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42 Cards in this Set
- Front
- Back
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Case-control studies:
-Aim & Features -Uses -Outcome measure -Adv -Disadv |
Aim & Features:
-find the associations of a disease (case) with an exposure(s) (outcome measure) -use: test hypotheses, evaluate screening & prevention programs, vaccine & tx efficacy, and outbreak investigation Outcome measure: -Odds Ratio Adv: -short & cheap -efficient for rare disease -efficient disease with long induction/latent period Disadv: -recall bias -control selection -problem matching betw cases and controls -often difficult to establish temporal seq between exposure and disease -inefficient for rare exposures |
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Cohort studies:
-Aim & Features of prospective&retrospective -Uses -Outcome measure -Adv -Disadv |
Aim & Features:
-find the associations of an exposure(s) with a disease/hlth outcome(s) (outcome) PROSPECTIVE -baseline exposure (past and current exposure) is assessed at the start of study -followed over time to compare the incidence of health outcomes RETROSPECTIVE -exposures measured in a defined time in past, then measure outcome up to the present time -thus, BOTH exposures&outcomes have already occured Uses: -test hypotheses, understand physiology, pathogenesis, prognosis, and nat hx of disease, and evaluate screening&prevention programs and vaccine&tx efficacy Adv: -establish temporal seq between exposure and disease (as exposure is assessed at baseline) -can study associations of an exposure with several outcomes -can study multiple exposure -less vulnerable to bias as (i) the outcomes haven't occured when cohort is assembled; and (ii) exposure is assessed at start of study Disadv -expensive -long time (before meaningful data obtained; can be a few d's/wks for infectious disease) -inefficient for rare outcomes -subjects lost to follow-up (>10%) may undermine the study validity -in retrospective study, available data on exposure, outcome, and other key variables may be inadequate |
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Hawthorne effect
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where subjects improves/modifies an aspect of their behavior that is being measured, due to the fact they know they are being studied.
-such changes will decline when study is finished |
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Resentful Demoralization
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Resentment in being placed in the exposure or case group in RCT
-may result in decr motivation & adherence to the allocated tx; or even dropping out of trial |
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Dilution Bias
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Could be a direct conseq of resentful demoralization, where the adherence is not met in some individuals in both exposure and comparison group.
-this results in a dilution of the differences between treatment arms in outcome measures |
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Lack of blinding in RCT can result in...
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-observer/assessm bias
-dilution bias |
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External validity
-def -effect of refusal to participate on external validity |
Extent to which the study results can be generalized to the population
-external validity decr with incr in the no. of ppl who refuse to participate in the trial |
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Internal validity
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Extent to which the confounding factors betw tx grps are minimized
-such that any differences betw grps can be ascribed to the effects of tx. |
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Crossover trial
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-ea. person receives 2 or more diff tx's to be compared
-the order in which tx is given can be randomized Adv: -good for stable long term disease -effect is compared within an individ, thus: ---there is no problem of confounders ---control is not needed -fewer ppl needed for study (statistically efficient, and since no controls needed) Disadv: -order effect (order in which tx is admin'd may affect outcome) -difficult to interpret result : ---if disease/condition changes over time ---carry-over effect - if the effect of one tx persists into the time the other tx is given [can be avoided by long wash-out period] |
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More appropriate term for "normal range" is...
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Reference range/interval
-derived from a large sample of healthy ppl and typically intends to include 95% of the such individuals |
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A reference range based on centiles of the sample measurements allows for variables with...
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allows for variables with skewed distributions (non-Gaussian distribution) that can't be adequately described by the sample mean and SD
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Type I error
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false positive
-when a study detects an effect/association that doesn't exist -nothing to do with sample size |
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Type II error
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false negative
-when a study fails to detect an effect/association that does exist -dependent on sample size, where larger studies are more able to pickup an association |
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Problem with small studies
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-imprecise
-have wide confidence intervals -only the ones with abN'ly large effects that manage to achieve "statistical significance" So, despite we might rely on the "sig" studies, if the only available studies are small, then it is prudent to also consider the "non-sig" studies in estimating the likely size of the effect |
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Types of Studies
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Descriptive
--case series --case reports --cross-sectional Analytical --Experimental -RCT -Crossover trial --Observational: -Case-control -Cohort -Cross-sectional -Ecological |
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Outbreak
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2 or more cases identified from a common source
-i.e. cases w different strains of organisms is NOT an outbreak |
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Types of Outbreak
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Common source:
-all victims acquire disease from the same source (e.g. contaminated water) i) Continuous source: -where exposure occurs continuously over multiple incubation period ii) Point source: -where exposure occurs in less than 1 incubation period Propagated source: -transmission occurs from person-person Zoonotic outbreak -infectious agent is endemic to an animal population (that is transmitted to human) |
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Order of ppl who recognizes an outbreak
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1) Community ppl
2) Media 3) Clinician 4) Local Public Health agencies 5) National Public Health agencies 6) Academic organization |
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Outbreak Investigation
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1) Establish case definition
2) Confirm cases are "real" 3) Establish background rate of disease 4) Find cases, decide if there's outbreak, define scope of outbreak 5) Examine descriptive epidemiologic features of the cases 6) Generate&Test hypotheses 7 Collect&test environmental samples 8) Implement control measures 9) Interact with press, inform public |
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Notifiable diseases
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has potential for outbreak but publich health system can do something about it (control it)
e.g. campylobacter, measles, yellow fever |
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Communicable diseases management
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Eradicate - e.g. small pox (wild; but some kept in lab for research purpose)
Elimination - e.g. polio Control [can't eradicate] e.g. diphtheria, mumps |
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Reproductive Rate (R0)
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R0
= no. of cases over generation / no. of spreaders R0<1 => disease won't spread R0=1 =>endemic R0>1 =>epidemic |
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Herd Immunity
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P (% of pop immunized)
>1-1/R0 Protect only the ones that are spread from person-person i.e. not tetanus |
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Incubation period
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Time between infection till clinical symptom
-usually use middle value rather than interval (median/mean) -distribution of incubation period usually skewed to the L, meaning there are more ppl with short incubation times than long ones --references usually given as the median/mean |
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Latent period
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Time between infection till becoming infectious
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Serial interval
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Time between onset of clinical symptom between 1st patient and 2nd patient
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Vaccine efficacy (VE)
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VE
=(ARU-ARV)/ARU*100% where: ARU = attack rate/incidence unvaccinated ARV ARU = attack rate/incidence vaccinated |
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Process of whether to introduce a vaccine onto the national immunization program
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1) Policy Issues
-public health priority -disease burden -efficacy quality, safety -other inventions (incl. other vaccines, hygiene) -economic & financial issues 2) Programmatic issue -vaccine presentation (what form, valence) -supply availability -programmatic strength Finally, Intro the vaccine/wait for intro |
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Ottawa Charter principles
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1) Create healthy public policy
2) Create supportive environment -"Choice Architecture"=healthy choice is the easier choice 3) Strengthen community action 4) Develop personal skills -NB: education alone doesn't work in health promotion (need policy etc) 5) Reorient health services Public health tends to work upstream at policy/community level |
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Opportunity cost
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-the cost of foregoing a tx option to choose another tx
-next best use of our "scarce" resources (not just $, also time, energy) |
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Prioritization
vs Rationing |
Prioritization
-determine what services the state can provide Rationing -determine who gets access to services and how quickly |
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Explain "Market Failure" in the context of healthcare
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when scarce healthcare is not allocated in the optimal way
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Reasons why Health Market fail
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3 Reasons:
1) Private Health Insurance Markets fail: -expensive premiums due admin costs -moral hazard: ppl change their behavior when insured -adverse selection: insurance market is unable to approp'ly price insurance so healthiest opt out. --BUT if risk is approp'ly priced, then the oldest, sickest and poorest won't be able to afford insurance -hence "Adverse Selection": --when healthier ppl opt out of insurance when they start subsidizing for the unhealthy ppl --Result: only the unhealthy ppl remain in insurance scheme 2) Externalities -health is generally considered as +ve externality (synth/usage has +ve effect so ppl would pay for it) where citizens would be willing to pay for other citizens to receive healthcare -partly "benevolence" - don't like to see others sick/suffer -partly "selfish" - I don't want to be around the sick 3) Info asymmetry between providers and consumers -Dr's know more about how to best convert health care into health status -patient's rely heavily on Dr's advice -free market relies on "perfect info" |
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Quality Adjusted Life Year (QALY)
Ways of measuring QALY |
A method of measuring benefit from tx:
-take each year of life gained from tx and scale it back by the quality of that year -helps to determine the value that individ's place on health states and various attributes of health Ways of measuring: i) Time-trade off: either... a) remain in ill health for a period of time; or b) be restored to perfect health but has a shorter life-expectancy ii) Standard gamble: either... a) remain in ill health for a period of time; or b) undergo an operation which has a chance of either restoring to perfect health or death iii) Visual Analog scale: -rate a state of ill heath on a scale 0-100 (death-perfect health) -NB: adv= easiest to ask; but disadv= most subjective |
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Health states can be measured by...
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-EQ-5D (simplest)
-SF-36 NB: both have been used in NZ -like QALY, helps to determine the value that individ's place on health states and various attributes of health |
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Clinical Priority Assessment Criteria (CPAC)
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A method of prioritizing healthcare:
-pat's assessed using a tool and tally score -despite suff points for elective, if others have higher points, then need to go back to GP for referral again (when one is more ill) |
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NZ: ways of decr'ing waiting list
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i) Reject referral letters (i.e. don't see specialist)
ii) Rejected by specialist following assessment (clinically unwarranted) iii) CPAC (below financial threshold) iv) Ejection from waiting list (booked for elective for 6mo, but fund is unavail) NB: if have money, then some go private |
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NZ Alcohol Foundation:
8 Point Plan for Action on Alcohol |
1) incr "Tax" on alcohol
2) return drinking "Age" to 20 3) strengthen "Sale of Liquor Act" to reduce Teenage Drinking 4) incr "Effective Enforcement" 5) discontinue "Alcohol Ads" 6) allow communities more Control over "Liquor Licensing" 7) incr "Treatment Services" nationwide 8) discontinue "Conscience Voting" on alcohol issues |
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Types of Occupational Hazards
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PCBEP
Physical -En applied to human body Chemical -organic (e.g. solvent has high affinity for fat =>nerve dmg) and inorganic (welding metal) Biological -Hep A (sewage worker) & B (health worker); molds (farmers) Ergonomical -MSK problem; often humans aren't taken into account in equipm design -NB: easier for employer to replace worker than equipm Psychosocial -stress->chronic fatigue, stress-related disorder -NB: not covered by ACC, unless post-traumatic stress disorder |
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Management of Hazard
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IACESIM
Identify Assess Control: -Eliminate --Substitute (if can't eliminate) -Isolate -Minimize |
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In regards to Personal Protective Equipment
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need to be provided and given instruction on how to use
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Health Impact Assessment
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-a process that seeks to inform decision-makers by predicting the health conseq of implementing different options (policy, program, project)
SSARRDIM i) Screening -is it suff health issue that requires HIA? ii) Scoping -path of impact (dir&indir), focus area, types of evid needed 3) Appraisal -gather evid, predict nature/direction/magnitude of impacts 4) Recommendations & Reporting -maximize +ve -minimize/avoid -ve -monitor conseq The following next steps are really the responsibility of the decision-makers, but HIA serves to guide and assist them: 5) Decision-making 6) Implementation & Monitoring |
