Term
| Which are the modes of transmission of an infectious disease? |
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Definition
1. Direct: person to person
2. Indirect: A) Common vehicle (e.g. single exposure, multiple exposure and continuous exposure). B) Vector. |
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Term
| What are the components of the epidemiological triad of disease? |
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Definition
| Host, environment, agent and vector |
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Term
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Definition
| When an individual is carrying an infectious disease but has no clinical or serologic evidence of infection. |
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Term
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Definition
It is the protection provided to susceptible individuals by non-susceptible individuals. This occurs because in this context there is a decreased likelihood of an infectious person to come in contact with a susceptible person. The level of immunity required for herd immunity to occur depends on the infectiousness of the disease. Some conditions for HI to occur are:
1. D mode of transmission is direct.
2. Infection creates good immunity.
3. D limited to single host.
It operates optimally with constant mixing of the population |
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Term
| What is the fundamental assumption of infectious disease dynamic? |
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Definition
| The number of new infections per unit of time is a function of the number susceptible and the number who are infectious |
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Term
| What are the 3 critical elements of an outbreak investigation? |
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Definition
1. When did exposure occur?
2. When did disease began?
3. What is the incubation period?
If you have any 2 elements, the third can be estimated. |
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Term
| What are the 9 criteria for causal association? |
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Definition
1. Temporality
2. Dose response.
3. Biologic plausability
4. If other hypothesis have been considered.
5. Strength of association
6. Compatible with current knowledge
7. Replication of findings
8. Cessation when exposure stopped
9. Gradient response |
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Term
| What epidemiological method and measure of association is used to establish the risk when comparing multiple potential agents? |
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Definition
| Cross-tabulation. The MA that is used is the Attack Rate. |
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Term
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Definition
| How fast an event occurs. It requires time. |
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Term
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Definition
| It is a fraction of people affected by an event. |
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Term
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Definition
| It is a rate that denotes the number of new events that occur in a specific period of time. It is a measure of RISK. It is used for etiology. |
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Term
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Definition
| It is a measure of risk. Number affected/number at risk in a specific period of time. |
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Term
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Definition
| It is the number of events at a point in time. It is not a measure of risk because the numerator has a mix of people with different duration of disease. It is an important measure of burden of disease. |
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Term
| What is point prevalence? |
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Definition
| It is the number of events at a specific point in time |
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Term
| What is period prevalence? |
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Definition
| It is the number of events at any point during a period of time. |
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Term
| What is epidemiological surveillance? |
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Definition
| It is the ongoing systematic collection, analysis and interpretation of health data that is essential for planning, implementation and evaluation of PH practice. This is closely integrated with a system for the timely dissemination of data. |
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Term
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Definition
| It is a measure of risk. # of deaths/# people in pop at midyear. over a period of time. |
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Term
| Prevalence is a function of...? |
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Definition
Incidence X duration of Disease
This is true in a steady state population, when migration in=to migration out. |
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Term
| What is direct age adjustment and what is it used for? |
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Definition
| Direct age adjustment is an epidemiological technique that is used to compare to different populations. Direct adjustment uses the data from the populations and applies it to a standard population, by doing this, the two differing populations are now comparable. This type of adjustment eliminates the effect of age, which is the single most important predictor of mortality. |
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Term
| When is the mortality rate a good indicator of the incidence? |
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Definition
1. When CFR is high.
2. When duration of disease is short. |
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Term
| What is indirect age adjustment? |
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Definition
| It is an epidemiological technique used to compare 2 different population. With indirect Adjustment, we use the data form the population and will apply it to the sub-population. It is used when no age specific information is available for the sub-population. The Standard Mortality Ratio is obtained from dividing the Obs death/expected. |
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Term
| What is the cohort effect? |
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Definition
| It is a phenomena that is observed with mortality data over time. If you analyze cross-sectional data, you might end up with the wrong conclusion regarding the risk of death of a specific disease. It is important when observing mortality trends over time to think if the changes observed are given by the cohort effect. |
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Term
| Age adjusted death rates are used to...? |
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Definition
| Eliminate the effect of differences in age distribution in comparing death rates. |
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Term
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Definition
| It is the ability of a test to distinguish between diseased and non-diseased. |
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Term
| What are some of the characteristics of sequential testing? |
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Definition
1. First test very sensitive.
2. Second test very specific.
By doing this, at the end, you will increase the net specificity (When compared to first test) and decrease the net sensitivity. |
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Term
| What are some of the characteristics of simultaneous testing? |
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Definition
1. You will have increased net sensitivity.
2. Decrease in net specificity (when compared to both test). |
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Term
| What are two factors that affect the predictive value? |
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Definition
1. The prevalence of disease in the population. The higher the prevalence, the higher the PPV.
2. When disease is rare, the specificity of the test being used.
2. |
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Term
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Definition
Can a test be repeated. This will depend of 3 factors:
1. Intrasubject variability (variation observed within individuals).
2. Intraobserver variability (var. of interpretation of results in a single individual).
3. Interobserver variability (variability among observer in interpreting results). |
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Term
| What is the Kappa statistic? |
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Definition
| It is a statistic that shows us the level of agreement between observers that is above of what would be expected by chance alone. It is usually accepted that a Kappa >0.75 represents excellent agreement and below 0.4 is poor agreement. |
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Term
| What are the assumptions made when using a life table? |
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Definition
1. There are no secular (temporal) trends in effectivness of tx or in survivorship over calendar time.
2. Survival experience of those lost to follow up is the same as for those who stayed in the study. |
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Term
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Definition
| It is ideal to evaluate effectivness and side effects of a new intervention. |
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Term
| Who was the first to conduct a RCT? |
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Definition
| Pare in XVI century. It was not planned. Tx at the time for wounds (oil) vs a mixture of eg yolk, roses and turpentine. |
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Term
| When was the first RCT conducted? |
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Definition
| In the XVIII century. James Lind. Scurvy. 50 years after the experiment, the British Navy recommended citrus as part of the daily diet for seamen |
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Term
| What are the advantages of using historical controls and when can they be useful? |
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Definition
| This type of control can be used when a disease has a high mortality rate, and there is no tx for it, so hx control can be compared to px receiving new tx (still, temporal changes need to be rules out). It has to be considered that hx records were not collected for research, so information may be limited for this group. A solution is to use Simultaneous Non-randomized controls. |
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Term
| What are some examples of problems with simultaneous non-randomized controls? |
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Definition
1. Captain and nausea pills.
2. BCG in cooperative vs non-cooperative.
3. Anti coagulant for those admitted to hospital on even number. |
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Term
| Which type of design is the best for a clinical trial? |
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Definition
| Randomization. The critical element of randomization is the unpredictability of the next assignment. |
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Term
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Definition
1.Randomization table.
2. Sealed envelopes |
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Term
| What is stratified randomization and what is it used for? |
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Definition
| Because randomization does not guarantee that groups will be comparable, we can stratify groups based on factors that we know to be relevant (eg smoke, age, etc). By doing this, we are now certain that groups will have equal number of people with relevant factors and will increase the likelihood that groups are comparable. Randomization is made when we have the groups stratified. |
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Term
| What are the two types of cross-over and what are their characteristics? |
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Definition
1. Planned: px assigned to one intervention. After being followed for certain period of time, it is measured and it moves to the other group. A px can be used as his own control. A concern is carryover, this is, that effect from tx A is carried to tx B. Decrease in enthusiasim with time.
2. Unplanned: People who change group that was assigned by randomization. We want to keep this to a minimum. A way to analyze this is doing the primary analysis by intention to treat, where you compare people based on how they were randmomized. |
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Term
| What is a factorial study design? |
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Definition
| Used with 2 different drugs that have 2 different outcomes and act independently. This is done in same group of px a the same time. |
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Term
| What is needed to estimate a sample size in a RCT? |
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Definition
1. Alfa
2. Power
3. Delta: difference in response rates between groups.
4. An estimate of the response rate in one of the groups
4. One sided or two sided test. |
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Term
| What is a ratio of risks? |
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Definition
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Term
| Describe the phases involved in a RCT? |
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Definition
Phase 1: clinical and pharmacologic studies of 50-80 persons. Safety is addressed.
Phase 2: 100-200 persons. efficacy and relative safety.
Phase 3: >1000 persons. Usually multi-center. Safety and effectiveness.
Phase 4:post-marketing surveillance for adverse events. |
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Term
| When doing a RCT, is the external validity increased? |
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Definition
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Term
| What is the major purpose of random assignment in a clinical trial? |
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Definition
| Reduce selection bias in the allocation of treatment. |
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Term
| In many studies examining the association between estrogens and endometrial cancer, a one sided significance test was used. the justification for using a one sided instead of 2 sided test was? |
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Definition
| That researchers expected to find that estrogens were related to endometrial cancer |
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Term
| What is an important reason when choosing a cohort study over a RCT? |
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Definition
| In both designs, we go from exposure to disease. In the RCT, the exposure is usually an intervention that we suppose that is not harmful. When some exposure has been associated with a disease, we can use a cohort study to assess association between them. A very important difference, is that there is no randomization. |
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Term
| What are the types of cohort study? |
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Definition
Prospective: individuals are followed in time.
Retrospective: We use past information, but we would still go from exposure (ascertained from records) to disease. It is less time consuming.
The design for both it's the same. |
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Term
| Mention some of the most common biases observed in cohort studies |
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Definition
1. Bias in assessment of the outcome: when person making dx knows about the exposure status.
2. Information Bias: different info for exposed and non-exposed. More important in retrospective trials.
3. Biases due to non-response and lost to follow-up: if px with disease are lost to follow-up, we migh underestimate the IR.
4. Analytic Bias: from researchers having a preconception about the results. |
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Term
| Why can cohort studies be impractical? |
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Definition
1. Time
2. When doing a retrospective cohort, quality of information might be bad or not existant.
3. Difficulties in assessing exposed and non-exposed.
4. Very expensive |
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Term
| In a cohort study that studies the role of an exposure in the development of a disease, it is essential that: |
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Definition
| Exp and non-Exp groups under study are similar with regard to identified confounding factors. |
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Term
| What are some of the advantages of a prospective cohort design? |
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Definition
1. IR can be estimated.
2. Expo can be assessed.
3. Multiple outcomes can be evaluated.
4. Recall bias is minimized when compared to case control studies. |
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Term
| Name some of the characteristics of retrospective cohort studies |
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Definition
1. Similar sample size as prospective.
2. Not useful for rare exposures.
3. Begin by defining exp and non-expo.
4. IR can be estimated. |
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Term
| What is one of the major problems with non-randomization in cohort studies? |
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Definition
| The possibility that a factor that led to the exposure, rather than the exposure itself is the cause of the disease. |
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Term
| What is one of the mayor advantages of starting a cohort study by selecting the population and not be selecting expo an non-expo? |
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Definition
| That we can study multiple exposures at the same time. |
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Term
| What are some of the limitations of using hospital data? |
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Definition
1. Patients in the hospitals are selected in basis of: severity of disease, comorbidity, personal characteristics, admission policies.
2. Data collected not intended for research.
3. Population at risk difficult to define (denominator) |
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