PUBH 401 practice quiz 4
The interval between the earlier period of diagnosis, made possible by the screening test, and the later usual time of diagnosis of a disease is called the lead time.
True
Using the Median Survival Time to assess disease prognosis, we only observe the deaths of half of the subjects under observation or treatment.
True
Which of the following statements is not the accurate description of selection bias in case-control studies?
Using hospitalized patients as controls is the best way to characterize the reference population because they are a captive population and are clearly identified.
In a natural history of disease in a patient, which of the following represents the preclinical face of the disease?
- Biological onset of the disease - Pathologic evidence of the disease if sought - Signs and symptoms of the disease
California Health Department wishes to assess the prognosis of infections diseases in the state. Which of the following can would you recommend as a measure of prognosis of a disease?
- Case-Fatality - 5-year Survival - Observed Survival - Median Survival Time - Relative Survival
To study the natural history of any given disease prognosis and treatment, which of the following can be considered as the outcome?
- Cure - Control - Disability - Death
If Relative Survival is greater than 1, what would be the interpretation of it?
- The observed survival exceeds the expected survival. - The observe survival increases more than the increase in the expected survival.
In a case-control study, which of the following is true?
- The proportion of cases with the exposure is compared with the proportion of controls with the exposure - The investigator may choose to have multiple comparison groups - Recall bias is a potential problem
The following is/are the problem(s) or reason(s) why 5-year survival may not be an appropriate measure for disease prognosis.
- There is a potential lead time bias. - Patients diagnosed less than five years age may not me well accounted for.
The chance or probability that a person tested negative truly does not has the disease is known as the Negative Predictive Value (NPV). Which of the following is used to calculate NPV?
- True Negatives - Number of test negatives
In calculating the life table, persons for whom data are not available for the full period of follow-up, either because follow-up was not possible or because they were enrolled after the study was started—are called
- withdrawals - losses to follow-up - censored observations
What proportion or percentage of patients were alive during the third 12 months of treatment?
0.018 OR 1.8%
What is the cumulative probability of surviving to the end of the 4-year follow-up period? Use the following table to answer the question.
0.06
The following table describes the survival of patients treated from disease X from 2015 to 2017 followed for 3 years (assuming no loss to follow-up). If a person is treated and using all the information from the table, what is the probability of surviving 3 years after treatment?
0.29
What is the probability that a person enrolled in the study will survive to the end of the second year?
0.317 OR 31.7%
What is the prevalence of HIV?
0.38%
What proportion of patients died during the first 12 months of treatment?
0.409 OR 40.9%
What proportion of patients died during the second 12 months of treatment?
0.464 OR 46.4%
What proportion or percentage of patients were alive during the second 12 months of treatment?
0.536 OR 53.6%
What proportion or percentage of patients were alive during 1-12 months of treatment?
0.591 OR 59.1%
What is the probability that a person enrolled in the study will survive to the end of the third year?
0.6% OR 0.006
What is the probability of those who did not die during the 25- to 36-month interval? Use the following table to answer the question.
0.67
The following table describes the survival of patients treated from disease X from 2015 to 2017 followed for 3 years (assuming no loss to follow-up). What was the probability of surviving the third year?
0.71
What proportion of patients died during the 25-36 months of treatment?
0.982 OR 98.2%
For those people who survived the second year, what is the probability of dying in the third year?
0.982 or 98.2%
The results of a blood pressure test for diabetes by two examiners observing the same test result are given in the table below. How many test positives do the two examiners agree on (Calculate A)?
10
What is the Negative predictive value (NPV) for the new rapid test for HIV in this cohort?
100%
The table given below shows the results of an x-ray result observed and reported by two radiologists. To assess the reliability of the result there is the need to know the percent of agreement between the two examiners. What is the expected agreement of the test positives, A?
108.91
What is the effective number exposed to risk of dying in the second year?
118.5
What is the effective number exposed to risk of dying in the 13- to 24-month interval? Use the following table to answer the question.
135
What is the effective number exposed to risk of dying in the first year?
234.5
The results of a blood pressure test for diabetes by two examiners observing the same test result are given in the table below. How many test negatives do the two examiners agree on (Calculate B)?
45
What is the Positive predictive value (PPV) for the new rapid test for HIV in this cohort?
48.7%
The table given below shows the results of an x-ray result observed and reported by two radiologists. To assess the reliability of the result there is the need to know the percent of agreement between the two examiners. What is the expected agreement of the test negatives, D?
50.91
In reading a screening test result by two observers, the expected agreement by chance for both positive and negative tests are given by 105.56 and 53.34, respectively. If the total reading of the result is 309. What is the percent agreement expected by chance by the two observers?
51.4%
A total of 180 patients were treated for disease X from 2012 to 2014, and their progress was followed to 2015. The treatment results are given in the table. No patients were lost to follow-up.1 What is the probability of surviving for 3 years? ______
54.8%
The results of a blood pressure test for diabetes by two examiners observing the same test result are given in the table below. What is the percent agreement of the test results by the two examiners?
55%
The observed agreement of non-dense and dense by two screening test examiners reading a synthetic 2D mammography are 11 and 14, respectively. If the observations by the examiners are independent and the total dense and non-dense by one of the examiners is 27 and 18, respectively. What is the percent agreement observed by the two examiners?
55.6%
What is the effective number exposed to risk of dying in the third year?
56
Two observers of a screening test came to a certain agreement on the reading of the results. Assume the observed percent agreement is 90% and the expected percent agreement by chance is 50%. As an epidemiologist, you decided to use Kappa Statistic to measure the reliability of the screening test. What is the value of the Kappa Statistic?
80%
Two observers of a screening test came to a certain agreement on the reading of the results. Assume the observed percent agreement is 91.9% and the expected percent agreement by chance is 51.4%. As an epidemiologist, you decided to use Kappa Statistic to measure the reliability of the screening test. What is the value of the Kappa Statistic?
83.3%
The table given below shows the results of two examiners of an x-ray result. To assess the reliability of the result there is the need to know the percent of agreement between the two examiners. What is the percent agreement of the test?
89.97%
The observed agreement of non-dense and dense by two screening test examiners reading a synthetic 2D mammography are 168 and 116, respectively. If the observations by the examiners are independent and the total dense and non-dense by one of the examiners is 127 and 182, respectively. What is the percent agreement observed by the two examiners?
91.9%
The table below shows the results from looking at the diagnostic accuracy of a new rapid test for HIV in 100,000 subjects, compared to the Reference standard ELISA test. The rows of the table represent the test result and the columns the true disease status (as confirmed by ELISA). What is the Sensitivity of the new rapid test for HIV?
99.5%
What is the Specificity of the new rapid test for HIV?
99.6%
In a cohort study, the advantage of starting by selecting a defined population for study before any of its members become exposed, rather than starting by selecting exposed and unexposed individuals, is that:
A number of exposures can be studied simultaneously
In a study begun in 1965, a group of 3,000 adults in Baltimore were asked about alcohol consumption. The occurrence of cases of cancer between 1981 and 1995 was studied in this group. This is an example of:
A prospective cohort study
The physical examination records of the entire incoming freshman class of 1935 at the University of Minnesota were examined in 1977 to see if their recorded height and weight at the time of admission to the university was related to the development of coronary heart disease (CHD) by 1986. This is an example of:
A retrospective cohort study
A group of physicians working in the same hospital noticed a rare presentation of male young patients, free of typical risks factors, who presented to the hospital with rapidly progressing acute kidney failure. They documented their findings and described in detail the progression of disease. What is the study design described here?
Case series
In a small pilot study, 12 women with endometrial cancer (cancer of the uterus) and 12 women with no apparent disease were contacted and asked whether they had ever used estrogen. Each woman with cancer was matched by age, race, weight, and parity to a woman without disease. What kind of study design is this?
Case-control study
They performed an epidemiologic study of 100 patients with newly diagnosed oropharyngeal cancer and 200 control patients without cancer to evaluate associations between HPV infection and oropharyngeal cancer. [D'souza G, Kreimer AR, Viscidi R, et al. A study of human papillomavirus and oropharyngeal cancer. N Engl J Med. 2007;356(19):1944-1956.] What kind of study design is this?
Case-control study
Which term most accurately describes the following definition? "The observational epidemiological study of persons with the disease (or another outcome variable) of interest and a suitable control group of persons without the disease (comparison group, reference group)." [Porta M, ed. A Dictionary of Epidemiology. New York: Oxford University Press; 2014.]
Case-control study
In which one of the following types of study designs does a subject serve as his own control?
Case-crossover study
Which of the following is a good index of the severity of a short-term, acute disease?
Case-fatality
In which of the following study designs is possible to calculate incidence rate?
Cohort
To determine the prevalence of smoking among new students in a university, researchers conduct an anonymous survey at the first day of classes. They find that 22% of women and 28% of men were smokers. What type of study design was used?
Cross-sectional
Residents of three villages with three different types of water supply were asked to participate in a survey to identify cholera carriers. Because several cholera deaths had occurred recently, virtually everyone present at the time underwent examination. The proportion of residents in each village who were carriers was computed and compared. What is the proper classification for this study?
Cross-sectional study
They analyzed the data according to the number of morbidities, disorder type (physical or mental), sex, age, and socioeconomic status. They defined multimorbidity as the presence of two or more disorders. [From Barnett K, Mercer SW, Norbury M, et al. Epidemiology of multimorbidity and implications for health care, research, and medical education. Lancet. 2012;380(9836):37-43.] What is the proper classification for this study?
Cross-sectional study
Which term most accurately describes the following definition? "A study that examines the relationship between diseases (or other health outcomes) and other variables of interest as they exist in a defined population at one particular time." [Porta M, ed. A Dictionary of Epidemiology. New York: Oxford University Press; 2014.]
Cross-sectional study
A researcher study of Baltimore's neighborhoods showed that those neighborhoods with lower median household income experienced a higher teen pregnancy rate. What type of study design was used?
Ecologic
A researcher study of Baltimore neighborhoods showed that those with lower median household income experience a higher teen pregnancy rate. After reading this, someone concludes that a teenager with low income is more likely to get pregnant. What is the name of this mistaken conclusion?
Ecologic fallacy
Which term most accurately describes the following definition? "Analysis based on aggregated or grouped data; errors in inference may result because associations may be artifactually created or masked by the aggregation process." [Porta M, ed. A Dictionary of Epidemiology. New York: Oxford University Press; 2014.]
Ecologic study
In contrast to the life table approach is the Kaplan-Meier (KM) method, where predetermined intervals are used.
False
The result of a screening test can still be considered highly useful and reliable if the sensitivity and specificity are high, but the results cannot be replicated.
False
When the reliability of a screening test is poor, the validity of the test can be good.
False
A case-control study is characterized by all of the following except:
Incidence rates may be computed directly
Two pathologists looking at one tumor biopsy gave two different results. What type of variation will likely affect the reliability of the biopsy results?
Interobserver Variation
A radiologist read an x-ray twice coming out with two different readings. What type of variation between the two readings could affect the reliability of the test?
Intraobserver Variation
Which of the following is not an advantage of a prospective cohort study?
It usually costs less than a case-control study
Which of the following is a true conclusion concerning matching?
Matching on many variables may make it difficult to find an appropriate control
A total of 180 patients were treated for disease X from 2012 to 2014, and their progress was followed to 2015. The treatment results are given in the table. No patients were lost to follow-up. An important assumption in this type of analysis is that:
No change has occurred in the effectiveness of the treatment during the period of the study
Which of the following is a case-control study?
Obtaining histories and other information from a group of known cases and from a comparison group to determine the relative frequency of a characteristic or exposure under study
A clinician conducted a screening test of lung cancer. At the end of the test, he wants to find the chance or probability that a person who tested positive truly has the disease. What statistic must he compute?
Positive Predictive Value (PPV)
The Baltimore Longitudinal Study of Aging (BLSA) is a research study of normative aging started in the 1950s. Volunteers, free of chronic conditions, are recruited and followed every 4, 2, or 1 year(s) until their death. What type of study design is this?
Prospective cohort
Baseline examination in 1973 determined cases of cardiovascular disease, behavioral and biologic risks, and stressful characteristics of work. Follow-up examinations included measurement of blood pressure, cholesterol concentration, and body mass index in 1978 and in 1983. [Kivimäki M, Leino-Arjas P, Luukkonen R, et al. Work stress and risk of cardiovascular mortality: a study of industrial employees. BMJ 2002;325(7369):857.] What kind of study design is this?
Prospective cohort study
Epidemiologists are studying the possible relationship of cholera infections to drinking water. They conduct a case-control study and interview patients with cholera infection (cases) and persons without cholera infection (controls). A patient who was diagnosed with cholera often tries to identify all kinds of information related to drinking water. However, controls who were not diagnosed with cholera may not remember water they drink which is not from an unhygienic source.
Recall bias
A major problem resulting from the lack of randomization in a cohort study is:
The possibility that a factor that led to the exposure, rather than the exposure itself, might have caused the disease
In 2010, investigators were interested in studying early-adult obesity as a risk factor for cancer mortality. The investigators obtained physician health reports on students who attended the University of Glasgow between 1948 and 1968. These reports included records of the students' heights and weights at the time they attended the university. The students were then followed through 2010. Mortality information was obtained using death certificates. This study can best be described as a:
Retrospective cohort
In 2018 a researcher from University U decided to conduct a study in which she investigated the association between hearing loss and suffering a war injury. What type of study design is being illustrated in this example?
Retrospective cohort study
A diagnostic test has been introduced that will detect a certain disease 1 year earlier than it is usually detected. Which of the following is most likely to happen to the disease within the 10 years after the test is introduced? (Assume that early detection has no effect on the natural history of the disease. Also, assume that no changes in death certification practices occur during the 10 years.)
The apparent 5-year survival will increase
In cohort studies of the role of a suspected factor in the etiology of a disease, it is essential that:
The exposed and unexposed groups under study be as similar as possible with regard to possible confounding factors
A researcher wants to investigate if tea consumption (assessed by a biomarker for tea metabolism) increases the risk of CHD. He uses a case-control study to answer this question. CHD is rare in younger people. Which two groups are best to enroll and compare for this purpose?
The group of CHD cases and a group of those who do not develop CHD, matched for age
Which of the following statements is the most accurate characteristic of cohort studies?
The incidence rate of disease in the exposure group is compared directly to the incidence rate of disease in the unexposed group.
Retrospective cohort studies are characterized by all of the following except:
The required sample size is smaller than that needed for a prospective cohort study
What is the most important assumption in this type of analysis? Use the following table to answer the question.
There has been no secular (temporal) change in the effectiveness of treatment or in survivorship over calendar time.
Which of the following illustrates a violation to one of the assumptions made when using the Kaplan-Meier method?
There is a significant improvement in the treatment of the condition being studied in the middle of the duration of the study.
Two observers of a screening test came to a certain agreement on the reading of the results. Assume the observed percent agreement and the expected percent agreement by chance were obtained. As an epidemiologist, you decided to use Kappa Statistic to measure the reliability of the screening test. You computed the Kappa statistic and obtained 50%. How would you interpret this value?
There is an an intermediate or good agreement between the observers.
Children with brain tumors were compared with two groups of controls: The first control group, called normal controls, consisted of children with no known malignant disease. The second control group, called cancer controls, consisted of children with malignancies other than brain tumors. What is the benefit of using multiple controls in case-control studies?
This may reduce the recall bias from participants.
Before reporting the results of this survival analysis, the investigators compared the baseline characteristics of the 42persons who withdrew from the study before its end with those of the participants who had complete follow-up. This was done for which of the following reasons:
To check whether those who remained in the study represent the total study population
What would be the interpretation for a Kappa statistic value of 0.80?
excellent agreement between the observers.
The following are assumptions for the application of the Kaplan Meier method of survival analysis, except
predetermined intervals are used.
The main difference between a cohort study and a randomized trial is that
randomized trials are experimental and cohort studies are observational.
