Lecture 13 Research and Study Design and Eval 1

• Possible reasons for changes in trends


  -acute reality -artifactual: errors in NUMERATOR due to: changes in the recognition of disease, changes in the rules and procedures for classification of causes of death, and changes in the accuracy of reporting age at death-errors in DENOMINATOR: due to over- or under estimation of the population at risk
• Clustering is often used to describe:

  aggregation of uncommon conditions such as leukemia
• Descriptive epidemiology: classifies the occurrence of disease according to the following variables: person, place, time
• Define descriptive epidemiological study:

  is one that is concerned with characterizing the amount and distribution of health and disease within a population.
• A descriptive epidemiological study provides valuable information for the following activities


  -prevention of disease-design of interventions-conduct of additional research
• Uses of descriptive epidemiologic studies


  -permit evaluation of trends in health and disease-provide a basis for planning, provision, and evaluation of health services-identify problems to be studied by analytic methods and suggest areas that may be fruitful for further investigation
• What are some types of descriptive epidemiologic studies


  -case reports-case series-cross-sectional studies
• Define case reports


  accounts of a single occurrence of a noteworthy health-related incident or of a small collection of such events-example: rabies in bison (epidemic and zoonotic)
• Define case series

  • is a larger collection of cases of disease, often grouped consecutively and listing common featurescharacteristics of affected patients

  -Example: characteristics of affected patients
• Case reports and series advantages


  -can aggregate cases from disparate sources to generate hypotheses and describe new syndromes-simple to write, simple to read, contains lots of information
• Case reports and series limitations


  -cannot test for statistical association because there is no relevant comparison group-based on individual exposure-cannot establish causality!
• Cross sectional studies


  a type of investigation that examines the relationship between diseases and other variables of interest as they exist in a defined population at one particular time
• An example of a cross sectional study


  a type of prevalence survey or study
• Descriptive epidemiology and descriptive studies provide what?

  a basis for generating hypothesis
• Descriptive epidemiologic studies connect what?


  intimately with the process of epidemiologic inference
• Person variable examples


  -age-sec-race/ethnicity-SES-marital status-nativity-migration-religion
• Define age:


  perhaps the most important factor to consider when describing the occurrence of disease or illness
• Age specific disease rates usually show


  greater variation than rates defined by almost any other personal attribute
• Examples of Age Associations


  -the incidence of and mortality from chronic disease increase with age-some infections occur more commonly during childhood-the leading cause of death among young adults is unintentional injuries
• Define sex:


  epidemiologic studies have shown sex differences in a wide scope of health phenomena including morbidity and mortality
• Socioeconomic status (SES)


  defined as a descriptive term for a persons position in society
• Socioeconomic status (SES) examples:


  -the social class gradient-the higher you are the less badness that happens to you
• Example place variables:


  -international-national-urban-rural differences-localized patterns of disease
• Define international:


  WHO studies: both infectious and chronic diseases show great variation from one country to another
• Define national (Within-country):


  Regional differences may affect the prevalence and incidence of disease
• What are the factors of national:

  -climate-latitude-environmental pollution
• Time variable examples:


  -secular trends-cyclic (seasonal) trends-point epidemics-clustering
• Define secular trends


  refer to gradual changes in the frequency of disease over long time periods
• Secular trend examples


  -yearly suicide rates of US females (firearm associated suicides decreased, but those by hanging increase)-age-adjusted prevalence of hypertension
• Define cyclic (seasonal) trends


  are increases and decreases in the frequency of a disease or other phenomenon over a period of several years or within a year
• Examples of cyclic trends


  -severe weather events in the atlantic basin-mortality from pneumonia and influenza
• Define clustering


  -a closely grouped series of events or cases of a disease or other health-related phenomena with well-defined distribution patterns in relation to time or place or both
• Clustering may reflect


  -common exposure to an etiologic agent-chance occurrences
• Define spatial clustering


  refers to aggregation of events in a geographic region
• Define temporal clustering


  denotes the occurrence of events related to time
• Define endemic


  the habitual presence (or usual occurrence) of a disease within a given geographic area
• Define epidemic


  the occurrence of an infectious disease clearly in excess of normal expectancy, and generated from a common or propagated source
• Define pandemic


  a worldwide epidemic affecting an exceptionally high proportion of the global population
• Sources of Error/Bias in Descriptive Epi examples:


  -chance-selection bias-observation bias
• Define chance


  the role of randomness