Epidemiology Flashcards
What are the two main groups diseases?
Infectious diseases : illness due to specific infectious agent that arises through transmission form and animal/reservoir to a susceptible host.
Complex disorders: are not transmissible, genetics might be important.
What is the epidemiological triad?
Schematic representation of infectious diseases, we have different factor that play a role in the disease behavior. Environment, age, vector and host.
What are the different phases/periods in an infection?
Latent period: time interval from infection to infectious.
Infectious period: time during which the host can infect another host.
Incubation period: time from infection to development of symptoms.
Symptomatic period: symptoms are present
What is the attack rate?
AR is the number at people at risk who develop disease divided the number of people at risk during a specific period of time. It is useful to compare the risk of disease in groups with different exposures.
What is the basic reproductive number R?
It is a measure of the potential for transmission, it is given by the multiplication of probability of transmission per contact, contact per units of time and duration of the infectious ness.
What is a screening test?
It is a procedure which enable to predict the absence or presence of a disease from knowledge of test results. It uses a bio marker as a sort of indirect measure. If a predefined threshold is broken you have the disease.
What are sensibility and specificity?
Sensibility is the proportion of people with the disease who will have a positive result. In other words ability to confirm disease.It is given by TP/TP+FN.
Specificity refers to the probability of a negative test, conditioned on truly being negative. In other words the ability to identify a disease absence. It is given by TN/TN+FP
What are PPV and NPV?
The positive and negative predictive values (PPV and NPV respectively) are the proportions of positive and negative results in statistics and diagnostic tests that are true positive and true negative results, respectively.
PPV= TP/TP+FP
NPV=TN/TN+FN
What is a bias?
It is also called a differential error and causes distortion in one direction.
What is a random error?
It is also called a non-differential error as it does not cause the deviation in one direction, but it reduces the statistical power and decreases the probability of finding an association.
What are cohort studies?
It is a type of design that follows groups of people over time. There are two types. Prospective type is related to the future and scientist plan to study in advance collecting data over time. Retrospective type is related to the past and scientist already use data that is available.
What is ROC analysis and what is is used for?
It is a curve showing the performance of a model at all classification thresholds. It has been used increasingly in radiology and is used to better analyze data. It better allows for a non dichotomous analysis, giving a better overview of the relationship between specificity and sensibility.
What is the area under the curve?
It is a measure for the diagnostic accuracy of a test.
What is the difference between risk and odds?
The risk is the number of people who experience the event divided the total number of people at risk of having that event. In contrast the odds of an event is the number of those who experience it divided by the number of those who do not. Ex. Odds of 0.2 of an event happening means that 1 event happens for every 5 non events which is a 1/6 which gives 17%.
What are the disadvantages of prospective and retrospective cohort studies?
Prospective : long follow up period while waiting for an event to happen.
Retrospective : limited control over data collection, existing data may be incomplete or inconsistently measured.
