EPIDEMIOLOGICAL STUDIES; ANALYSIS OF CANCER RISK Flashcards
(36 cards)
2 CATEGORIES OF EPIDEMIOLOGICAL STUDIES
EXPERIMENTAL (AIMAL EXPERIMENTS RCTs..)
OBSERVATIONAL ( COHORT, CASE CONTROL, CROSS SECTIONAL, GENE ENVIRONMENT, GENE-WIDE ASSOCIATION STUDY
OTHER NAMES FOR COHORT STUDY
- LONGITUDINAL STUDY
- INCIDENCE STUDY
- FORWARD LOOKING STUDY
FEATURES OF COHORT STUDIES
- COHORTS ARE IDENTIFIED PRIOR TO APPEREANCE OF DISEASE UNDER INVESTIGATION (E.G. A GROUP THAT HAS A CERTAIN RISK FACTOR)
- THE STUDY GROUPS ARE OBSERVED OVER A PERIOD OF TIME TO DETERMINE THE FREQUENCY OF DISEASE AMONG THEM
- THE STUDY PROCEEDS FROM CAUSE TO EFFECTS
INDICATIONS FOR DOING A COHORT STUDY
- THERE IS GOOD EVIDENCE OF ASSOCIATION BETWEEN EXPOSURE AND DISEASE
- EXPOSURE IS RARE
- ATTRITION OF STUDY POPULATION CAN BE MINIMIZED
- SUFFICIENT FUNDING IS AVAILABLE
TYPES OF COHORT STUDIES
- PROSPECTIVE (CLASSIC EXAMPLE, FOLLOW UP OF EXPOSED VS UNEXPOSED GROUPS TO MONITOR DISEASE DEVELOPMENT)
- RETROSPECTIVE (OUTCOME HAS OCCURED BEFORE THE START OF THE INVESTIGATION, LOOKING BACK AT RECORDS, AKA HISTORICAL COHORT AND NONCURRENT COHORT)
- AMBI-DIRECTIONAL (HAVE ELEMENTS OF BOTH PROSPECTIVE AND RETROSPECTIVE COHORT; THE COHORT IS IDENTIFIES FROM PAST RECORDS AND FOLLOWED UP PROSPECTIVELY INTO THE FUTURE FOR THE FURTHER ASSESSMENT OF OUTCOME)
DISADVANTAGES OF COHORT STUDIES
- MIGHT TAKE A LONG TIME
- REQUIRE A SUFFICIENT AMOUNT OF FUNDING FOR A LONG PERIOD
- MISSING OF STUDY SUBJECTS
- NOT SUITABLE FOR RARE DISEASES
- LARGE POPULATION NEEDED
- STUDY ITSELF MIGHT ALTER PEOPLE’S BEHAVIOURS
- EXTENSIVE RECORD KEEPING
- PROBLEM OF ATTRITION OF INITIAL COHORT IS COMMON
OUTPUTS OF COHORT STUDIES
RELATIVE RISK (INCIDENCE RISK AMONG EXPOSED/INCIDENCE RISK AMONG UNEXPOSED) --> ESTIMATES THE MAGNITUDE OF ASSOCIATION BETWEEN AN EXPOSURE AND DISEASE incidence risk = number of people who develop a condition/ total number of exposed people (or unexposed)
ATTRIBUTABLE RISK (INCIDENCE RISK AMONG AN EXPOSED GROUP - INCIDENCE RISK AMONG A NON-EXPOSED GROUP)
BIASES IN COHORT STUDIES
- DIFFERENTIAL LOSS OF FOLLOW UP
- CONTAMINATION
- SELECTION BIAS
- INFORMATION BIAS
- MISCLASSIFICATION BIAS
OTHER NAMES FOR CASE CONTROL STUDIES
- CASE COMPARISON STUDY
- CASE COMPEER STUDY
- CASE HISTORY STUDY
- CASE REFERENT STUDY
FEATURES OF CASE CONTROL STUDIES
- BOTH EXPOSURE AND OUTCOME HAVE OCCURED BEFORE THE START OF THE STUDY
- THE STUDY PROCEEDS BACKWARDS FROM THE EFFECT TO CAUSE
- IT USES A CONTROL OR COMPARISON GROUP TO SUPPORT OR REFUTE AN INFERENCE
CASE CONTROL VS COHORT STUDIES
CASE CONTROL STARTS WITH DISEASES AND NOT DISEASES, WHILE COHORT STARTS WITH EXPOSED AND UNEXPOSED
CASE CONTROL DETERMINES IF 2 GROUPS DIFFER IN EXPOSURES WHILE IN COHORT STUDIES FOLLOW UP IS DONE TO DETERMINE DIFFERENCE IN RATES AT WHICH DISEASE DEVELOPS IN RELATION TO EXPOSURE
DIFFERENT OUTPUTS
HOW ARE CONTROLS IN CASE CONTROL STUDIES SELECTED?
- COMPARABILITY MORE IMPORTANT THAN REPRESENTATIVENESS
- THE CONTROL SHOULD BE AT RISK OF THE DISEASE
- THE CONTROL SHOULD RESEMBLE THE CASE IN ALL RESPECTES EXCEPT FOR THE PRESENCE OF THE DISEASE
SOURCES OF CASES AND CONTROLS FOR CASE CONTROL STUDIES
HOSPITAL BASED (EASIY RECRUITMENT AND COOPERATION BUT POPULATION WITH MORE RISK FACTORS FOR DISEASES, DOESN’T RESEMBLE GEN POP)
POPULATION BASED (MOST REPRESENTATIVE OF GEN POP!!!!!!!!!!!!, USUALLY HEALTHY, REQUIRES MORE TIME, MONEY AND ENERGY, EXPOSURES TO RISK FACTORS MIGHT BE VERY DIFFERENT)
NEIGHBOURHOOD CONTROLS/TELEPHONE EXCHANG RANDOM DIALLIG (CONTROL AND CASES SIMILAR IN RESIDENCE, EASIER THAN SAMPLING THE POPULATION, BUT LACK OF CO-OPERATION, SECURITY ISSUES, NOT REPRESENTATIV OF GEN POP)
BEST FRIEND CONTROL/SIBLING CONTROL (ACCESSIBLE, COOPERATIVE, OFTEN SIMILAR TO CASES, BUT COULD LEAD TO OVERMATCHING)
BIASES IN CASE CONTROL STUDIES
- SELECTION BIAS
- INFORMATION BIAS
- CONFOUNDING BIAS
OUTPUT OF CASE CONTROL STUDIES
ODDS RATIO (RATIO OF THE ODDS THAT THE CASES WERE EXPOSED TO THE ODDS THAT THE CONTROLS WERE EXPOSED) Odds: the ratio of the number of ways an event can occur to the number of ways an event cannot occur
ADVANTAGES OF CASE CONTROL STUDIES
- ONLY REALISTIC STUDY DESIGN FOR UNCOVERING AETIOLOGY IN RARE DISEASES
- IMPORTANT IN UNDERSTANDING NEW DISEASES
- COMMONLY USED IN OUTBREAKS INVESTIGATION
- USEFUL IF INDUCING PERIOD IS LONG
- RELATIVELY INEXPENSIVE
DISADVANTAGES OF CASE CONTROL STUDIES
- SUSCEPTIBLE TO BIAS IF NOT CAREFULLY DESIGNED
- ESPECIALLY SUSCEPTIBLE TO EXPOSURE MISCLASSIFICATION
- ESPECIALLY SUSCEPTIBLE TO RECALL BIAS
- RESTRICTED TO SINGLE OUTCOME
- INCIDENCE RATES NOT USUALLY CALCULATED
- CANNOT ASSESS EFFECTS OF MATCHING VARIABLES
OTHER NAME FOR CROSS SECTIONAL STUDIES
PREVALENCE STUDIES
WHAT ARE CROSS SECTIONAL STUDIES?
- SINGLE EXAMINATION OF POPULATION (WHOLE OR A SAMPLE) AT ONE POINT IN TIME
- MEASURE EXPOSURE AND EFFECT SIMULTANEOUSLY
TYPES OF CROSS SECTIONAL STUDIES
- POINT PREVALENCE OR PERIOD PREVALENCE
- DESCRIPTIVE (DESCRIBE PRESENCE OF DISEASE, DISABILITY AND SYMPTOMS, DIMENSIONS OF POSITIVE HEALTH, ATTRIBUTES RELATED TO HEALTH) OR ANALYTICAL CROSS-SECTIONAL (STRENGTH OF ASSOCIATION BETWEEN DISEASE AND RISK FACTORS, DETERMINNTS OF DISEASE/CONDITIONS, PREDICTORS OF DISEASE)
ADVANTAGES OF CROSS SECTIONAL STUDIES
- PROVIDE ESTIMATE OF THE DISEASE BURDEN (PREVALENCE)
- RELATIVELY SHORT DURATIO
- EASY AND QUICK
- LESS COSTLY
- USEFUL FOR CHRONIC CONDITIONS WITH LOW CASE FATALITY
- STARTING POINT FOR COHORT STUDIES FOR SCREENING EXISTING DISEASS
- PROVIDE WEALTH OF DATA FOR FURTHER RESEARCH
- ALLOW A RISK STATEMENT, ALTHOUGH THESE ARE NOT PRECISE
DISADVANTAGES OF CROSS SECTIONAL STUDIES
- DOESN’T PROVIDE ESTIMATE OF DISEASE OCCURENCE
- NO DIRECT ESTIMATE OF RISK POSSIBLE
- RARE DISEASES, SHORT DURATION, HIGH FATALITY NOT DETECTED
- NATURAL HISTORY OF DISEASE INFO IS MINMAL
- PRONE FOR BIASES FROM SELECTIVE SURVIVAL
- NOT POSSIBLE TO ESTABLISH TEMPORALITY
- WEAK DESIGN FOR PROVING CAUSALITY
3 MAJOR TYPES OF OBSERVATIONAL STUDIES
- COHORT
- CASE CONTROL
- CROSS SECTIONAL
WHAT IS THE GENE-ENVIRONMENT INTERACTION STUDY?
THE DIFFERENTIAL OF THE GENOTYPE RESPONSE IN CONNECTION WITH THE ENIRONMENTAL VARIATION
