11/9/11 9:03 PM Grade Test: Midterm Page 1 of 7 https://courses.northwestern.edu/webapps/assessment/do/gradeTest…%3Fcourse_id%3D_291438_1%26cmd%3Dnext%26sequenceId%3D_291438_1_1 2011Fall MED_INF_409-DL_SEC55 Introduction to Biostatistics 2011FA_MED_INF_409- DL_SEC55 Grade Center Grade Test: Midterm Edit Mode is: ON Grade Test: Midterm Assign a grade and feedback for the current test attempt. When available, click Save and Next or View Previous to navigate through or grade the attempts in the queue one at a time. If no grade is assigned to the attempt, clicking Save and Next will not change the status of the attempt. If multiple attempts for a test have been allowed, a Student's grade is not released until all of the attempts have beeen graded. Click Hide User Names to grade attempts anonymously. Click Show User Names to display user information. More Help Exit Save and Exit View Previous Save and Next View: Full Grade Center 23 Total User: David Schlossman (Attempt 1 of 1) Status: Completed Item: 6 of 23 Test Information A __________ is a quantity computed from the scores in a population; a ______ is a quantity computed from the scores in a sample. (2 pts) Given Answer: a. parameter; statistic Correct Answer: a. parameter; statistic Question 1: Multiple Choice 2 out of 2 points Which of the following is an example of ordinal scale data? (2 pts) Given Answer: b. Health rating of excellent, very good, good or fair Correct Answer: b. Health rating of excellent, very good, good or fair Question 2: Multiple Choice 2 out of 2 points You are designing an operations manual for a research project which includes the statistical plan. The statistician indicated the study should include randomization without replacement. What steps would you include and why? (2 pts) Given Answer: There are three classic methods for selecting a simple random sample without replacement: 1. Lottery Method : The members of the population are assigned numbers from 1 to N, and the numbers are written on slips of paper, round balls, or some other medium of identical size and shape. The slips or balls are placed in a container and mixed thoroughly. Then a slip or ball is picked out, the slips/balls are mixed again, another slip is picked, and so on. The procedure repeats until the desired number of slips (sample size=n) has been picked. Since the slips are not replaced between rounds of choosing, the sampling is "without replacement." The method works well for small Question 3: Short Answer 2 out of 2 points Hide User Names Jump to...
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11/9/11 9:03 PMGrade Test: Midterm
Page 1 of 7https://courses.northwestern.edu/webapps/assessment/do/gradeTest…%3Fcourse_id%3D_291438_1%26cmd%3Dnext%26sequenceId%3D_291438_1_1
2011Fall MED_INF_409-DL_SEC55 Introduction to Biostatistics 2011FA_MED_INF_409-DL_SEC55Grade Center Grade Test: Midterm
Edit Mode is: ON
Grade Test: Midterm
Assign a grade and feedback for the current test attempt. When available, click Save and Next or View Previous to navigatethrough or grade the attempts in the queue one at a time. If no grade is assigned to the attempt, clicking Save and Next willnot change the status of the attempt. If multiple attempts for a test have been allowed, a Student's grade is not releaseduntil all of the attempts have beeen graded. Click Hide User Names to grade attempts anonymously. Click Show UserNames to display user information. More Help
Exit Save and Exit View Previous Save and Next
View: Full Grade Center 23 TotalUser: David Schlossman (Attempt 1 of 1) Status: Completed Item: 6 of 23
Test Information
A __________ is a quantity computed from the scores in a population; a ______ is a quantity computed from thescores in a sample. (2 pts)
Given Answer: a. parameter; statistic
Correct Answer: a. parameter; statistic
Question 1: Multiple Choice 2 out of 2 points
Which of the following is an example of ordinal scale data? (2 pts)
Given Answer: b. Health rating of excellent, very good, good or fair
Correct Answer: b. Health rating of excellent, very good, good or fair
Question 2: Multiple Choice 2 out of 2 points
You are designing an operations manual for a research project which includes the statistical plan. Thestatistician indicated the study should include randomization without replacement. What steps would youinclude and why? (2 pts)GivenAnswer:
There are three classic methods for selecting a simple random sample without replacement:1. Lottery Method: The members of the population are assigned numbers from 1 to N, and thenumbers are written on slips of paper, round balls, or some other medium of identical size andshape. The slips or balls are placed in a container and mixed thoroughly. Then a slip or ball is pickedout, the slips/balls are mixed again, another slip is picked, and so on. The procedure repeats untilthe desired number of slips (sample size=n) has been picked. Since the slips are not replacedbetween rounds of choosing, the sampling is "without replacement." The method works well for small
Question 3: Short Answer 2 out of 2 points
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Midterm Part 1
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populations, but is cumbersome for large populations.2. Using a Random Number table: Again, the members of the population are assigned numbers from1 to N (or from 0 to N-1). The researcher then consults a random number table (many available bothin print or on line) to choose the random sample. For example, suppose we want to select a randomsample of 10 from a population of 100. We number the population units from 00 to 99 and select tentwo-digit numbers from a random number table. If any number occurs twice, we ignore the secondoccurrence because the sampling is without replacement.Computer Algorithm: There are a large number of standardized computer methods in print and online for selecting a simple random sample without replacement. Most of them depend on selectingrandom (actualy pseudorandom) numbers using one of many available algorithms. Many that I havefound on line reference Donald Knuth's classic The Art of Computer Programming volume 2(Seminumerical Algorithms). One example written in Python would be:## {{{ http://code.activestate.com/recipes/272884/ (r1)def sample(n, r): "Generate r randomly chosen, sorted integers from [0,n)" rand = random.random pop = n for samp in xrange(r, 0, -1): cumprob = 1.0 x = rand() while x < cumprob: cumprob -= cumprob * samp / pop pop -= 1 yield n-pop-1
# Example call to select three samples in range(0,10)>>> list(sample(10, 3))[2, 7, 8]## end of http://code.activestate.com/recipes/272884/ }}}Retrieved from http://code.activestate.com/recipes/272884-random-samples-without-replacement/
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For a normal distribution with a mean of 80 and a standard deviation of 10, find the probability value for p(X <95). (1 pts)Given Answer: Z= X-mu/sigma=95-80/10=1.5. P(X < 95)=P(Z < Z1.5)=0.9332.
Question 4: Short Answer 1 out of 1 points
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For a normal distribution with a mean of 80 and a standard deviation of 10, find the probability value for p(85 <X < 95). (1 pts)Given Answer: Z=X-mu/sigma=85-80/10=0.5. P(X < 85)= P(Z < Z0.5)=0.6915.
For a normal distribution with a mean of 140 and a standard deviation of 55 find each value requested. (2 pts)a. What is the score needed to be in the bottom 10% of the distribution?b. What scores form the boundaries for the middle 75% of the distribution.
GivenAnswer:
a. X=mu+(Z x sigma) so X=140+ (Z0.1 x 55). Z0.1 = -1.285. Therefore X=140+(-1.285 x 55)=140-
Question 6: Short Answer 2 out of 2 points
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70.675=69.325. Any score less than 69.325 will be in the bottom 10% of the distribution.b. Scores in the middle 75 % of the distribution will be between Z0.125 and Z0.875.Z0.125 = -1.15 and Z0.875 = 1.15. X=mu+(Z x sigma).X=140+(-1.15 x 55)=140-63.25=76.75 and X=140+(1.15 x 55)=140+63.25=203.25.Therefore the middle 75% of the distribution lies between 76.75 and 203.25.
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We are testing the effects of a new flu medicine in a randomly drawn sample of 10 year old children with the fluand compare the length of their illness to the mean length of illness in the population of untreated 10 year oldchildren with the flu. The t statistic for our sample falls within the critical region. We should ________. (2 pts)
Given Answer: d. Both a and b
Correct Answer: a. Reject the Null hypothesis
Question 7: Multiple Choice 0 out of 2 points
We are testing the effects of a new therapy for depression in a randomly drawn sample of depressed patientsand compare their depression scores at the end of therapy to the mean depression score in the population ofuntreated depressed patients. Our single sample t statistic does not fall within the critical region. We should____________.(2 pts)
Given Answer: b. Fail to reject the H0
Correct Answer: b. Fail to reject the H0
Question 8: Multiple Choice 2 out of 2 points
When we know the value of the population standard deviation, we use which of the following tests? (2 pts)
Given Answer: b. z test
Correct Answer: b. z test
Question 9: Multiple Choice 2 out of 2 points
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Class discussion later showed that answer d was correct.
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In general, the interval width of a confidence interval _______ as sample size (n) gets larger and ________ as theconfidence level increases. (2 pts)
Given Answer: gets smaller, gets larger
Correct Answer: gets smaller, gets larger
Question 10: Multiple Choice 2 out of 2 points
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You are designing a study to determine whether music has an effect on learning. Previous research indicates thatthe standard deviation to learn a task is 3.4 minutes. How many subjects would you need to ensure with 90%confidence that the estimate is within 1 minute of the true mean time required? (2 pts)Given Answer: n=((Z1-alpha/2 x sigma)/E)2 = ((Z0.95 x 3.4)/1)2 = ((1.645 x 3.4)/1)2 = (5.593)2 = 31.28 so
we need 32 subjects.CorrectAnswer:
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A Gallup Poll shows that 60% of voters support the new health care reform bill. If nine voters are randomly selected,what is the probability that at least three voters favor the new health care reform bill? (2 pts)GivenAnswer:
The result is calculated using the binomial distribution with n=9 and p=0.6. The probability that at least 3voters favor the bill is:P(3)+P(4)+P(5)+P(6)+P(7)+P(8)+P(9)=0.0743+0.1672+0.2508+0.2508+0.1612+0.0605+0.0101=0.9749
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Use the attached Excel dataset titled “CardioStudy.xls” for this problem. This dataset contains data from a
cardiovascular study, which looked at the relationship between cardiovascular disease and a set of risk factors. The
data set contains one record per subject and has the following variables:
Variable Description Data Type Range of Values
ID 5-Digit Unique Subject
Identifier
Numeric 101-96017
CVD Cardiovascular Disease Numeric No = 0
Yes = 1
TRT Treatment Group Numeric 0 = Placebo
1 = Drug
AGE Subject’s Age Numeric 34-60
HDL HDL Cholesterol Numeric 18-98
LDL LDL Cholesterol Numeric 155-428
SMOKER Smoking Status Numeric 0= No
1 = Yes
1. Using the dataset CardioStudy Run the appropriate analysis to answer each of the following questions.
Paste the appropriate tables or graphs into your response as appropriate.
a. What percent of the subjects are in the PLACEBO treatment group? (1 pt)
TREATMENT FREQUENCIES
Frequency Percent Valid Percent
Cumulative
Percent
Valid 0=Placebo 10 50.0 50.0 50.0
1=Drug 10 50.0 50.0 100.0
Total 20 100.0 100.0
Fifty percent of the subjects are in the Placebo treatment group.