• age
• sex
• race/ethnicity

• geographic location
• proximity to exposure
• clustering

3 aspects of "Place" of the epidemiologic triad

1. Increased in amount of virulence
2. Recent intro of agent into a new setting
3. Enhanced mode of transmission
4. Factors that increase host exposure or involve introduction through new portals

1. a case may be a source
2. some people may be immune
3. there's sometimes a need for urgency
4. preventative measures have a clear scientific basis

• A ratio where the numerator is included in the denominator
• Tells us what fraction of the population is affected
• Ex. males/total population

• a defined time interval
• # of events occurring in that time interval
• population at risk in that time interval
• a multiplier or constant (x10, X100, etc)

# of new events during a given time period/

population at risk during this time period

x100

• Cumulative incidence calculated for a specific disease for a limited time period during an epidemic
• Usually in relation to food-borne ilnesses
• measured from beginning of outbreak to end of outbreak

# of existing events, old and new/population at risk 

x1000

• measures the frequency of all existing events at a given instant of time
• ex: existing cases on 9/16/1979

• measures frequency of existing cases for a prescribed period of time
• ex: existing cases in 1975

• probability statement during given period of time
• ex: 1 in a million chance of developing cancer in 70 years

# of new cases of disease during period

/

total "person time" of observation

• early detection leads to more favorable prognosis
• pre cinical-disease left untreated progresses to clinically evident disease
• disease should be serious
• prevalence of pre-clinical disease should be relatively high among those screened

1. financial
2. anxiety
3. some morbidity occurs
4. creation of lead time morbidity (lead-time- the time by which screening advances diagnosis)

Sensitivity

The following are three key features of what type of studies?

Extraneous variable

example:  drinking coffee causes CVD

an extraneous variable could involve smoking

What can influence the dependent variable that researchers are unaware of in an experimental study? 

• Cues in an experiment that may lead a participant to respond in a particular fashion

Main efficacy variable being studied

ex: lower BP, better controlled DM, absence of sx

Additional variables thought to be important

ex: quality of life, return of normal function, patient satisfaction

What phase of clinical trial involves

• Researchers test an experimental drug or tx on a small group of people (10-30)
• first time to be evaluated
• determines safety, safe dosage and range, and identifies side effects

What phase of clinical trials involve

• experimental study drug or tx given to a larger number of people (100-300)
• sees if it is effective and further evaluates it's safety

What phase of clinical trials involves

• experimental drug or tx given to a large group of people (1,000 - 3,000)
• confirms effectiveness, monitors side effects, compares it to commonly used tx, and collects info that will allow the experimental drug or tx to be used safely

What phase of clinical trials involves

• Post- marketing studies to delineate additional information including the drug risks, benefits, and optimal use

• Participants receive real treatment or placebo and then are switched to opposite treatment
• This trial doubles the number of people in the trial

• Clinical trial
• the investigaor determines who gets the exposure and who does not

• Studies that make an attempt to describe patterns of disease and antecedent factors as they occur in "free-range" human population
• Often provide first clues as to the relationship between exposure and outcomes
• Ex: fluoride and dental care, or smoking and lung CA

• Type of descriptive study that provide population wide estimates of disease rates vs exposure
• Data often compares countries across the world
• Ex; dietary fat intake by countries and breast cancer

• Case reports
• Cross-sectional
• Ecological

1. Cohort Studies (prospective and retrospective)
2. Case-Control studies

• In this type of cohort study, exposure and outcome have already occurred
• Subjects have a disease

• In this type of cohort study, outcome has yet to occur
• Subjects are disease free

The following are advantages of what type of cohort study:

• cost (follow up is not required)
• Time (uses data from records)
• rare outcomes (studies rare outcomes by going through records)

• What type of analytic study begins with the outcome and proceed to look back at the hx of exposure

odds for exposure among cases/odds for exposure among controls

       a/c

OR= ______

       b/d

What are 3 ways you select controls for case-control studies?  And if all three ways are not met what will you have?

1. General population
2. Random digit dialing
3. Neighborhood
4. Friends/Relatives
5. Hospital/clinic-based

optimal 1:1

should not exceed 1:4

What is the optimal case-control ratio?

What should the ratio not exceed?

1. Self report
2. Records
3. Interviews with surrogates (spouses, children)

A hybrid design in which a case-control study is within a cohort study

cases------COHORT STUDY----controls

• quick and inexpensive
• well suited for evaluation of disease with long induction periods
• optimal for evaluation of rare diseases
• can examine multiple etiologic factors for a single disease

• inefficient for evaluation of rare exposures
• difficult to establish the temporal relationship between exposure and disease
• prone to bias

• Disease free individuals are selected and their exposure status is ascertained
• Subjects are followed for a period of time to record and compare the incidence of disease between exposed and non-exposed (Risk ratio)

• This is the strongest observational study
• Examines multiple effects/outcomes
• Yields info on multiple exposures
• Allows direct measurement of incidence of disease in exposed and non-exposed group

• This study is not efficient study for rare diseases
• is costly and time consuming
• requires a large sample size
• changes over time in diagnostic methods can lead to bias

• In this type of study, two groups are selected- one of people with the disease (case) and the other of people without the disease (control)
• Compares past exposure in both groups

Incidence E+ / Incidence E-

          A/A+B

   RR= ________

         C/C+D

• Useful for rare cases
• inexpensive
• quick results

# of deaths of specific disease/# of people who had the disease

x100

annual death count / total population mid point in time

x100 or x1000