For each of the following statements, indicate whether the statistical association is likely the result of chance, bias, or confounding.
The association between Down Syndrome and birth order in a case control study would be confounding. The third factor is the age of the mother.
The case control study for chest radiographs during pregnancy would be by chance. Not every pregnant woman has breast cancer.
This was a case of chance. Since is was a randomized trial and the relative risk value is .35 and the 95% confidence interval is .14-55.01, this also suggests it was a case of chance. Not every drug will have this same effect.
Since there was no statistical data found between pancreatic cancer and smoking, and the relative risk was 1 and P is .85 it is a case of bias.
The case control study for the association of thromboembolism and use of oral contraceptives shows that it is a case of bias. The real truth between the association is not known and the doctors hospitalized the women to try to find the solution. Therefore, it is bias.
3. Recall the causal criteria presented by Sir Austin Bradford Hill in 1965. Discuss these criteria in the contest of smoking and lung cancer.
Sir Austin Bradford Hill in 1965 proposed nine points that are used to define if statistical associations were also causal associations. These are consistency of association, strength of association, specificity, biologic gradient, biological plausibility, experimental evidence, coherence, analogy, and temporality.
There is a strong statistical association between smoking (exposure) and lung cancer (disease). This shows that causal association is valid. Therefore the strength of association is related to smoking and lung cancer. The consistency of association is shown through investigators proving different conditions and situations that lung cancer is caused by smoking. The specificity of the case is shown due to most cases of lung cancer being associated with smoking history of individuals. People who smoke regularly often develop lung cancer in a few years. This proves the temporality in which the disease is caused after the exposure. The biological gradient of smoking to cause lung cancer is shown that as a habit of smoking increases, so does the chance of lung cancer. The biological plausibility is seen because in tobacco smoke, almost 60 known carcinogens are found. These are enough chemical agents to prove the biological plausibility. The coherence and association is shown since smoking causes lung cause that is regular with the known epidemiologic configurations and patterns. Analogy Criteria can be seen through similar reports previously stated that smoking leads to cancer. Finally, there are many experiments done which shows tobacco smoke contains carcinogens lead to malignant tumors or cancer. Hence this proves experimental evidence.
5. Match the following.
Predisposing factors: c
Enabling Factors: a
Precipitating Factors: b
Reinforcing Factors: d
7. Define and compare the differences between statistical inference and causal inference.
Statistical Inference: can be referred to as an assumption for a group of people or a population that are established on sampled information or data. With the help of this sample information and data one can make probability and guess the reports about the observation. Samples are chosen instead of whole population because they can be studied and evaluated faster and quicker. It is impossible to study a whole population of an area.
Causal Inference: An assumption which is made for the present health state or even and explanations for the existence of this state or event. The link between the human health and the environmental factors like the social , behavioral, biological, and psychosocial factors is generally related to the causal inference. There causal inferences give the scientific foundation for public and medical health actions.
There are two causal associations which are based on intermediate factor and its complexity. Direct causal association contains no intermediate factor and indirect causal association involves more intermediate factors and is generally more complicated.
9. A component cause is also called which of the following?
D. Each of the above
Chapter 10: Evens
2. Matching
A. Often synonymous with epidemics but is applied when the scope is limited= B outbreak
B. The occurrence of a disease…. A epidemic
C. An aggregation…. C Cluster
4. How would you classify an epidemic if the epidemic curve showed a rapid rise, peak, and gradual disease?
A point source epidemic. All individuals in the population come in contact with the causative agent over a small time period. This is a log-normal distribution, where the cases increase exponentially in number, reaching a peak and then gradually diminish. The incubation time varies among individual, which reflects differences in the exposure intensity and also in the different immune responses. Point source epidemics have some common source, such as an infected food handler or contaminated water or food resource, and all the exposure occurs in a very short amount of time.
6. Where might the epidemiologist search for cases that have not been identified?
They must examine various clinics, hospital emergency departments, physicians, migrant health clinics, and other such facilities to look for people have the disease in question. Evaluation of mild cases of the disease or the asymptomatic individuals and their contacts should be done. Individuals then must be placed into appropriate and separate categories, and the suspected cases must be separated from the probable cases.
8. What is the primary purpose of providing a final report in a field investigation?
The final report represents a narrative for the entire investigation process along with a review of the course of the studied epidemic as a case study. The data is represented in the form of graphs, charts, tables, etc. A good report will compare the test hypotheses with the established facts. Final reports are also very important in case of infectious diseases as they spread rapidly and therefore information must be presented as early as possible for schools, health offices, hospitals, etc.
10. List and describe the four stage process of a cluster investigation.
Initial Contact and Repose: Required to collect information about the suspected clusters being reported to the local health departments. The reported cases are taken very seriously. There are recommended procedures for this stage such as to obtain the caller ID and health evens, number of affected individuals, and the area/time of the disease. The identification of the affected people and the information about the time of follow-up regarding them should be recorded. All contacts should be recorded in a log book and the health officials should be notified.
Assessment: This stage is divided into 3 phases
Initial evaluation: determining whether the health problem is in excess or not, evaluation of the case that ensures that a biological basis present, and description of epidemiologic characteristics by further evaluation of either few or all the cases that are suspected.
Preliminary Evaluation: THe geographic area is determined along with the study’s time period. This is followed by ascertaining the cases under the established space-boundaries and time along with the identification of appropriate population for reference.
Major Feasibility: The stage is aimed at associating the excess numbers of cases with the suspected exposure. There are various steps in this stage. The health condition under consideration should be reviewed in the literature for any exposures that are putative. An appropriate study design must be selected and the cost attending, the size of sample, and the time/ area dimensions and the selection of a group as control should be considered.
Determination of the required control data and the case including physical and laboratory measurements should be done. The political, social climate, and impact of all decisions and their outcomes should be considered along with the resources that are required for the study. Hypotheses must be developed and supported by the data.
Etiologic Investigation: This is done to establish the effect of a relationship and cause through a standardized study approach. A final report must be produced that is the narrative of the course of investigation in clear terms.
12. Why are rates sometimes preferred to counts?
Rates are the number of events that occur in a defined period of time, divided by the average population at risk of that event. Rates are often used instead of counts because they allow comparison of the level of disease or another health event in two different populations. According to http://www.houstontx.gov/health/Epidemiology/epicorner-1-14-05.htm “For example, to compare the number of Salmonellosis cases reported in Houston with the number reported in another city, use rates and not counts. If two different cities both had 277 cases of Salmonellosis a year it may appear they have the same level of problem, but this may not be the case. See the figure below. This table compares two fictitious cities, one called Uoyba City and one called Notsouh. In scenario A both cities have 277 cases of Salmonellosis a year. In Scenario B, Uoyba City has over twice as many cases.â€
14. What is the primary distinction between a cluster and a sentinel health-related state or event?
Disease Cluster: the unusual aggregation or health issues that are grouped together in space and time and is reported to a health institution. It occurs when a physical stress, psychological condition or a biological agent is suddenly introduced into the human environment.
Sentinel Health-related State or event: the occurences of unexpected health issues which have clear, recognized causes and carry serious and adverse outcomes.