Epidemiology Flashcards by Scott Brenner

Incidence

The number of NEW cases of a disease occurring during a specified period of time.

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Prevalence

Number of individuals with a given disease (current cases) divided by the total number of individuals in the defined population. (proportion of the population with the disease). Given as a percentage or # cases/100,000.

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Point Prevalence

Proportion of individuals within a define population with a given disease at a SINGLE point in time. (Jan 1, 2018)

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Period Prevalence

Proportion of individuals within a defined population who have a given disease within a specified period of time. (example, annual prevalence rate).

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Lifetime prevalence

Proportion of individuals in a defined population who have, have had, or will have a given disease at any time in their lives.

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Incidence rate:

Number of new cases of a disease occurring during a specified period of time DIVIDED by the defined population at the start of that time interval.

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If period prevalence rate is higher than incidence rate, what does that mean? Lower?

Disease lasts longer than the specified period. Chronic disease. If lower, the disease on average lasts shorter than the specified period.

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Experimental Studies

Involve trials that expse at least some study subjects to a factor or agent and assess its role in the PREVENTION or TREATMENT of a particular disease.

Different from observational studies which are natural such that subjects sorted themselves into groups.

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Observational studies

These are the ones used in epidemiology. ‘Natural experiments.’ Look at exposures in NATURAL SETTINGS that can lead to disease states .

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Cohort Study

Epidemiological study in which a group of healthy people are studied that share a common characteristic. ‘What will happen to me? “ study.

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Which study do you use to study the association between exposure to risk factors and disease development?

Cohort Prospective Study. It minimizes the weaknesses of retrospective studies which rely on recall.

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Case-Control Study

Retrospective study in which subjects with a disease or condition are compared against controls , who are people that are as similar as possible to the cases with the single difference being that the control does not have the disease.

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Benefits of Case-Control

Fast: identify 2 groups and compare their past exposures.

Cheap
good for rare diseases
initial study that can lead to prospective (better) or experimental studies.

Weakness: confounding variables can be present.

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What is a confound?

Variable that is not equally distributed among case and control groups. Confounds weaken the ability to interpret study results.

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Cross-sectional study

“Am I Like My Neighbors” Study. Simultaneously examines current exposures and health status in a group or groups.
- Has an assumption that current expsorues have been present for a long time and have had time to effect health outcomes.

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What did the Epidemiological Catchment Area (ECA) Study tell us ?

Told us about the prevalence rate of psychiatric disorders in 1980, DSM III. 5 site study.

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What to know about the National Comorbidity Survey (NCS)?

Estimated prevalence of DSM-III-R, US sample of 10,000 individuals from 1990-1992.

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What to know about the National Comorbidity Survey 2?

10 years later after the NCS, the NCS subjects were resurveyed.

NCS-R Study: what did it tell us?

Same National Comorbdity Survey ‘Replication’ of 10,000 additional new individuals.

Lifetime prevalence of mental illness is high at 46%. 12 month prevalence is 26%.
Mental illness starts early with 50% of all cases with onset by age 14 and 75% by age 24.
Delay to treatment is 6-8 years for mood disorders.

Where are the tails on

positively skewed distribution
negatively skewed distribution

Positive: on the right
Negative: on the left

Correlation coefficient

Can be -1, 0, or 1. 0 Means lack of correlation, 1 is positive, - 1 is negative correlation

Power

The probability of detectinga treatment effect when the treatment effect truly exists.

Parametric vs Non paramentric: Which has more power? Which is more robust?

1) Parametric has more power (normal distribution population)
2) Nonparamentric (non-normal distribution) is more robust.

P value significance

If the p value is lower than the alpha value (expectation that results happen due to chance), a study is deemed to be statistically significant.

Type I error vs Type II error

Type I is false positive, type II is false negative.

When do you use regression?

When you have multiple variables present

Reliability of a test refers to its ability to

Yield similar results when administered by different raters at different times. reliability is repeatability.

Validity of a test refers to its ability to

measure what it intends to measure

Face validity

The extent to which experts who evaluate a test believe that it assesses the condition that it purports to assess.

Content validity

The extent to which a test assesses all the aspects of the condition that it purports to assess.

Construct validity

The extent to which a test shows the relationship with a theoretical construct (if a test is based on a wacky theory of the etiology of depression, then it has a low construct validity) .

Convergent validity

the extent to which a test correlates or coverges ith other tests for the same condition. .

Predictive validity

the extent to which a test is able to predict a future outcome. If a certain type of measurement of hippocampal volume on MRi correlates with the dgree of neurocognitive impairment 5 years hence, your test has a high predictive validity.

Name the concept: What proportion of the people WITH the disease are you CORRECTLY identifying as having the disease?

Sensitivity, "disease present in denominator"

Name the concept: What proportion of people wihout the disease are you correctly identifying as NOT having it?

Specificity, 'disease absent' in the denominator

Positive Predictive value

What proportion of the people with a positive result have the disease?

Negative predictive value?

what proportion of the people with a negative result do NOT have the disease?

What is a Time Series Design?

Study design in which a single group of individuals is studied periodicaly before and after and intervention. There is NO placebo group which differentiates it from randomized controlled study.

What is the Hawthorne effect?

When someone being studied starts behaving atypically due to the fact that they know they are being studied.

Drug trial Phase I

New drug or treatment is tested in a small group of people for the first time to - evaluate safety - determine a safe dosage range - identify side effects

Drug Trial Phase II

The drug or treatment is given to a larger group of people to assess its effectiveness and further evaluate its safety.

Drug Drial Phase III

Drug or t is given to LARGE groups of people to confirm its effectiveness, monitor side effects, compare it to current tx, and collect data to allow the drug or tx to be used safety. NEEDED FOR FDA APPROVAL.

Drug Trial Phase IV

STudies are done after the drug has been FDA approved and marketed. Data is gathered on the durg's effect in vairous pops and side effects associated with long term use and large number of people.

Intent-to-treat analysis is good in what situation?

It is a method of analysis for randomized trials in which all subjects randomly assigned to one of the treatments are analyzed together, regardless of whether or not they completed or received that treatment. Good to combat Attrition Bias, when people drop out of the study. The patients' LAST RATING is used and carried forward.