MPH 504 - Epidemiology (Module 5 - CBT) - Essay Example

Screening for Diseases 5. If the OD ratio cutoff for tested positive is shifted from A to B the sensitivity will increase to the point where the all HIV infected individuals can be detected. Although the test become more effective in identifying the affected individuals same time it causes high number of false positives rate. This can lead to undesirable psychological, social and health problems when healthy individuals are misdiagnosed as HIV infected.When the OD ratio cutoff for tested positive is shifted from A to C the test become highly specific and nearly all the false positives can be eliminated.

However this also eliminates high number of HIV infected individuals due to reduced sensitivity causing undesirable social and health problems (such as risk of spreading the disease and delay for the treatment). To overcome the problems of both extremes A is the most suitable OD ratio to establish the cutoff.6. Director of Blood Bank: HIV is a deadly disease with no cure. Therefore the intention of screening the donated blood samples against HIV is to totally protect blood receivers from being infected with HIV.

Therefore director of Blood Bank has to set the cut off where he can eliminate almost all the HIV infected blood samples. In other words he has to attain 100% sensitivity. Thereby he has to draw the cutoff line for OD ratio at B eliminating the risk of possible false negatives. However this decision dramatically reduces the specificity by increasing the number of false positives. This leads to rejection of higher number of healthy blood samples.Investigator: The investigator needs to select high risk HIV infected individuals to test the efficacy of his potentially toxic antiviral drug through a clinical trial.

Since the antiviral drug is potentially toxic he has to select only HIV infected individuals without any false positives. Consequently he has to achieve 100% specificity eliminating all false positive. In doing so he should draw the cutoff line for OD ratio at C. However as a result of this decision he has to reject high number of HIV infected individual who tested negative due to low sensitivity resulted from the newly defined cutoff. This makes him recruit a larger sample (than expected) to get the required number of eligible participants.