descriptive studies: person, place and time · descriptive studies: person, place and time....
TRANSCRIPT
Descriptive Studies: pPerson, Place and Time
D i ti E id i lDescriptive Epidemiology• Includes activities related toIncludes activities related to
characterizing the distribution of diseases within a populationdiseases within a population
Analytical EpidemiologyAnalytical Epidemiology• Concerns activities related to
identifying possible causes for the occurrence of diseases
Descriptive Epidemiology
• Epidemiological equivalent of the game “20 Questions”g Q
animal, mineral or vegetable?• In Descriptive Epidemiology:In Descriptive Epidemiology:
Who? - personWhere? placeWhere? - placeWhen? - time
Descriptive Epidemiology
PLACE
TIME
PERSON Think of this as the standard dimensions used to track the occurrence of a disease.
Person
• WHO is getting the disease?• Many variables are involved andMany variables are involved and
studied, but factors such as sex, age & race often have a major effect& race often have a major effect.
Characteristics of PersonCharacteristics of Person• AgeAge• Sex
Ethnic group• Ethnic group• Socioeconomic status• Nativity• Religione g o• Marital status• Occupation• Occupation
Age
Age
Sex
TimeTime• WHEN does the disease occur?WHEN does the disease occur?
“Temporal”Range from hours to decadesRange from hours to decades
• Type of disease dictates “time” element to be usedelement to be used
• Graphic format often usedy-axis (vertical) - frequencyx-axis (horizontal) - time
Characteristics Relating to Time
• Secular change (long-term) • Point epidemics (short-term)Point epidemics (short term) • Cyclic trends
S l i ti• Seasonal variation
Secular Change
Secular Change• Secular changes (“temporal• Secular changes ( temporal
variation”) occur slowly over long periods of timeperiods of time
Longer than one yearIncidence Rates of Cancers in Women
Incidence Rates of Cancers in Men
Point EpidemicsPoint Epidemics• Short-term changes occur over
limited time frameslimited time framesHoursDDaysWeeksMonths
• Used for short-term exposures or diseases with short incubation and/or illness durations
Point EpidemicsPoint Epidemics
Point Epidemicsp
Cyclic TrendsCyclic Trends• Cyclic trends may be either long-y y g
term or short term events.• Some are “seasonal” while othersSome are seasonal while others
are cyclic due to other factors:ImmigrationImmigrationSchool year Military deploymentMilitary deployment
Cyclic TrendsCyclic Trends
Seasonal Variation
• Seasonal i tivariation can
be seen for disome diseases
or conditions f lli ithifalling within a calendar year
Seasonal Variation• Seasonal variation can be used to
suggest possible etiologysuggest possible etiology.
Migratory Birds?
Time Clustering• Time clustering data can sometimes
be used to trace the “beginning” tobe used to trace the “beginning” to the introduction of a specific causal agentagent
Thalidomide & birth defectsFi t k t d i E i 1950’First marketed in Europe in 1950’s as sleeping pill and to treat morning sickness in pregnant women
Toxic Shock SyndromeStaphylococcus aureus infection in women using newly introduced hyperabsorbent tampons
Time Clustering
Place
• WHERE are the rates higher? lower?• Geographic location of sourceGeographic location of source• Geographic location of reservoir
John Snow and Cholera
5 Criteria of Place• ↑ Rate observed in all ethnic groups
in the areain the area• ↑ Rate NOT observed in persons of
similar groups inhabiting other areassimilar groups inhabiting other areas• Healthy persons entering area get ill
at same frequency• People who leave do NOT show
similar levels• Similar levels of infestation in otherSimilar levels of infestation in other
species (if zoonotic disease)
Characteristics Relating to Place
• International • Variation within countriesVariation within countries
Urban-ruralLocalLocal
• Building Maps
PlaceDistribution of AIDS in the US 1990
Local
Building Maps
Interactions ofInteractions of Time and Place
• Time-place clusteringMi ti• Migration