epi511 set 1

Study of distribution and determinants of health and disease in POPULATIONS

prevent disease from occuring

early detection to change natural history

reducing disability after treatment

Infectious agents
Carcinogens, chemicals
Behaviors, habits, lifestyle
Occupational exposures
aging
genetic constitution
social/political factors

Host
Environment
Agent

Who
Where
When
How
Changes

Higher than normal levels of disease

Ecologic and observation or retrospective cohort design

1. agent recovered from all diseased individuals
2. Agent grows in culture
3. Cultured organism causes new disease in susceptible
4. Agent recovered from new diseased animal

1.Temporal relationship
2.Strength of association (relative rate)
3. Biologic plausibility
4. Risk factor
5. Consistency: association is replicated by other investigators
6. Dose response

1. Resistance to the spread of infectious disease in a group because susceptible members are few, making transmission from an infected member unlikely.
2. The immunologic status of a population, determined by the ratio of resistant to susceptible members and their distribution.

1. define numerator (cases)
a. case definition
2. define denominator: population at risk
3. Calculate attack rate (incidence rate of people at risk)

# at risk with disease/total # at risk

(%)

# contacts who develope disease/
#total susceptible contacts

this also is a measure of tendency of spread in a population

Attack rate % for sick students who ate fish /Attack rate % for sick students who did not eat fish.

A good rule of thumb for determining a relationship for attack rate ratios (or risk ratios) in foodborne disease:
>5 Very strong association (increased risk)
3.0 -<5.0 Strong association (increased risk)
1.7 -<3.0 Moderate association (increased risk)
1.3-1.6 Weak association (increased risk)
0.9-1.2 Probably no association
0.5-0.8 Weak association (decreased risk)

Interval from recipt of infection to the time of onset of clinical illness

the probability to get disease (NEVER 0)

the probabilty to get disease IS ZERO

1. Define disease
2. Define population
3. Find all cases in the population (existing and new)
4. Create measures of case frequency per population

# the total number of cases of a given disease in a specified population at a specified time and/or
# the ratio of the number of cases of a disease present in a statistical population at a specified time and the number of individuals in the population at that specified time.

NOT a measure of risk and NOT a rate

How many on a certain date? aka cross-sectional sample

disease cases present during a specific time interval (NOT a good measure)

bias due to longer disease survivability

proportions, ratios, risk and instataneous rates over TIME

includes the numerator in the denominator

numerator and denominator come from different groups (male/female)

result of rates that prevail over a period of time. Time is not a dimension; only used descriptively to specify a period of observation

number of new cases divided by the candidate population over a period of time.
also be calculated by the incidence rate multiplied by duration.
CI(t)=1-e^{-IR(t) * D}
new cases/initial population at risk

new cases/at risk time

"stroke incidence for males is 5 cases/100,000 person-years

new cases/person-years

total number of something per 1000 people. summary for a population of comparison age group. Not used for inter-population comparisons.

total number of deaths per 1000 people of a given age (e.g. 16-65 or 65+).

Factors affecting a country's death rate

* Nutrition levels
* Standards of diet and housing
* Access to clean drinking water
* Hygiene levels
* Levels of infectious diseases

ALWAYS can be compared between groups.

1. choose a standard population
2. multiply specific rates from pop#1 by standard pop age groups
3. sum the pop#1 and divide by total standard pop, then repeat for #2.
ADJUSTS FOR CONFOUNDING EFFECT

observed deaths in population A/expected deaths based on the proportion in the population B.
Used when actual population numbers are not known. NOTE: NOT rates or risks

#live births in a year/average midyear population x 1000

#deaths in a year/ave mid-year pop x 1000

#deaths in certain age in a year/ave pop in age group x 100

#deaths from cause/mid-year pop x 1000