Download Tutorial #3: Normal Distributions and Correlations

Tutorial #3: Normal Distributions and Correlations
Warm up questions!
1. I have a distribution that is symmetric and the median is the same value as the mean. This is therefore
a normal distribution.
a) True
b) False
How do you know?
_____________________________________________________________________________________
2. Which of the following is FALSE about a normal distribution?
a) the values in the centre of the distribution are most common
b) the values in the centre of the distribution have the highest scores
c) a Z distribution is a special kind of normal distribution with a mean of 0 and a standard deviation of 1
d) There are common and naturally occurring regarding many psychological phenomena
3. Becky and Mohammed both took the same IQ test. Their scores were then turned into z scores to see
how they compared with their peers. Becky had a z score of -1.2 and Mohammed had a z score of 1.2.
Which of the following is FALSE about their scores?
a) they are both the same number of standard deviations from the mean
b) Becky did worse on the IQ test than Mohammed
c) both are exceptional cases and less than 5% of the population has scores more extreme than theirs
d) all of the above
4. Aaron is applying for grad school and he had to take a standardized entrance exam. The mean score
was 60 and the standard deviation was 10. Aaron got 73.
a) What is his z score? _____________
b) What percentile does that make him? _______________
c) If the school only accepts the top 15 percent, will he get in? _____________
5. An IQ score has a mean of 100 and a standard deviation of 15. What percentage of people fall within 1
standard deviation of the mean?
a) 16%
b) 50%
c) 68%
d) 84%
Sidra has a z-score of 2 for her class test. She is thrilled. If the class mean = 70 and there was a standard
deviation of 8, what is her score?
Li is working on his master’s thesis about the correlation between taking large doses of vitamin D and
depression. He finds r = -.46. Should Li be happy and try to get his work published, or did he fail to find
an effect and must rethink his experiment?
Janice wanted to find out if exercising leads to less pain in those who are chronically ill. She found that
there was a significant correlation between exercising and pain of r = -.20. How might she explain her
findings?
a) exercising relieves pain
b) exercising requires you to have low levels of pain, so only those with lower pain could exercise
c) those with more pain were more likely to be hospitalized or bed-ridden, stopping them from being
able to get to the gym.
d) all of the above
Amy found that there was a correlation of r = .80 between classes attended and final grade in the class.
How much of the variability in final grades can be explained by classes attended?
a) 6.4%
b) 16%
c) 64%
d) 80%
Given the previous example, what would the correlation be if Amy were to study missed classes and
final grade in the class?
a) r = -.80
b) r = .80
c) r = .64
d) not enough information given
Name 3 reasons why you would want to graph a scatterplot before you run a correlation analysis?
a)
b)
c)
Which of the following variables should you NOT use Pearson’s r?
a) height and weight
b) mortality and marital status
c) post-treatment scores on the Beck Depression Inventory and age
d) scores of the Beck Depression Inventory and the Hospital Anxiety and Depression Scale
What happens when you have two sets of data (for example, men and women)and combine them into
the same scatterplot?
a) it increases the correlation because there are more people
b) it decreases the correlation because there is more noise
c) it will not change the correlation because it is not dependent on sample size
d) it can either increase or decrease the correlation