Block 9 Epidemiology MCQ's

(Incidence/longitudinal/prospective study)
Starting point is definition of a group of individuals by their exposure status – exposed vs non-exposed. Group is then followed over time to see who develops the outcome of interest.
Possible to look at multiple outcomes for a given exposure.
Compare rates of disease in groups with different exposures – analytic. Rates can also be calculated for a single group and presented as a descriptive study (with no analysis of exposure).
(slide 38)

Random allocation or randomization is a method which allows chance and only chance to determine the assignment of subjects to the various groups
Randomization
Eliminates selection bias on the part of the participants and investigators
Tends to create groups that are comparable in terms of the distribution of known and more importantly, unknown factors that may influence the outcome (confounders)
(slide 22)

To calculate the crude mortality rate for Cedar Rivers in 2008, we need to determine the total number of deaths and then express it as a rate per 100,000 persons.

Total deaths in Cedar Rivers in 2008 = 1,000 Total population of Cedar Rivers = 100,000

Crude mortality rate = (Total deaths / Total population) * 100,000

Crude mortality rate = (1,000 / 100,000) * 100,000 = 1,000

The specificity of the doctors' clinical judgment refers to the ability of the doctor to correctly identify patients who do not have strep throat. In this case, out of the 112 patients with negative throat cultures, the doctor correctly diagnosed 77 of them as not having strep throat. Therefore, the specificity is calculated as 77/112.

The P-value of 0.4 indicates that there is a 40% chance of obtaining the observed results (similar remission rates) if there was no true difference between the new drug and usual care. This means that the results are not statistically significant, and we cannot conclude that one treatment is better than the other based on this information alone. Other factors such as sample size, study design, and clinical significance should be considered before making a decision about the effectiveness of the treatments.

The sensitivity of clinical diagnosis is calculated by dividing the number of true positive cases (clinically diagnosed cases that were confirmed by autopsy) by the total number of actual positive cases (clinically diagnosed cases). In this case, the number of true positive cases is given as 1,500 and the total number of clinically diagnosed cases is given as 4,000. Therefore, the sensitivity of clinical diagnosis is 1,500/4,000.

The given question is asking about the areas of relative strength and relative weakness of the new test for prostate cancer. The statement mentions that the test yields the same results for every individual repeatedly, indicating high reliability. However, it also mentions that there is a very low correlation between this new test and already-existing tests with proven track records, indicating low validity. Therefore, the relative strength of the new test is reliability, while its relative weakness is validity.

Vehicle: Mode of transport of an infectious agent through the environment to a susceptible host.

Vector: A living carrier – usually an arthropod – that serves as a mode of transport for an infectious agent from an infected host to a susceptible host.

Reservoir: The primary habitat in which an infectious agent survives and reproduces
(slide 7)

The measure of association for each food item is calculated by dividing the number of people who ate the food and developed gastroenteritis by the number of people who ate the food but did not develop gastroenteritis. The measure of association is the highest for Ice Cream, indicating that there is a stronger association between consuming Ice Cream and developing gastroenteritis compared to the other food items.

it is the ODDS of diseas not the INCIDENCE

IF
risk in exposed = p1, and
risk in unexposed = p0
then
risk ratio = p1/p0
IF
odds of disease in exposed = odds1, and odds of disease in unexposed = odds0
Then
odds ratio = odds1/odds0

The predictive value of the doctors' clinical judgment for streptococcal sore throat can be calculated by dividing the number of true positive diagnoses (27) by the sum of true positive diagnoses and false positive diagnoses (27+35). This gives us a fraction of 27/62, indicating that the doctors' clinical judgment correctly diagnosed streptococcal sore throat in 27 out of 62 cases.

true positives/ all positive or 100/100+50 = 2/3 or 67%

2 types of intervention study
Field trials: trials to prevent disease. Involves evaluation of whether an agent or procedure reduces the risk of developing disease among those free from that condition at enrolment. Logistically more difficult to carry out as compared to a clinical trial.
Clinical trials: trials to evaluate one or more new treatments for a disease or condition. Since clinical trials involve diseased persons they are often carried out in hospitals or other clinical settings where those enrolled are treated and followed up for their condition.
(slide 4)