M3: Observational Research, Cohort and Case-Control Studies

basic research

-is conducted to increase knowledge and fundamental understanding of the physical, chemical and functional mechanisms of life processes and disease

-is not directed to solving any particular problems in humans or animals

applied research

involves the application of existing knowledge, much of which is obtained through basic research, to solve a practical problem

clinical research

patient or end user-oriented research with human subjects

translational research

part of a unidirectional continuum in which research findings are moved from the researcher’s bench to the patient’s bedsite and to the community

descriptive

-describes an outcome in a population

-a characterizes who, where, or when in relation to the what

analytical

examine the relationship between an intervention/exposure and an outcome in a population

qualitative

-subjective/interpretive observations

-identifies themes in observations

-forms narrative/story/essay

-does not test a hypothesis, but may lead to hypothesis development

quantitative

-objective/measurable data that is typically analyzed statistically

-test a hypothesis

quantitative research designs

-observational

-experimental

-quasi-experimental

observational research

-non-manipulated study

-researchers do not attempt to influence/manipulate participants or the surroundings

experimental research

-manipulated study

-participants are randomized to receive intervention or control

quasi-experimental

one or more aspects/elements of experimental research is absent or missing

utility of observational research

-studying the otherwise unstudy-able

-prioritizing external validity

-generating research questions

cross sectional research

-participants are observed at one point in time

-data/measurements are collected once

-outcomes: single measure, prevalence of disease/events

cross sectional advantages

-attrition is not a concern

-less costs/expenses

-controls for period effects

-data on ALL variables are collected at one time

cross sectional disadvantages

-do not know temporal aspects

-associations identified between variables may be difficult to interpret

-‘snapshot’ timing not guaranteed to be reflective of real-world settings

longitudinal research

-participants are observed over time

-data/measurements are collected multiple times

-outcome: change over time provides indication of incidence of disease

longitudinal advantages

-you may observe a pattern in the outcome over time

-establishes an order of events

-reduces recall bias of participants

-may provide insight into casual bias mechanisms

longitudinal disadvantages

-time consuming and expensive

-usually requires a large sample size

-affected by ‘cohort effects’

-cannot be used to suggest causation, only associations

-despite temporal aspects, may not know if exposure preceeds outcome

prevalence

-the total number of individuals in a population who have a disease of health condition at a specific period of time

incidence

-the number of individuals who develop a specific disease of experience a health-related event during a particular time period

incidence

-the number of individuals who develop a specific disease of experience a health-related event during a particular time period

case control study

participants are recruited based on an outcome of interes

cohort study

-participants are recruited from a population of interest

-longitudinal study

-example: Framingham heart study

cohort

a collection or sampling or individuals who share common experiences and/or characteristics such as sex, age, activity level, location, education, ect.

prospective cohort studies

-participants are recruited and followed forward in time

-outcome is evaluated in the future

retrospective cohort studies

-participants are recruited and they identify past exposures

-outcome is evaluated at time of recruitment

advantages of cohort studies

-longitudinal

-best external validity

-representative

multiple exposure outcomes

disadvantages of cohort studies

-large sample is required

-expensive

-attrition bias

-measurement bias

-poor internal validity

attrition bias

occurs when participants drop out of a long-term experiment or study

measurement bias

a form of inaccurate measurement in which the data consistently overestimate or underestimate the true value of an event

case

those with outcome/disease of interest

control

those without outcome/disease of interest

advantages of case control studies

-smaller # of people needed

-because disease is already prevalent, no need for longitudinal

recruiting for case control studies

-population based

-hospital based

population based recruitment strengths

-cases are representative of population

-results are generalizable to population

population based recruitment weaknesses

more difficult to recruit

hospital based recruitment strengths

-easy to identify

-typically have access to medical history

Hospital based recruitment weaknesses

-may be more sick than general population or population cases

-may be different in other ways compared to general population

control group recruitment

-want to control for potential confounding variables

-often recruit from family or friends

selection bias

occurs when the subjects studied are not representative of the target population about which conclusions are to be drawn

recall bias

type of information bias common in case-control studies where the cases (or their families) are more likely to recall a prior exposure than the controls

non-differential misclassification

-cases and controls are misclassified equally

-will make detection of a true effect less likely

differential misclassificiation

-only one group are misclassified

-can alter the magnitude and/or direction of the effect

case control study design

-cross sectional or longitudinal

-longitudinal are always retrospective

absolute risk

-the actual risk of some event happening given the current exposure

-no comparison between groups

relative risk

odds ratios

-measure of how strongly an even is associated with exposure

-the odds of the even occurring in an exposed group versus the odds of the event occurring in a non-exposed group