090013 Fundamentals of Epidemiology Assessment Answer

Question 1

A study investigated the association between work in occupations likely to have involved exposure to asbestos and the occurrence of malignant mesothelioma. Mesothelioma is a rare type of cancer that usually occurs in the chest cavity. The table shows the data for carpenters (the exposed) and people working in occupations thought to be at low risk of asbestos exposure (the unexposed). Assume nearly all carpenters were exposed to asbestos.

a) In this study, the appropriate measure to use to examine whether work as a carpenter (a proxy for exposure to asbestos) is associated with mesothelioma is an odds ratio. Can you explain why?

b) What is the numerical value and interpretation of this measure?

c) Can you calculate the attributable fraction? If so, calculate and interpret. If not, explain why not.

d) Can you calculate population attributable fraction? If so, calculate and interpret. If not, explain why not.

• A study investigated the association between work in occupations likely to have involved exposure to asbestos and the occurrence of malignant mesothelioma. Mesothelioma is a rare type of cancer that usually occurs in the chest cavity. The table shows the data for carpenters (the exposed) and people working in occupations thought to be at low risk of asbestos exposure (the unexposed). Assume nearly all carpenters were exposed to asbestos.

a) In this study, the appropriate measure to use to examine whether work as a carpenter (a proxy for exposure to asbestos) is associated with mesothelioma is an odds ratio. Can you explain why?

As a measure of the relative risk of an event occurring in two groups, the odds ratio may be used to investigate whether carpentry work is linked to mesothelioma.

The odds ratio in this example would be the comparison between the likelihood of a carpenter acquiring mesothelioma and the likelihood of someone in a different occupation developing mesothelioma. The odds ratio evaluates two groups by contrasting the likelihood of an event occurring in each. Probability quantifies how likely something is to happen.

Carpenter occupation and mesothelioma risk may be further investigated using the odds ratio. Because it compares the likelihood of an occurrence in one group to that of an occurrence in another, it may be used to draw conclusions about the relative importance of the two groups. The odds ratio in this situation would be the comparison between the risk of getting mesothelioma for a carpenter and the risk for someone in different employment.

b) What is the numerical value and interpretation of this measure?

The odds ratio has a numerical value of 3.24, which implies that the likelihood of a carpenter being diagnosed with mesothelioma is 3.24 times more likely than the likelihood of a person working in a different occupation being diagnosed with the illness.

This gives proof that there is a substantial association between working as a carpenter and the chance of acquiring mesothelioma in later life. Carpentry employment has been linked to an increased risk of the disease.

c) Can you calculate the attributable fraction? If so, calculate and interpret. If not, explain why not.

Attributable percentage = (odds ratio − 1) / odds ratio. The attributable fraction is the percentage of observed occurrences that can be directly linked to the investigated exposure.

The attributable fraction in this situation is 0.68, which suggests that 68 percent of mesotheliomas may be traced back to a career in carpentry.

The formula for calculating the attributable proportion is as follows:

AF = (3.24-1)/3.24 

AF = (3.24-1)/3.24 

AF = 0.68

As a result, 68 percent of mesotheliomas can be linked to a carpenter's job.

d) Can you calculate population attributable fraction? If so, calculate and interpret. If not, explain why not.

Prevalence of exposure can be used to determine the population attributable fraction. What this means is that the fraction of occurrences in the population that can be ascribed to the exposure is known as the population attributable fraction.

With a population attributable fraction of 0.17, we know that carpentry is responsible for 17% of all mesotheliomas.

Follow these steps to determine your population's share that you are responsible for:

PAF = P(E) * AF

PAF = 0.25 * 0.68

PAF = 0.17

This indicates that carpentry is directly responsible for 17% of all mesotheliomas diagnosed in the general population.

Question 2

A cohort study of people who were admitted to hospital for a stroke looked at the association between admission to hospital on weekdays (Monday to Friday) or the weekend (Saturday and Sunday) with in-hospital mortality. The data from the study are reported in Table 1 below. In this question, provide all working for your calculations.

Ans- 

A cohort study of people who were admitted to hospital for a stroke looked at the association between admission to hospital on weekdays (Monday to Friday) or the weekend (Saturday and Sunday) with in-hospital mortality. The data from the study are reported in Table 1 below. In this question, provide all working for your calculations.

Table 1: In-hospital mortality, by admission period (weekday or weekend), among people admitted to the hospital for a stroke

1. Calculate the risk ratio for in-hospital mortality to compare mortality by admission period. 

The risk ratio for death while in the hospital is:

2.467/5.929, which is 0.415

Persons admitted to the hospital on the weekends have a mortality risk that is 0.415 times higher than the risk of people admitted to the hospital during the weekdays. This implies that the danger of dying while in the hospital is higher overall.

2.What was the (absolute) difference in mortality rates by admission period? Interpret your

The difference in fatality rates across the different admission periods was 0.0247 in absolute terms. This indicates that the death rate on the weekend was 0.0247 times greater than the mortality rate during the weekdays.

3. Now calculate the attributable fraction associated with weekend admission. Give an interpretation of your.

The proportion of a patient's overall admissions that may be attributed to a weekend visit is:

0.0247/0.415 = 0.0596.

This indicates that the fact that a person was admitted to the hospital on a weekend is responsible for 5.96 percent of all fatalities that occurred among persons who were admitted to the hospital for a stroke.

4. Calculate the population attributable risk for weekend admissions. Give an interpretation of your

The risk to the population that is related to weekend admissions is:

0.0596*0.23297, which is 0.0138.

This indicates that the fact that patients were hospitalized over the weekend is responsible for 1.38% of all strokes that take place in the world.

5. Now calculate and interpret the population attributable fraction for weekend admissions.

The population attributable fraction for weekend admissions is calculated to be 0.0596.

 i.e., 0.0138/ 0.23297 = 0.0596

This indicates the fact that persons who were hospitalized over the weekend can be held responsible for 5.96 percent of all strokes that take place in the world.

6. Summarise the findings from 1 to 5 in a paragraph.

The results of this study indicate that persons who are admitted to the hospital for a stroke on the weekend have a greater chance of dying while they are being treated there compared to those who are admitted on a weekday. This disparity can be attributed to the fact that during the weekends there is less staff and access to fewer resources.

7. What further information would you wish to know to assess the validity of your conclusions?

The number of individuals who are admitted to the hospital for a stroke on a weekend, the number of people who die from a stroke on a weekend, and the number of people who die from a stroke on a weekday are all additional pieces of information that might help determine whether or not these findings are accurate.

The data are also available by age group, with 2x2 tables for those aged < 65 years and those aged 65 years or older (Table 5).

Table 2: In-hospital mortality, by admission period (weekday or weekend), among people admitted to the hospital for a stroke

• Age < 65 years

• Age ≥ 65 years

1. Calculate the stratum-specific risk ratios.

Those under the age of 65 have a risk ratio of 0.390/0.647, which equals 0.600 for death while in the hospital. This indicates that the chance of dying while in the hospital is 0.6 times higher for those who are hospitalized on the weekends than it is for persons who are admitted during the weekdays.

For patients ≥65 years old, the risk ratio for death while in the hospital is 2.077/5.282, which is 0.392. Persons admitted to the hospital on the weekends have a mortality risk that is 0.392 times higher than the risk of people admitted to the hospital during the weekdays. This implies that the chance of dying while in the hospital is significantly higher.

2. Using 1, discuss whether the age group is an effect modifier.

The answer is no; age does not have a role in modifying the effects.

There are several explanations for why age is not a moderator of effects. To begin with, both younger and older patients have comparable risk ratios for dying while hospitalized. This data demonstrates that the correlation between weekend hospital admission and subsequent death holds across all age groups. For another, there is an overlap in the confidence intervals for the risk ratios in the two age groups. This means that it is unclear if the real risk ratio is different for the two age groups. Thirdly, the risk ratios for both age groups do not have statistically significant p-values. This indicates that the evidence supporting a distinct risk ratio between tageges groups is insufficient. fourth, there was no statistically significant correlation between age group and weekend admittance. This indicates that there is no difference in the correlation between hospital admission on the weekend and subsequent fatality rates between the sexes.

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