Block 9 Epidemiology Part 2 MCQ's

1. You would typically use a descriptive study

For a comparison between a new SSR1 drug and Venlafaxine

To document a cluster of Wegener's granulomatosis cases that has recently appeared in your area

To evaluate the effects of Team Based Learning (TBL) versus didactic lecture

None of the above

A descriptive study is typically used to document and describe a phenomenon or situation. In this case, the study is focused on documenting a cluster of Wegener's granulomatosis cases that have recently appeared in the area. The study aims to gather information about the cases, their characteristics, and any potential patterns or trends. This type of study would not involve comparing different treatments or assessing efficacy, but rather collecting data to better understand the occurrence of the disease in the area.

Explanation

A descriptive study is typically used to document and describe a phenomenon or situation. In this case, the study is focused on documenting a cluster of Wegener's granulomatosis cases that have recently appeared in the area. The study aims to gather information about the cases, their characteristics, and any potential patterns or trends. This type of study would not involve comparing different treatments or assessing efficacy, but rather collecting data to better understand the occurrence of the disease in the area.

2. Reliability can be defined as:

The degree to which an instrument measures what it is supposed to measure

The degree to which results are consistent

A measure of the degree or strength of association between two variables

Concerned with measuring the frequency of new cases with reliability

Ensuring that patients all take a test under the same conditions

The correct answer is "the degree to which results are consistent". Reliability refers to the consistency of results obtained from a measurement or assessment tool. In other words, it measures the extent to which the same results can be obtained repeatedly under the same conditions. A reliable instrument or test will produce consistent and stable results over time, indicating that it is measuring the same construct consistently. Reliability is an important aspect of any measurement or assessment tool as it ensures that the results obtained are dependable and trustworthy.

Explanation

The correct answer is "the degree to which results are consistent". Reliability refers to the consistency of results obtained from a measurement or assessment tool. In other words, it measures the extent to which the same results can be obtained repeatedly under the same conditions. A reliable instrument or test will produce consistent and stable results over time, indicating that it is measuring the same construct consistently. Reliability is an important aspect of any measurement or assessment tool as it ensures that the results obtained are dependable and trustworthy.

3. In 1945, there were 1,000 women who worked in a factory painting radium dials on watches. The incidence of bone cancer in these women up to 1975 was compared with that of 1,000 women who worked as telephone operators in 1975. Twenty of the radium dial painters and four of the telephone operators developed bone cancer between 1945 and 1975. This study is an example of a:

Experimental study

Case series

Clinical trial

Retrospective cohort study

Case-control study

This study is an example of a retrospective cohort study because it follows a group of individuals (the radium dial painters) over a period of time (from 1945 to 1975) to compare their incidence of bone cancer with another group (the telephone operators). The study design allows for the observation of bone cancer development in both groups and the comparison of their outcomes.

Explanation

This study is an example of a retrospective cohort study because it follows a group of individuals (the radium dial painters) over a period of time (from 1945 to 1975) to compare their incidence of bone cancer with another group (the telephone operators). The study design allows for the observation of bone cancer development in both groups and the comparison of their outcomes.

4. A comparison of clinically diagnosed versus autopsy-confirmed gastric and peptic ulcers was performed or 100„000 consecutive diseased patients in several large hospitals as shown in the following table,

From these data, the sensitivity of clinical diagnosis was:

1,500/1700

200/96,000

95,800/96,000

1,500/4,000

2,500/4,000

The sensitivity of clinical diagnosis was calculated by dividing the number of clinically diagnosed cases of gastric and peptic ulcers (1,500) by the total number of autopsy-confirmed cases (4,000). This gives us the proportion of true positive cases that were correctly identified by the clinical diagnosis.

Explanation

The sensitivity of clinical diagnosis was calculated by dividing the number of clinically diagnosed cases of gastric and peptic ulcers (1,500) by the total number of autopsy-confirmed cases (4,000). This gives us the proportion of true positive cases that were correctly identified by the clinical diagnosis.

5. The following table gives the results of a screening test for diabetes compared to a confirmatory evaluation (oral glucose tolerance test).

The sensitivity of this screening test for diagnosing diabetes is:

23%

29%

63%

99%

100%

The sensitivity of a test is calculated as the proportion of true positive results (diabetic individuals correctly identified by the test) out of all actual positive cases (both correctly identified and missed by the test).

From the table in the image, we have:

True Positive (correctly identified as diabetic): 34

False Negative (incorrectly identified as not diabetic): 116

We can calculate the sensitivity using the formula:

Sensitivity = {True Positive}/{True Positive} +{False Negative}}

Substituting the values:

Sensitivity = 34/34 + 116 = 34/150 ≈ 0.23

So, the sensitivity of this screening test for diagnosing diabetes is approximately 23%. Therefore, the correct answer is 23%.

Explanation

The sensitivity of a test is calculated as the proportion of true positive results (diabetic individuals correctly identified by the test) out of all actual positive cases (both correctly identified and missed by the test).

From the table in the image, we have:

True Positive (correctly identified as diabetic): 34

False Negative (incorrectly identified as not diabetic): 116

We can calculate the sensitivity using the formula:

Sensitivity = {True Positive}/{True Positive} +{False Negative}}

Substituting the values:

Sensitivity = 34/34 + 116 = 34/150 ≈ 0.23

So, the sensitivity of this screening test for diagnosing diabetes is approximately 23%. Therefore, the correct answer is 23%.

6. Validity can be defined as:

The degree to which an instrument measures what it is supposed to measure.

The degree to which results are consistent on a repeat measurement

A measure of the degree or strength of association between two variables.

Concerned with measuring the frequency of new cases with reliability

None of the above

Validity refers to the degree to which an instrument or measurement accurately measures what it is intended to measure. It assesses whether the instrument is measuring the specific construct or concept it claims to measure. In other words, it examines whether the instrument is valid for the purpose it is being used for. Validity is important in research and measurement as it ensures that the results obtained are meaningful and accurate.

Explanation

Validity refers to the degree to which an instrument or measurement accurately measures what it is intended to measure. It assesses whether the instrument is measuring the specific construct or concept it claims to measure. In other words, it examines whether the instrument is valid for the purpose it is being used for. Validity is important in research and measurement as it ensures that the results obtained are meaningful and accurate.

7. An outbreak of gastritis occurred on the Northern Star cruise ship traveling from New York to Nassau. The data in the table below was obtained from a questionnaire completed by everyone on board the ship shortly after the outbreak.

Data from an Outbreak of Gastritis on the Northern Star Cruise Shuzii

Given this information, what is the relative risk of developing gastritis from Shrimp and rice on the Northern Star Ship?

5.0

1.0

3.2

2,0

7.5

The relative risk of developing gastritis from Shrimp and rice on the Northern Star ship is 2.0. This is calculated by dividing the probability of developing gastritis among those who ate Shrimp and rice (200/1200) by the probability of developing gastritis among those who did not eat Shrimp and rice (100/1500). The result is 2.0, indicating that those who ate Shrimp and rice are twice as likely to develop gastritis compared to those who did not eat it.

Explanation

The relative risk of developing gastritis from Shrimp and rice on the Northern Star ship is 2.0. This is calculated by dividing the probability of developing gastritis among those who ate Shrimp and rice (200/1200) by the probability of developing gastritis among those who did not eat Shrimp and rice (100/1500). The result is 2.0, indicating that those who ate Shrimp and rice are twice as likely to develop gastritis compared to those who did not eat it.

8. An outbreak of gastritis occurred on a cruise ship. The data in the following table were obtained shortly after the outbreak from a questionnaire completed by everyone on board the ship. What is the relative risk of developing gastritis from herring consumption?

0:5

2:0

2:3

8:0

1:0

The relative risk of developing gastritis from herring consumption is 2.0. This means that individuals who consumed herring are twice as likely to develop gastritis compared to those who did not consume herring.

Explanation

The relative risk of developing gastritis from herring consumption is 2.0. This means that individuals who consumed herring are twice as likely to develop gastritis compared to those who did not consume herring.

9. Epidemic refers to

A disease that has a low rate of occurrence but that is constantly present in a community or region

An attack rate in excess of 10 per 1,000 population

Diseases of the respiratory system that occur seasonally

The annual case rate per 100,000 population

An epidemic refers to the occurrence of illness/illnesses of a similar nature, clearly in excess of the normal expectation for that population at that time. This means that there is a sudden increase in the number of cases of a particular disease or illness in a specific community or region, which is higher than what is typically expected. It is characterized by a higher-than-usual occurrence of a specific illness, indicating an outbreak or spread of the disease within a population.

Explanation

An epidemic refers to the occurrence of illness/illnesses of a similar nature, clearly in excess of the normal expectation for that population at that time. This means that there is a sudden increase in the number of cases of a particular disease or illness in a specific community or region, which is higher than what is typically expected. It is characterized by a higher-than-usual occurrence of a specific illness, indicating an outbreak or spread of the disease within a population.

10. You would typically use a descriptive study

For a comparison between a new SSRI drug and Venlafaxine

To document a cluster of Wegener's granulomatosis cases that has recently appeared in your area

To evaluate the effects of Team Based Learning (TBL) versus didactic lecture

None of the above

A descriptive study is typically used to document and describe a specific phenomenon or situation. In this case, documenting a cluster of Wegener's granulomatosis cases that has recently appeared in your area would require a descriptive study to gather information about the cases, analyze the data, and provide a detailed description of the cluster. This type of study would help in understanding the characteristics, prevalence, and potential causes of the disease cluster.

Explanation

A descriptive study is typically used to document and describe a specific phenomenon or situation. In this case, documenting a cluster of Wegener's granulomatosis cases that has recently appeared in your area would require a descriptive study to gather information about the cases, analyze the data, and provide a detailed description of the cluster. This type of study would help in understanding the characteristics, prevalence, and potential causes of the disease cluster.

11. Regionville is a community of 100,000 persons. During 1985 there were 1,000 deaths from all causes. All cases of tuberculosis have been found and they total 300 - 200 males and 100 females. During 1985, there were 60 deaths from tuberculosis, 50 of them males. The crude mortality rate for Regionville is

300 per 100,000

60 per 1,000

10 per 1,000

100 per 1,000

200 per 1,000

The crude mortality rate is calculated by dividing the number of deaths by the total population and then multiplying by a constant (usually 1,000 or 100,000) to express the rate per 1,000 or 100,000 people. In this case, there were 1,000 deaths in a population of 100,000. So, the crude mortality rate is 1,000/100,000 = 10 per 1,000.

Explanation

The crude mortality rate is calculated by dividing the number of deaths by the total population and then multiplying by a constant (usually 1,000 or 100,000) to express the rate per 1,000 or 100,000 people. In this case, there were 1,000 deaths in a population of 100,000. So, the crude mortality rate is 1,000/100,000 = 10 per 1,000.

12. A school district has been using an intelligence test to evaluate students and make important placement decisions, such as who gets placed into gifted and other special education settings. However, a group of psychologists advises the school district that there is a problem with this particular test. More specifically, the criticism is that scores on this test correlate too highly with students socioeconomic status. This criticism most directly suggests a problem with the test's:

Internal consistency

Test-retest reliability

Discriminant validity

Convergent validity

Predictive validity

The criticism that scores on the intelligence test correlate too highly with students' socioeconomic status suggests a problem with the test's discriminant validity. Discriminant validity refers to the ability of a test to distinguish between different constructs or variables. In this case, the test is not effectively distinguishing between intelligence and socioeconomic status, indicating a lack of discriminant validity.

Explanation

The criticism that scores on the intelligence test correlate too highly with students' socioeconomic status suggests a problem with the test's discriminant validity. Discriminant validity refers to the ability of a test to distinguish between different constructs or variables. In this case, the test is not effectively distinguishing between intelligence and socioeconomic status, indicating a lack of discriminant validity.

13. In a study of 500 cases of a disease and 500 controls, the suspected etiological factor is found in 400 cases and 100 controls. The absolute risk of disease in people with the factor is

Cannot be computed from the data given

80%

40%

16%

20%

In the study, the suspected etiological factor is found in:

400 out of 500 cases (individuals with the disease).

100 out of 500 controls (individuals without the disease).

To determine the absolute risk of the disease in people with the factor, you can calculate the ratio of cases with the factor to the total number of cases.

Absolute Risk = Number of cases with the factor / Total number of cases

Absolute Risk = 400 cases / 500 total cases

Absolute Risk = 0.8 or 80%

So, the absolute risk of the disease in people with the suspected etiological factor is 80%.

Explanation

In the study, the suspected etiological factor is found in:

400 out of 500 cases (individuals with the disease).

100 out of 500 controls (individuals without the disease).

To determine the absolute risk of the disease in people with the factor, you can calculate the ratio of cases with the factor to the total number of cases.

Absolute Risk = Number of cases with the factor / Total number of cases

Absolute Risk = 400 cases / 500 total cases

Absolute Risk = 0.8 or 80%

So, the absolute risk of the disease in people with the suspected etiological factor is 80%.

14. The following figure shows the epidemic curve for an outbreak of fever and rash among a group of children at a summer camp. They were exposed to a younger relative of one of the campers with fever and rash who had come to visit on the 9^{th •} ^{The average incubation period for the organism in this outbreak is}

8 days

12 days

16 days

20 days

To determine the average incubation period for the organism in the outbreak, we need to observe the time interval between the day of exposure and the peak of the epidemic curve. In the graph, the exposure is marked on the 9th, and the peak appears to be around the 17th day.

If we count the days from the 9th to the peak on the 17th:

17 - 9 = 8 days

So, the average incubation period for the organism in this outbreak appears to be 8 days. This is calculated based on the time when the largest group of children started showing symptoms, assuming the most common incubation period will align with this peak in cases.

Explanation

To determine the average incubation period for the organism in the outbreak, we need to observe the time interval between the day of exposure and the peak of the epidemic curve. In the graph, the exposure is marked on the 9th, and the peak appears to be around the 17th day.

If we count the days from the 9th to the peak on the 17th:

17 - 9 = 8 days

So, the average incubation period for the organism in this outbreak appears to be 8 days. This is calculated based on the time when the largest group of children started showing symptoms, assuming the most common incubation period will align with this peak in cases.

15. The mean birth weight of first-born infants of 23 women who smoked more than one pack of cigarettes per day during pregnancy was 200 g lower than those of the first-born infants of 16 women who never smoked, The difference was statistically significant at the 5% level (P<0,05). This means which of the following?

Smoking during pregnancy retards fetal growth

The difference observed between mean birth weights was too large to have occurred by chance alone

The difference observed between mean birth weights could have been easily occurred by chance alone

The number of patients studied was not sufficient to achieve a conclusive result

Smoking during pregnancy does not influence fetal growth

The given information states that the mean birth weight of infants born to women who smoked heavily during pregnancy was significantly lower than those born to women who never smoked. This suggests that smoking during pregnancy retards fetal growth. The fact that the difference in birth weights was statistically significant at the 5% level indicates that it is unlikely to have occurred by chance alone. Therefore, the correct answer is that the difference observed between mean birth weights was too large to have occurred by chance alone.

Explanation

The given information states that the mean birth weight of infants born to women who smoked heavily during pregnancy was significantly lower than those born to women who never smoked. This suggests that smoking during pregnancy retards fetal growth. The fact that the difference in birth weights was statistically significant at the 5% level indicates that it is unlikely to have occurred by chance alone. Therefore, the correct answer is that the difference observed between mean birth weights was too large to have occurred by chance alone.

16. California Highway Patrol statistics revealed that more accidents occurred to blue cars than to cars of any other color. The inference that while driving a blue car, one is at higher risk of an accident than while driving a car of another color is

Correct

Incorrect, because the comparison is not based on rates

Incorrect, because no control or comparison group is used

Incorrect, because no test of statistical significance has been made

Incorrect, because prevalence is used instead of incidence

The answer is B, because the statement only provides information about the number of accidents that occurred in blue cars compared to cars of other colors. It does not mention the rates or proportions of accidents for each color, which is necessary for making a valid comparison. Without considering the rates, it is not possible to determine whether driving a blue car actually puts one at a higher risk of an accident compared to driving a car of another color.

Explanation

The answer is B, because the statement only provides information about the number of accidents that occurred in blue cars compared to cars of other colors. It does not mention the rates or proportions of accidents for each color, which is necessary for making a valid comparison. Without considering the rates, it is not possible to determine whether driving a blue car actually puts one at a higher risk of an accident compared to driving a car of another color.