HLTC19: Chronic Diseases (Midterm) Flashcards
what is a population?
a group of people with common characteristic(s)
eg. gender, age, occupation, etc.
focuses on the distribution of health-related states/events in specified populations
descriptive epidemiology
quantifying how often a disease arises in a population
disease frequency
quantifying disease frequency involves:
- developing a definition of disease
- instituting a mechanism for counting cases of disease w/in specified population
- determining size of said population
focuses on determinants of health-related states or events in specified populations
analytic epidemiology
factors that bring about a change in a person’s health or makes a difference in a person’s health
disease determinants
what are some goals and applications of epidemiology in relation to chronic diseases?
- control health problems
- determine extent of disease in a population
- identify patterns and trends in disease occurrence
- identify causes of disease
- evaluate effectiveness of measures that prevent and treat disease
how does the WHO define chronic diseases?
chronic diseases are diseases of long duration with slow progression
what are some common themes in defining chronic disease?
- share common risk factors
- begin slowly and develop gradually over time
- can occur at any age (but more common in adulthood)
- impact quality of life and limit daily activities
- require long-term management with multiple services required
what are the 4 major chronic diseases?
- CVD
- Cancer
- Chronic respiratory diseases
- Diabetes
what is the goal of public health?
to promote the health of the population through organized community efforts
the state of complete physical, mental, and social well-being, not merely the absence of disease
health
the study of pattern and causes of health-related outcomes and application of these findings to the improvement of public health
epidemiology
a set of criteria that must be fulfilled to identify a person as representing a case of a particular disease
case definition
a continuum b/w risk factors and disease as end result of continuum
chronic disease continuum
overarching factors that are largely outside the control of the individual that have significant trickle down effects on other, more proximal determinants of public health
upstream determinants
type of population where membership is defined at a point in time or an event, is permanent, and does not change
close/fixed population
eg. Japanese atomic bomb survivors
type of population where membership is defined on the basis of a changeable state or condition and is transient
open/dynamic population
eg. cancer registry (people added as they are diagnosed)
the shift from infectious and deficiency diseases to chronic, non-communicable diseases
epidemiological transition
rate of occurrence of new cases of disease in a population at risk during a specified period of time
incidence
frequency of current cases of disease (old + new) in a population at risk during a specified period of time
prevalence
(proportion/rate)
_____ tell us what fraction of the population is affected; _____ tell us how fast the disease is occurring
PROPORTIONS tell us what fraction of the population is affected; RATES tell us how fast the disease is occurring
- # of new health-related events in a defined population within a specified period of time
- measures risk
incidence
the fraction of people who experience the onset of the event during a specified time period
cumulative incidence / incidence proportion
(used when people are followed the entire time!!!)
vs. incidence rate when people are followed for a certain period of time/until disease occurs
what is the formula for cumulative incidence?
the rate at which new events occur in a population; takes into account variable time periods at risk
incidence density / incidence rate
total amount of time <strong>EACH </strong>person was observed
what is the formula for incidence density / incidence rate?
- the proportion of individuals in a population who have a disease or condition
- measures burden of an event
prevalence
what is the formula for prevalence?
percentage of people in a population with the condition at a specific point in time
point prevalence
percentage of people in a population with the condition over a specified period of time
period prevalence
what are some factors that impact prevalence?
- as incidence increases, prevalence _____
- as # of people cured increases, prevalence _____
- as # of people that survive increases, prevalence _____
- as more people die from disease, prevalence _____
- as incidence increases, prevalence increases
- as # of people cured increases, prevalence decreases
- as # of people that survive increases, prevalence increases
- as more people die from disease, prevalence decreases
an event/condition/characteristic that preceded disease onset and that, had the event/condition/characteristic been different, the disease would not have occurred at all or would not have occurred until some time later
cause
measures public health impact of an exposure (difference in measures)
absolute measure of comparison
measures strength of relationship of 2 factors (ratio of measures)
relative measure of comparison
difference in rate of occurrence of disease due to exposure
risk/rate difference
what is the formula for risk/rate difference?
RD = riskexposed - riskunexposed
what does risk difference (RD) = 0 mean?
- risk in exposed = risk in unexposed
- no increased risk attributed to exposure
what does risk difference (RD) > 0 mean?
- risk in exposed is greater than risk in non-exposed
- excess risk attributed to exposure
what does risk difference (RD) < 0 mean?
- risk in exposed is less than risk in exposed
- decreased risk attributed to exposure (“protective*)
risk of disease in exposed compared to risk of disease in unexposed
risk/rate ratio (RR)
aka as relative risk
what is the formula for risk/rate ratio (relative risk)?
RR = Rexposed / Runexposed
what does it mean when relative risk (RR) = 1?
- risk in exposed is the same as risk in unexposed
- there is no association b/w disease and exposure
what does it mean when relative risk (RR) > 1?
- risk in exposed is greater than risk in unexposed
- there is a positive association b/w 2 factors
what does it mean when relative risk (RR) < 1?
- risk in exposed is lesser than risk in unexposed
- there is a negative association b/w 2 factors
what are the advantages and disadvantages of using an absolute measurement (ie. risk difference)?
advantages:
- public health impact
- absolute change measured
disadvantage:
- less commonly used
what are the advantages and disadvantages of using a relative measurement (ie. relative risk)?
advantages:
- can measure strength of association
- commonly used
disadvantage:
- hard to interpret
what is the 2-step process epidemiologists use when approaching causation?
- assessing whether observation is valid or true
- causal inference
what are the essential attributes of true causes?
association: cause (X) must occur together with effect (Y)
time order: cause must precede the effect (time periods can be short or long)
directionality: asymmetrical relationship b/w cause and effect (want X to cause Y but don’t want Y to cause X)
focuses on the origins of the web of causation, including social, political, and economic determinants of health instead of individual-level determinants
ecosocial framework
a complete causal mechanism that inevitably causes disease
sufficient cause
each participating factor in a sufficient cause
component cause
a causal component that it is a member of every sufficient cause
necessary cause
what are the key attributes of a sufficient-component cause model?
- blocking action of one component stops completion of sufficient cause (just need to know one to prevent disease)
- completion of sufficient cause leads to biological onset of disease
- component causes may act far apart in time
level of prevention that aims to prevent disease from occurring and reduce incidence
primary prevention
level of prevention that delays onset and duration of clinical disease and aims to improve survival
secondary prevention
level of prevention that slow disease progression and aims to improve survival
tertiary prevention
why is a clear research question important?
formulating research questions precisely enables you to design a study with a good chance of answering them
what is the PICO framework for research questions?
Population: sample of participants in study
Intervention: treatment provided to participants
Comparison: reference group used to compare with intervention
Outcome: measure used to examine treatment effectiveness
what is the PECO framework for research questions?
P: population of interest
E: exposure level of participants
C: reference group used to compare with exposure
O: measure used to examine effects of exposure
aims to collect valid and precise info about causes, prevention, and treatment of disease (to determine relationship b/w exposure and disease)
analytic epidemiological research
experimental vs. observational studies: PICO or PECO?
- experimental studies follow PICO framework
- observational studies follow PECO framework/PO (population outcome)
what are the different directions for observational studies?
cohort study: when looking at exposure BEFORE outcome
case-control study: when looking at exposure AFTER outcome (look at outcome first then exposure)
cross-sectional study: when exposure and outcome are looked at at the same time
when the investigator actively manipulates which groups receive the agent under study
experimental studies
ensures that known and unknown potential confounders are equally distributed among groups and that they have similar baseline characteristics
randomization
what are some advantages of RCTs?
- prospective
- randomization
- clear temporal sequence
- strong evidence for causation
what are some disadvantages of RCTs?
- contrived situation; might not reflect real world consequences
- ethical restraints
- human behaviour may be difficult to control
- exclusions may limit generalizability
- expensive to conduct
when the investigator passively observes as nature takes its course
observational studies
makes causal inferences about the association b/w exposure and disease
observational studies
examines the relationship b/w exposure status and disease status at the same time for each subject
cross-sectional studies
what are some advantages of cross-sectional studies?
- inexpensive
- quick to conduct
what are some disadvantages of cross-sectional studies?
- may exclude those with disease who died before study began
- cannot establish temporality of relationship
type of study that examines multiple health effects of an exposure
cohort studies
when subjects are defined according to their exposure levels and followed for disease occurrence over time
cohort studies
any designated group of persons who are followed or traced over a period of time
cohort
a study where the cohort is assembled at present time and followed toward future (study initiated before outcomes occur)
prospective cohort study
a study where the cohort is assembled in the past using existing records and is “followed” to present time (study initiated after outcomes occur)
retrospective/historical cohort study
a combination of a prospective and retrospective cohort study
ambidirectional cohort study
what are some similarities b/w cohort studies and RCTs?
- both can compare 2 or more exposure groups
- both follow subjects to monitor outcomes
- both can monitor more than one outcome
- select groups for comparability
what are the major differences in an RCT vs. a cohort study?
- researcher allocates exposure
- randomization of exposure status to groups
- can use placebo and masking/blinding
- interval b/w action of exposure and disease onset
- time required for a specific cause to produce an outcome
induction period
eg. how long does it take for smoking to cause lung cancer?
- interval b/w disease onset and clinical diagnosis
- the time b/w the disease’s first presence and its recognition
latent period
eg. how long after someone develops lung cancer do they start showing clinical symptoms?
what are some advantages of cohort studies?
- temporality established (exposure precedes outcome)
- establishes incidence of disease
- quality control measures can be implemented (prospective)
- inexpensive and fast to conduct (retrospective)
what are some disadvantages of cohort studies?
- expensive when outcome is rare or follow-up is long (prospective)
- maintaining participation is difficult/loss to follow-up (prospective)
- quality of data poor; rely only on available info (retrospective)
where data is originally collected
data source
when original data is collected for a specific purpose by or for an investigator
prospective data
existing data that was recorded for another purpose
retrospective data (secondary use)
captures demographic info on all individuals who received a HC # in Ontario (updates addresses)
Registered Persons Database (RPDB)
arises from a systematic difference in the way that the exposure or outcome is measured b/w compared groups; results in different accuracy of info b/w comparison groups
information bias
systematic differences b/w study groups in terms of accuracy or completeness of recall of past events
recall bias
systematic difference in soliciting, recording, or interpreting info involving interviewers
interviewer/observer bias
probability that test correctly classifies positive individuals who have pre-clinical disease
sensitivity
probability that test correctly classifies individuals w/o pre-clinical disease as negative
specificity
proportion of individuals with a positive test who have preclinical disease
positive predictor value (PPV)
(↑ prevalence= ↑ PPV)
proportion of individuals w/o preclinical disease who test negative
negative predictor value (NPV)
(↑ prevalence= ↓ NPV)
when a test has an extremely high Specificity, a Positive results tends to rule in the diagnosis
SpPin
when a test has an extremely high Sensitivity, a Negative result rules out the diagnosis
SnNout
how to address information bias?
- comprehensive questions to improve recall and self-reporting (eg. close-ended questions)
- standardized questionnaires, mask interviewer (if possible)
- self-administered questions
- validate data with another source
- consistency b/w repeated measurement
- repeatability or reproducibility of a test (get the same results everytime)
reliability
the degree to which a variable represents what its intended to represent
validity
- the degree to which study results are true for people being studied
- validity of comparisons made w/in the study
internal validity
- probability that observed result is due to chance
- directly related to sample size
- variability in data that can’t be explained by the design or still remains after systematic error is eliminated
random error
occurs when there is a systematic difference b/w individuals included in the study and individuals not included in the study (during selection and follow-up of participants)
selection bias
- mixing of effects b/w exposure, outcome, and a 3rd variable (another exposure)
- effects of the 2 exposure cannot be separated
confounding
bias can affect the _____ of a study
bias can affect the INTERNAL VALIDITY of a study
errors that results from procedures used to select subjects and from factors that influence participation in the study
selection bias
- comes from selecting study subjects from a larger population
- extent to which results are generalizable/applicable to another study population
external validity (generalizability)
what are the major sources of information bias?
- recall bias
- interviewer/observer bias
what are the 3 key characteristics of confounders?
- must be associated with exposure
- must be a risk factor for the outcome
- must not be an intermediate step in the causal pathways b/w exposure and disease
how can we control for confounding?
at the design stage:
- randomization
- restriction
- matching
at the analysis stage:
- standardization
- stratification
- matched analysis (for case-control studies)
- multivariate analysis
when subjects with identical (or near identical) characteristics are selected across compared groups
matching
separating study population into homogenous categories of a confounder
stratification
eg. everyone’s a smoker in the smoker stratum
mathematical model that can control for multiple confounders simultaneously
multivariate analysis
