that result, but most of it is
beyond the scope of this exam, unfortunately.
On average, girls do better in college than boys do, so I hypothesized they enjoy college more,
since we usually like doing what we excel at. This is what SPSS tells me.
Am I right? Interpret the results, making sure to
include a description of the correlation (with the
relevant number), the statistical significance (with
the relevant number)--but don't forget to answer
the question. (4 points)
The student also asked whether the respondents drink alcohol. Given all the drinking that
students do, I hypothesized that young people who drink will enjoy college. Here is the SPSS
output.
Am I right? Interpret the results, making
sure to include a description of the
correlation (with the relevant number), the
statistical significance (with the relevant
number)--but don't forget to answer the
question. (4 points)