Epidemiology

Mod 2 Assignment 2

Question 1:

An epidemiological investigation was begun on July 1, 2000 among a population of 1,000 individuals. Three individuals were found to have leukemia on July 1st. During the ten-year follow-up period, five new cases of leukemia were diagnosed. Among the eight leukemia cases, four deaths occurred during the ten-year follow-up period. Two additional individuals, neither of whom had leukemia, were lost to follow-up at some point during follow-up. None of the remaining 990 study participants became ill, died, or were lost to follow-up during the follow-up period.

The diagram below indicates the experience of the 10 study participants, using the following symbols:

* :case recognition (diagnosis of leukemia)
*< :onset of leukemia was prior to start of study period
—- :observation period during follow-up
X :status at termination of observation (i.e., alive, dead, lost)

 

case   2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010  
1       — –*– —– —– —– —– —– —– —– —– –X alive
2       — —— —– –*– —– —– —– —– —– —– –X alive
3 *<– —— —— —– —– —– —– —– –X       dead
4       — —— —– —– –X             lost
5       — —— —– —– —– —– –*– –X       dead
6       — —— —– —– —– —– —– —– —– –*– –X alive
7       — –*– —– —– –X             dead
8 *<– —— —— —– —– —– —– —– —– —– —– –X alive
9       — —— —– —– —– —– —– –X       lost
10 *<– —— —— –X                 dead
  • What was the prevalence of leukemia on January 1, 2005?
  • What was the cumulative incidence of leukemia during the 10-year follow-up period?
  • What was the incidence rate of leukemia during the 10-year follow-up period?
  • What was the case fatality rate during the 10-year follow-up period?

 

 

 

 

 

 

Mod 3

Question 1

For this problem, note the following chart:

Age Group
(in years)
% of Population in Age Group Influenza Rate per 1,000 person-years
  CITY A CITY B CITY C Massachusetts CITY A CITY B CITY C
YOUNG 40% 50% 80% 60% 2 10 30
OLD 60% 50% 20% 40% 70 110 5

 

There are 10,000 individuals in City A, which is located in Massachusetts. Eight young individuals and 420 old individuals develop the flu over the course of a year.

  • Use these data to calculate the crude influenza rate per 1,000 individuals per years in City A.
  • What is the crude rate of influenza in City B?
  • What is the crude rate of influenza in City C?
  • Calculate an age-adjusted influenza rate for each of the cities. Use the age distribution for the State of Massachusetts (shown in the table) as the standard.

 

Question 2:

The following table describes hypothetical age-specific rates of heart disease in India and the United States in 2009. Also included are hypothetical age distributions for the two countries and the entire world population.

Age Group
(in years)
% of Population in Age Group Heart Disease Rate per 100,000 person-years
  INDIA U.S.A. WORLD INDIA U.S.A.
< 30 60% 30% 50% 50 75
30-55 30% 40% 30% 80 150
> 55 10% 30% 20% 120 400
  • Calculate the crude rate of heart disease for each of the two countries. Suppose that you want to compare the rate of heart disease in India to that in the United States. You know that age is an important risk factor for heart disease. Examine the age distribution of each country’s population.
  • Should you use the two crude rates to compare the two countries? Why or why not?
  • Calculate an age-adjusted rate for heart disease in each country. Use the age distribution of the entire world as your standard.
  • Based on these answers, would you say that the age differences between India and the United States account for the entire difference in crude heart disease rates between the two countries?  Why or why not?

 

 

 

 

 

 

 

 

MOD 5

Question 1

 

A cohort study was undertaken to examine the association between high lipid level and coronary heart disease (CHD). Participants were classified as having either a high lipid level (exposed) or a low or normal lipid level (unexposed). Because age is associated with both lipid level and risk of heart disease, age was considered a potential confounder or effect modifier and the age of each subject was recorded. The following data describes the study participants: Overall, there were 11,000 young participants and 9,000 old participants. Of the 4,000 young participants with high lipid levels, 20 of them developed CHD. Of the 6,000 old participants with high lipid levels, 200 of them developed CHD. In the unexposed, 18 young and 65 old participants developed CHD.

  • Construct the appropriate two by two tables using the data given above. Be sure to label the cells and margins.
  • Calculate the appropriate crude ratio measure of association combining the data for young and old individuals.
  • Now, perform a stratified analysis and calculate the appropriate stratum-specific ratio measures of association. What are they?
  • Do the data provide evidence of effect measure modification on the ratio scale? Justify your answer

 

Question 2:

 

Name four types of information bias. Name at least one way in which each type of bias can be prevented or minimized.

 

Question 3:

 

A study used self-administered mail questionnaires to gather data on height and weight in order to calculate a measure of obesity. Which of the following types of problems were likely avoided by this method of data collection, and why?

 

  • Interviewer bias
  • Exposure misclassification
  • Confounding
  • Selection bias
  • Loss-to-follow-up

 

 

MOD 6 Questions

QUESTION 1

  1. An epidemiological study involved the comparison of per capita annual income and annual rate of teenage pregnancy in Massachusetts counties in 2012. What type of study is this?
a. Case report
b. Case series
c. Ecological study
d. Cross-sectional study

  

QUESTION 2

  1. A case-control study was conducted to evaluate the relationship between aspirin use and the risk of colon cancer. 2,000 cases and 2,000 controls were enrolled in the study. 1,800 of the cases reported using aspirin in the past while 1,200 of the controls reported using aspirin in the past. What measure of association should be calculated to determine the strength of the relationship between aspirin and colon cancer?
a. Rate ratio
b. Risk ratio
c. Odds ratio
d. Attributable risk

   

QUESTION 3

  1. A cohort study of coffee drinking and anxiety was conducted at a university campus. There were a total of 30,000 freshmen who participated. 10,000 were coffee drinkers and 20,000 were not. Of the coffee drinkers, 500 developed anxiety during the 4 year follow-up period. Of the non-coffee drinkers, 200 developed anxiety during the same time period. Assume that no one in the population died or was lost during the follow-up period. Calculate the population risk difference using the given data. The numeric value of the population risk difference is…
a. 1.3 (per 100)
b. 2.7 (per 100)
c. 3.3 (per 100)
d. None of the above

   

QUESTION 4

  1. A cohort study of coffee drinking and anxiety was conducted at a university campus. There were a total of 30,000 freshmen who participated. 10,000 were coffee drinkers and 20,000 were not. Of the coffee drinkers, 500 developed anxiety during the 4 year follow-up period. Of the non-coffee drinkers, 200 developed anxiety during the same time period. Assume that no one in the population died or was lost during the follow-up period. Which of the following is the correct interpretation of a risk difference calculated from this study?
a. Coffee drinkers are “x” times as likely to develop anxiety as compared to non-coffee drinkers.
b. The excess risk of anxiety among the coffee drinkers is “x” as compared to non-coffee drinkers.
c. The excess risk of anxiety among the entire freshmen population is “x”
d. None of the above

 

QUESTION 5

  1. In January, 2001 forty heterosexual hemophiliac patients (all males) were asked to participate in a 3 year prospective study . The men were to undergo an interview, physical examination, and blood testing for HIV status every 6 months for 3 years. Among the 40 subjects there were 30 who were seronegative and healthy for the entire duration of the study, and all of these were followed for the entire 3 years. During the initial screening, 2 of the men were found to already be HIV+, although none of them had clinical signs of AIDS. The table below describes the 10 subjects who either tested HIV positive, or became lost to follow-up, or already were HIV positive at the start of the study.

Legend:

HIV+   = found to be HIV+ at the very beginning of the interval observation period

?          = lost to follow-up

      ************* Follow-up **********************
Subject # Initial Screening   Jan. 2001 June 2001 Jan. 2002 June 2002 Jan. 2003 June 2003
1     ——— ——— ——— ——— ——— HIV+–
2     ——— ——— ——— ——— ——— ?
3     ——— ——— HIV+– ——— ——— ———
4     ——— ?        
5     ——— ——— ——— ?    
6     ——— ——— ——— ——— ——— ?
7     ——— HIV+– ——— ——— ——— ———
8     ——— ——— ——— ——— ——— ?
9 HIV+   ——— ——— ——— ——— ——— ———
10 HIV+   ——— ——— ——— ——— ——— ?

 

What was the cumulative incidence of seropositivity (HIV+) during the 3 year study?

a. 5/40
b. 3/10
c. 5/35
d. 3/38

 

QUESTION 6

  1. A cohort study of coffee drinking and anxiety was conducted at a university campus. There were a total of 30,000 freshmen who participated. 10,000 were coffee drinkers and 20,000 were not. Of the coffee drinkers, 500 developed anxiety during the 4 year follow-up period. Of the non-coffee drinkers, 200 developed anxiety during the same time period. Assume that no one in the population died or was lost during the follow-up period. What was the cumulative incidence of anxiety among coffee drinkers?
a. 2.0 % over a four year period.
b. 5.0 % over a four year period.
c. 1.0 % over a four year period.
d. None of the above

 

QUESTION 7

  1. Suppose that your company has just developed a new screening test for a disease and you are in charge of testing its validity and feasibility. You decide to evaluate the test on 1000 individuals and compare the results of the new test to the gold standard. You know the prevalence of disease in your population is 30%. The screening test gave a positive result for 292 individuals. 285 of these individuals actually had the disease on the basis of the gold standard determination. Calculate the predictive value of a positive test:
a. 93.7%
b. 97.6%
c. 99%
d. 95%

 

QUESTION 8

  1. Consider the situation in a case-control study where the crude odds ratio is 4.6. The data are then divided into two groups. In the first group the group-specific  odds ratio is 1.0, and  the second group’s odds ratio is 3.0. Which of the following is present?
a. Positive confounding
b. Negative confounding
c. Positive confounding and effect modification
d. Negative confounding and effect modification

 

QUESTION 9

  1. Three principles guide research that involves human participants. These are:
a. Respect for persons, beneficence, and justice
b. Confidentiality, compensation, and avoiding harm
c. Equitable access to benefits of research, moral rightness in action or attitude, minimizing risk

 

QUESTION 10

  1. A cross-sectional study was conducted on the association between passive smoke inhalation and the occurrence of dental caries in children. (Passive smoke exposure occurs when children live with family members who smoke.) The investigators thought that conclusions from this study were limited because of the cross-sectional nature of the data. Suppose that they asked you for advice and you told them that they should have conducted a prospective cohort study because it is a better study design. The investigators take your advice and hire you to help them design a new prospective cohort study. They want to know what type of cohort they should use to assemble the exposed population. Which type of cohort is the best for this situation?
a. Special cohort
b. Case cohort
c. General cohort
d. Experimental cohort

 

QUESTION 11

  1. In 2013, the number of new cases of influenza was 250 in Somerville and 1,075 in Boston. Which city had a higher cumulative incidence of influenza in 2013?
a. Somerville
b. Boston
c. Can’t be determined based on the information given

 

QUESTION 12

  1. A report of a clinical trial of a new drug versus a placebo noted that the new drug gave a higher proportion of successes than did the placebo (70% versus 40%). The report ended with the statement that the p value associated with this finding was equal to 0.05. This means that 5 out of 100 patients did not benefit from the new drug.

True

False

 

QUESTION 13

  1. Below is a chart of the natural history of disease for one individual:

Years
————————————>

A B C D E F

Key:
A = Biological onset
B = Disease detectable by screening
C = Individual’s disease was detected by screening, the diagnosis was made, and treatment was begun.
D = Clinical symptoms would have developed if the individual was not screened
E = Death would have occurred due to the disease if the individual had not been screened and treated
F = Death actually occurred

Which letters of the diagram are associated with the starting and stopping points for the lead time for this individual?

a. B to D
b. C to D
c. B to C
d. A to C

 

QUESTION 14

  1. The ideal comparison group in a cohort study…
a. Is as similar as possible to the exposed group with respect to other factors that could influence the development of disease.
b. Would, if possible, consist of exactly the same individuals in the exposed group had they not been exposed.
c. Both of the above
d. Neither of the above

 

QUESTION 15

  1. What is the main limitation of a case series?
a. It is difficult to find an adequate exposure group.
b. There is no explicit comparison group.
c. It measures effects at the population, not the individual, level.
d. It is difficult to obtain approval to conduct these studies.

 

QUESTION 16

  1. When assessing the results of a study, what are the possible explanations for the observed results? (CHOOSE ALLTHAT APPLY)
a. The observed results may be due to chance (i.e., random error)
b. The observed results may be true
c. The observed results may be due to bias
d. The observed results may be due to confounding

 

QUESTION 17

  1. Non-compliance in an experimental study biases the results towards the null.

True

False

 

QUESTION 18

  1. Which measure of disease frequency best describes the following: the percentage of nursing home residents who have bed sores on July 1, 2012.
a. Prevalence
b. Cumulative incidence
c. Incidence rate
d. None of the above

 

QUESTION 19

  1. A cohort study of coffee drinking and anxiety was conducted at a university campus. There were a total of 30,000 freshmen who participated. 10,000 were coffee drinkers and 20,000 were not. Of the coffee drinkers, 500 developed anxiety during the 4 year follow-up period. Of the non-coffee drinkers, 200 developed anxiety during the same time period. Assume that no one in the population died or was lost during the follow-up period. Calculate the risk ratio (a.k.a. relative risk) using the given data. The numeric value of the risk ratio is…
a. 1.0
b. 0.2
c. 5.0
d. None of the above

 

QUESTION 20

  1. Suppose that an experimental study investigator randomized 100 men to the treatment group and 100 men to the comparison group. However, only 75 men in the treatment group and 85 men in the comparison group were able to comply exactly with their assigned regimens. Should the data analysis be based on the 200 men originally randomized or the 160 men who were able to comply? Choose the best answer.
a. The 200 men who were originally randomized should be analyzed because the benefits of randomization will be preserved.
b. The 160 men should be analyzed because they represent the true effects of the treatment.
c. The 200 men who were originally randomized should be analyzed because they represent the entire study population.
d. The 160 men should be analyzed because they represent an intent-to-treat analysis.

 

QUESTION 21

  1. Suppose that your company has just developed a new screening test for a disease and you are in charge of testing its validity and feasibility. You decide to evaluate the test on 1000 individuals and compare the results of the new test to the gold standard. You know the prevalence of disease in your population is 30%. The screening test gave a positive result for 292 individuals. 285 of these individuals actually had the disease on the basis of the gold standard determination. Calculate the specificity of the new screening test:
a. 95%
b. 97.6%
c. 93.7%
d. 99%

   

QUESTION 22

  1. A study was conducted on the relationship between folic acid supplementation during pregnancy and the risk of having a child with a neural tube defect. The risk ratio comparing supplemented versus non-supplemented women was 0.33. This means that women who take folic acid were 67% less likely to have a child with a neural tube defect.

True

False

  

QUESTION 23

  1. A case-control study was conducted to identify risk factors for the common cold. Living with children under the age of 10 was one of the risk factors evaluated. The odds ratio for this association was 9.0 and the 95% confidence interval ranged from 1.2 to 85. Which of the following statements is true about this association? Choose all that apply.
a. People who lived with a child under the age of 10 had 9 times the risk of getting a cold compared to people who did not live with children under the age of 10.
b. The “p-value” was greater than 0.05.
c. The “p-value” was less than 0.05.
d. The association was statistically significant.
e. The true strength of association could be estimated more precisely if the study were repeated with a larger sample.

 

QUESTION 24

  1. Which of the following is an example of a “fixed” population?
a. The patient population of Boston Medical Center
b. Spring 2012 graduates of BUSPH
c. The residents of the City of Cambridge
d. The student body of BUSPH

  

QUESTION 25

  1. What type of observational study design is best suited to study a disease that has a long latent and induction period? (CHOOSE ALLTHAT APPLY)
a. Case-control study
b. Retrospective cohort study
c. Cross-sectional study
d. Prospective cohort study

   

QUESTION 26

  1. Suppose that we undertake a cohort study to examine the association of high salt intake and hypertension. Our study population consists of male and female Hispanics and Caucasians. No matching or restriction is performed. Let’s assume that the following facts are true: Men consume more salt than women. Irrespective of their salt consumption, men have a greater risk of developing hypertension than women. Smokers consume the same amount of salt as non-smokers. Smoking is an independent risk factor for hypertension. Hispanics consume more salt than Caucasians. Irrespective of their salt consumption , Hispanics have the same risk of hypertension as Caucasians. Based on the above information, which of the following are likely confounders in this study?
a. Gender
b. Smoking
c. Race/ethnicity
d. All of the above

  

QUESTION 27

  1. The purpose of a control group in a case-control study is to provide an estimate of the exposure distribution in the source population that produced the cases.

True

False

   

QUESTION 28

  1. Investigators began a study in 1995 to evaluate the association between infertility treatment and ovarian cancer occurrence among 3,000 Rhode Island women treated for infertility between 1984 and 1994. Cancer incidence was determined by matching the women to information in the Rhode Island Cancer Registry. The cancer rates in this sample were compared with cancer rates among the population of Rhode Island women. What kind of cohort study is this?
a. Retrospective
b. Prospective
c. Ambidirectional

 

QUESTION 29

  1. A cohort study of coffee drinking and anxiety was conducted at a university campus. There were a total of 30,000 freshmen who participated. 10,000 were coffee drinkers and 20,000 were not. Of the coffee drinkers, 500 developed anxiety during the 4 year follow-up period. Of the non-coffee drinkers, 200 developed anxiety during the same time period. Assume that no one in the population died or was lost during the follow-up period. Which of the following is the correct interpretation of a risk ratio calculated from this study?
a. Coffee drinkers are “x” times as likely to develop anxiety as compared to non-coffee drinkers.
b. The excess risk of anxiety among coffee drinkers is “x” as compared to non-coffee drinkers.
c. The excess risk of anxiety among the entire freshmen population is “x”
d. None of the above

  

QUESTION 30

  1. In an experimental study design, when the study participants do not know if they are in the treatment or comparison group but the investigators do, this is called a:
a. Double-blinded study
b. Single-blinded study
c. Equipoise study
d. Intent-to-treat study

 

QUESTION 31

  1. Length bias occurs because fast growing tumors are more likely to be picked up by a screening test than are slow growing tumors.

True

False

   

QUESTION 32

  1. What would happen to the predictive value positive if a screening test were administered in a population with a disease prevalence of 1% instead of 30%? (Assume that the sensitivity and specificity of the test remain the same.)
a. The predictive value positive would remain the same.
b. The predictive value positive would increase.
c. The predictive value positive would decrease.
d. It is impossible to tell from the information given.

  

QUESTION 33

  1. A population of 1,000 healthy, at risk people is monitored for one year starting on January 1st and the development of chicken pox cases is noted. No one has chicken pox at the start of the investigation. Twenty people develop chicken pox on June 30th and forty people develop chicken pox on September 30th. Twenty-four people were lost to follow-up on March 31st and twenty-four people were lost to follow-up on November 30th. None of those lost to follow-up had developed chicken pox prior to becoming lost. Assume that you can get chicken pox only once. What is the incidence rateof chicken pox in this population during the one-year period from January 1st through December 31st?
a. 60/1,000 person-years
b. 60/892 person-years
c. 60/992 person-years
d. 60/960 person-years

  

QUESTION 34

  1. Suppose that you began a one-year study of tuberculosis (TB) on January 1st, 2013. You enrolled 500 residents in your study and checked on their TB status on a monthly basis. At the start of your study on January 1st, you screened all 500 residents. 30 residents already had existing cases of TB on January 1st. On February 1st, 5 residents developed TB. On April 1st, 5 more residents developed TB. On July 1st, 10 of the residents who had existing TB on January 1stdied from their disease. The study ended on December 31, 2010. Assume that once a person gets TB, they have it for the duration of the study, and assume that all remaining residents stayed healthy and were not lost to follow-up.  What was the case-fatality rate among residents with TB over the course of the year?
a. 0%
b. 25%
c. 50%
d. 100%

 

QUESTION 35

  1. A study followed 900,000 US adults from 1992 to 2008. At baseline, all participants were screened and determined to be cancer free and their body mass index (BMI) was calculated. Body mass index is a measure of obesity that is calculated using a person’s height and weight. Subjects were separated into the following groups according to their BMI: (a) normal weight, (b) slightly overweight, (c) moderately overweight and (d) greatly overweight. 57,145 deaths from cancer occurred in the population during the follow-up period. What type of study is this?
a. Cohort study
b. Cross-sectional study
c. Case-control study
d. Ecologic study

 

QUESTION 36

  1. A cohort study was conducted to examine cigarette smoking and the risk of oral cancer. The investigators selected exposed and unexposed subjects so that they had the exactly same distribution of race. This method to address confounding by race is called:
a. Restriction
b. Stratification
c. Matching
d. None of the above

 

QUESTION 37

  1. Which measure of association is commonly used by public health officials to determine which exposures are most important to the entire population and helps prioritize prevention activities?
a. Risk/Rate ratio (a.k.a. relative risk)
b. Risk/Rate difference
c. Population risk/rate difference
d. None of the above

 

QUESTION 38

  1. State which of the following commonly used measures of disease frequency are TRUErates.
a. Case fatality rate
b. Attack rate
c. Survival rate
d. None of the above

 

QUESTION 39

  1. Which type of measure of disease frequency best describes the following: the percentage of healthy, at-risk children in a daycare who develop impetigo (a skin disease) during March 2012.
a. Prevalence
b. Incidence rate
c. Cumulative incidence
d. None of the above

 

QUESTION 40

  1. When a new prevention measure for a disease is developed, both the incidence and prevalence of the disease will decrease over the long term.

True

False

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