Epidemiology

Question 1

• What is a cohort study

Answer 1

• A type of observational study used to help find the association between cause and effect. You observe what happens to groups of people over time and there is NO intervention.

Question 2

• What are advantages and disadvantages of cohort studies?

Answer 2

• Advantages:
  
  • 1) Can get a temporal sequence between exposure and outcome as all individuals must be free of disease at beginning of study.
  • 2) Good for looking at effects of rare exposures.
  • 3) Allows for examination of multiple effects of a single exposure.
  • 4) Not open to bias as much as other types of study
• Disadvantages:
  
  • 1) Tend to be very time consuming and expensive
  • 2) Over long time, may get loss to f/u. This can ‘dilute’ results or lead to bias.
  • 3) Not good for looking at rare diseases.
  • 4) Validity can be seriously affected by loss to f/u if study goes over long time.

Question 3

What is relative risk?

Answer 3

RR=

(incidence of the outcome (disease) in the exposed group)/incidence of the outcome (disease) in the unexposed group

i.e. RR=

_I _exposed/_I_unexposed

• _{good for telling individual risk of developing a disease if exposed to a particular risk factor, but tells us nothing about risk in the general populaion}

Question 4

What is Attributable Risk?

Answer 4

AR=

incidence of the outcome (disease) in the exposed group minus incidence of the outcome (disease) in the unexposed group.

i.e. AR=

I_exposed - I_unexposed

Can be used to calculate NNTT

Question 5

What is NNTT?

Answer 5

The number of people needed to be treated with a drug or who would have to cease an exposure to prevent one case of disease or death (or in the case of drugs in order to reach a designated clinical endpoint)

Question 6

What is the Preventive Fraction?

Answer 6

PF =

(Incidence_unexposed minus Incidence_exposed)divided by Incidence_unexposed

It is often expressed as a percentage and gives an indication of the proportion of disease (or whatever) in the unexposed group that is due to lack of preventative measures or that could be prevented by the beneficial exposure.

Question 7

What is a case control study?

Answer 7

A group of people with a disease are compared to a group of people without the disease from the same population. (i.e. patients are selected on the basis of their disease or outcome status.) Exposure to risk factors in both groups is compared.

Question 8

What are the advantages and disadvantages of case control studies?

Answer 8

Advantages:

1) allows for rapid study of a disease with a long latency period
2) cost and time efficient
3) Good for looking at rare diseases
4) allows for evaluation of a wide range of possible causative factors that might relate to disease being studied.

Disadvantages:

1) very susceptible to bias (esp selection and recall bias) as both disease and exposure had already occurred when participants enter the study.
2) Temporal relationship between exposure and outcome may not be clear.

Question 9

What is the Odds Ratio?

Answer 9

OR=

Odds of exposure in cases (diseased)

Odds of exposure in controls (healthy)

Question 10

What is a Randomised Controlled Trial?

Answer 10

Groups are exposed at random to an intervention and its effect on the outcome of a disease is measured. Ethical considerations limit its applicability.

Question 11

What are the advantages and disadvantages of an RCT?

Answer 11

Advantages: provides powerful evidence of the effect of an intervention and represents the ‘gold standard’ of epidemiological research.

Disadvantages:

1) very limited use due to ethical concerns;
2) comparatively expensive;
3) difficult to design and conduct

Question 12

Key issues to consider in design of RCT

Answer 12

Ethical issues Study population Sample size Sample collection Confounding and randomization Bias, blinding and placebo effect Compliance Outcome measures Stopping rules

Question 13

What is Bias

Answer 13

Bias is any systematic error in an epidemiological study that results in an incorrect estimate of the association between exposure and risk of the outcome.

Question 14

Types of Bias

Answer 14

• Selection Bias -Observation bias including
  1) recall bias;
  2) interviewer bias;
  3) loss to follow-up (cohort studies);
  4) misclassification

Question 15

What is a Confounding Factor?

Answer 15

CF is one that is associated with the expsure and that independently affects the risk of developing the outcome, but that is not an intermediate link in the causal chain between the exposure and the outcome under study.

Question 16

Stillbirth Rate

Answer 16

# of children born dead per year occurring after 24 weeks gestation x 100

number of live & still births in the year

Question 17

What is the Early Neonatal Death Rate

Answer 17

# of deaths per year occurring in the the first week of life x 1000

total number of live births in the year

Question 18

What is the Late Neonatal Death Rate?

Answer 18

# of deaths per year occurring in the the from 1 to 4 weeks of life x 1000

total number of live births in the year

Question 19

What is the Neonatal Death Rate?

Answer 19

The Sum of early and neonatal death rates, i.e.:

# of deaths occuring from birth up to 4 weeks of life x 1000

total number of live births in a year

Question 20

Perinatal Death Rate

Answer 20

Number of still births and early neonatal deaths per year x 1000

Total number of still births and live births per year

Question 21

Post-neonatal Death Rate

Answer 21

# of deaths occurring after 4 weeks of age up to 1 year

total # of livebirths in the year

Question 22

Infant Death Rate

Answer 22

Number of deaths occurring after 4 weeks up to 1 yr x 1000

total number of live births in the year

Question 23

Epidemiology: What is the Morbidity Rate?

Answer 23

Type: Incidence

new cases of disease

total population at risk for this disease

Question 24

• Epidemiology: What is the Mortality Rate?

Answer 24

Type: Incidence

# of deaths from the disease in question or all causes

Total population

Question 25

• Epidemiology: What is the case fatality rate?

Answer 25

Type: Incidence

number of deaths from a specific disease

the number of cases of the disease

Question 26

Epidemiology: What is the Incidence of a disease?

Answer 26

(# of cases of a specific disease)/

(total population at risk, for a limited time of observation)

Question 27

Disease rate at autopsy

Answer 27

Type: prevalence

# of cases of a specific disease

of people autopsied

Question 28

What is the Birth Defect Rate?

Answer 28

Number of babies born with a specific abnormality

Number of live births

Question 29

Period Prevalence

Answer 29

Prevalence

Number of cases plus # of new cases during a given period

Total population

Question 30

Compare and contrast Incidence & Prevalence

Answer 30

Question 31

What is the EBM Hierarchy of Evidence?

Answer 31

In 1995, Guyatt and Sackett published the first such hierarchy.[3]

Greenhalgh put the different types of primary study in the following order:[2]

1. Systematic reviews and meta-analyses of “RCTs with definitive results”.
2. RCTs with definitive results (confidence intervals that do not overlap the threshold clinically significant effect)
3. RCTs with non-definitive results (a point estimate that suggests a clinically significant effect but with confidence intervals overlapping the threshold for this effect)
4. Cohort studies
5. Case-control studies
6. Cross sectional surveys
7. Case reports

Question 32

What is the Incidence Density?

Answer 32

Incidence Density =

# new cases population over spec time

Total person-time at risk

(person-time calculated by multiplying each person by the time included in the study)

This allows for studying population that includes people participating in population for different periods of time

Question 33

What is Prevalence?

Answer 33

Prevalence =

number of cases at a given time or for a given period

number in population at that time

(point prevalence vs period prevalence)

Question 34

What is Cumulative Incidence (CI)

Answer 34

Cumulative Incidence (CI)=

number of new cases arising in a population over specified time

total number at risk per same period of time

Question 35

What is Population Attributable Risk (PAR)?

Answer 35

• estimates excess rate of disease in total population (i.e. exposed + non-exposed) that is attributable to exposure

PAR =

Incidence _{(total pop)} - Incidence _(exposed)

Alternatively, estimated by multiplying attributable risk by exposed portion of population.

Question 36

What is Preventive Fraction (PF)?

Answer 36

If exposure is protective (e.g. vaccine) then:

PF =

Incidence _(unexposed) - Incidence_(exposed)

Incidence _(unexposed)

_{This gives a proportion, not a rate.}

Question 37

What is the Odds Ration (OR)?

Answer 37

OR =

Odds of exposure in the cases (diseased)

Odds of exposure in the controls (healthy)

Odds ratio expressed as a number. It is not a rate. Only good for comparing the odds of a particular exposure existing in a case vs a control.

Question 38

What is Bias?

Answer 38

Bias is any systematic error in an epidemiological study tat results in an incorrect estimate of the association between exposure and the risk of the outcome.

Question 39

Name 4 types of Bias

Answer 39

Selection Bias

Observation Bias

Recall Bias

Loss to Follow up Bias (Cohort Studies)

Question 40

What is a Confounding Factor?

Answer 40

A Confounding Factor is one that is associated with the exposure and that independently affects the risk of developing the outcome, but that is not an intermediate link in the causal chain between the exposure and the outcome under study.

Question 41

How do you control for confounding factors?

Answer 41

1. In Case Control Studies, by matching for possible confounders. (Overmatching may weaken the power of the study if the exposure matched for is associated with the exposure under study.)
2. In analysis stage you can use Stratified Analysis but this will lessen the sample size in each stratum so bigger overall sample is needed.
3. Multivariate analysis allows for production of a mathematical model to describe the association between exposures and outcome.

Question 42

What are the Bradford Hill criteria for causation?

Answer 42

1. Strength of the association
2. Biological credibility
3. Consistency with other investigations
4. Time sequence: cause must precede effect
5. Dose-related response
6. Evidence from animal studies

Question 43

What is the IMR?

Answer 43

Infant Mortality Rate is the number of infant deaths for every 1000 live births.

Question 44

What is a Total Fertility Rate?

Answer 44

The average number of children born to a woman over her lifetime.

TFR estimates the number of children a hypothetical cohort of 1000 females in a specified population would be if:

1) They all went through their childbearing years experiencing the same age-specific birth rates for a specified time period and;
2) They survived to the end of the period.

Question 45

What is e₀?

Answer 45

Life expectancy at birth.

Question 46

What is the Crude Birth Rate?

Answer 46

CBR= total number of births per 1000 people per year

Question 47

What is the Crude Death Rate?

Answer 47

CDR=Total number of deaths per 1000 people per year.

Question 48

Name several kinds of Bias in Critical Appraisal

Answer 48

• Selection bias
  
  • Biased allocation to comparison groups
• Performance bias
  
  • Unequal provision of care apart from treatment under evaluation
• Detection bias
  
  • Biased assessment of outcome
• Attrition bias
  
  • Biased occurrence and handling of deviations from protocol and loss to follow up
• Selective reporting
  
  • you can’t just report as statistically significant unexpected findings that were not addressed by your study design
• Confirmation Bias & Belief Disconfirmation Bias
• Qualitative research: not wrong, just, well qualitative and should be identified as such
• lead time bias

Question 49

What is Critical Appraisal

Answer 49

• Critical appraisal is the process of carefully and systematically examining research to judge its trustworthiness, and its value and relevance in a particular context.

Question 50

How are Absolute Risk Reduction (AR) and Number Needed to Treat (NNT) related?

i.e. NNT=?

Answer 50

NNT=1/ARR

Question 51

What is Absolute Risk (AR) and how is it calculated?

Answer 51

• Absolute risk reduction, also termed risk difference, is the difference between the absolute risk of an event in the intervention group and the absolute risk in the control group.
• The absolute risk reduction can be calculated by subtracting the proportion of patients in the treatment group from that in the control group.

Question 52

What is the Relative Risk?

Answer 52

• Relative risk, also known as risk ratio, is the risk of an event in the experimental group divided by that in the control group.

Question 53

• What is the Odds Ratio and how is it calculated?
• Discuss it’s significance.

Answer 53

• An odds ratio (OR) is a measure of association between an exposure and an outcome. The OR represents the odds that an outcome will occur given a particular exposure, compared to the odds of the outcome occurring in the absence of that exposure.
• Odds can also be expressed as the risk (or probability) of an event occurring over the risk of an event not occurring.
• The odds ratio is gradually losing favour as a measure of treatment effect, particularly as data from which relative risk is derived can also be used to calculate absolute risk reduction and number needed to treat, which are more clinically useful.

Question 55

• Sampling Methods: HIV Epidemic States
  
  • Define 3 levels

Answer 55

• HIV Epidemic States
  
  • Low Level
    
    • Confined to persons with high risk behavior
    • HIV prevalence not above 5% in any sub population
  • Concentrated
    
    • HIV prevalence above 5% in one or more at risk populations
    • HIV prevalence not above 1% in pregnant women in urban areas
  • Generalised
    
    • Well established in general population
    • HIV prevalence consistently above 1% in pregnant women in urban areas

Question 56

• Sampling Methods: Define Target Population and Study Population

Answer 56

• Target Population
  
  • The population where we want to make an inference.
• Study Population
  
  • The population from which the sample is drawn.

Question 57

• Sampling methods:
  
  • Define
    
    • Sampling Unit
    • Sampling Frame

Answer 57

• Sampling Unit
  
  • The individual elements in the population to select frame.
• Sampling Frame
  
  • A list of all the elements (units) in the study population.

Question 58

What is Volunteer Bias?

Answer 58

• The term volunteer bias refers to a specific bias that can occur when the subjects who volunteer to participate in a research project are different in some ways from the general population.
• If this occurs, the researcher has sampled only a subset of the population, and consequently, the data gathered are not representative of all people, merely of those that choose to volunteer.
• Volunteer bias is a challenge to the external validity of any research project.

Question 59

• Sampling Methods
  
  • What is homophily?

Answer 59

• Homophily from Ancient Greek ὁμοῦ (homou, “together”) and Greek φιλία (philia, “friendship”) is the tendency of individuals to associate and bond with similar others, as in the proverb “birds of a feather flock together”.
• Leads to selection bias similar to Volunteer Bias
• Homophilic Selection Bias

Question 60

What is Respondent Driven Sampling?

Answer 60

• Respondent Driven Sampling combines ‘Snowball sampling’ with a mathematical model that weighs the sample to compensate for the fact that the sample was collected in a non-random way.
• A non-traditional non-probability sampling method used for sampling ‘hidden populations’ in which it is impossible to acquire a complete sampling frame.
• Attempts to control bias associated with chain-referral methods through
  
  • long referral chains, which reach “equilibrium” after 4-6 waves
  • final sample
    
    • independent of those initially non-randomly selected as seeds
    • similar to population of network from which you are recruiting
      *

Question 61

What is R₀ and what is its significance?

Answer 61

• R₀ is the Basic Reproduction Rate
• It is used to measure the transmission potential of a disease.
• the number of secondary infections produced by a typical case of an infection in a population that is totally susceptible.
• If R₀ is >1, a disease will continue to spread
• Goal for eradication is to get R₀ < 1

Question 62

Distinguish Efficacy from Effectiveness.

List 7 aspects of study design relevant to ensuring that a trial is about Effectiveness rather than just efficacy.

Answer 62

• Efficacy trials (explanatory trials) determine whether an intervention produces the expected result under ideal circumstances. Effectiveness trials (pragmatic trials) measure the degree of beneficial effect under “real world” clinical settings. Hence, hypotheses and study designs of an effectiveness trial are formulated based on conditions of routine clinical practice and on outcomes essential for clinical decisions.
  1. Populations in primary care
  2. Less stringent eligibility criteria
  3. Health outcomes
  4. Long study duration; clinically relevant treatment modalities
  5. Assessment of adverse events
  6. Adequate sample size to assess a minimally important difference from a patient perspective
  7. Intention-to-treat analysis

Question 63

• What are the criteria for priority setting?

Answer 63

• Health priorities and health services priorities
  
  • Demand approach
    
    • Prioritize the top 3 or 5 according to morbidity and mortality in the district
    • remote rural areas may not be quantified
  • Needs approach
    
    • distinguish between felt or perceived needs and normative (or professionally prescribed needs).
• Priority public health actions
  
  • based on economic appraisals to measure burden of disease: “technical elements of PHC” or World Bank “basic health packages”
• Priority Groups
  
  • needing special attention, may be geographically, demographically or ethnically defined
• Combined priority matrix
  
  • in order to apply demand and needs approach at local level
  • List of health problems ranked in group exercise according to 4 criteria:
    
    1. Frequency
    2. Severity
    3. People’s concern
    4. Sensitivity to public health: “can something useful be done”.
  • Prioritization of Health Services’ Problems according to
    
    1. Negative impact on population’s health
    2. How far from expected results
    3. Is it considered a problem by community
    4. Possibility of improvement at district level

Question 64

Efficacy vs Efficiency in Needs Assessment and Planning (NAP)

Answer 64

• Efficacy refers to results achieved by service wrt individual user. The denominator are those who really received the vaccine or drug.
• eg vaccine efficacy = #of children effectively protected/#of children vaccinated
• clinic efficacy = # of pts cured/# of pts treated
• Efficiency shows relationship between costs of resources and results achieved
• eg immunization programme: costs of programme/#of children vaccinated
• TB control: costs of programme/# of pts cured

Question 65

What 5 qualities are GRADED in a Cochrane Review?

Briefly describe each.

Answer 65

1. Risk of Bias
   
   • methods of sequence generation
   • allocation concealment
   • blinding of participants, providers, outcome assessors
   • loss to follow-up
   • failure to follow intention to treat principles in analysis
   • selective outcome reporting
   • other sources of bias such as stopping the trial for benefit, design specific issues relating to non-standard trial design such as cluster or crossover studies
2. Consistency
   
   • Eye Ball test: look at the Forest Plot. Do results look consistent.
   • I² statistic 0-40% suggests low heterogeneity (good)
   • Chi² test approaching 1 suggests differences observed between studies due to chance. i.e. consistent
3. Directness
   
   • how do results apply to review question, i.e. applicability, generalizability, “efficacy vs effectiveness” wrt question under review, clinical utility
   • are these the participants we are interested in? the right intervention? the right comparitor?
4. Precision
   
   • is the study adequately powered?
   • are there enough events (rule of thumb at least 300 for a dichotomous variable; 400 for continuous outcomes)
   • are the results statistically significant
   • are the confidence intervals wide or narrow
5. Publication Bias
   
   • is there a systematic under or over estimation of effects due to selective publication? Is data available for review?
   • look at pattern of results using funnel plot: smaller trial results should scatter more widely and the scatter should be symmetrically distributed

Question 66

What is a Cochrane Review?

Answer 66

• Cochrane Reviews are systematic reviews of primary research in human health care and health policy, and are internationally recognized as the highest standard in evidence-based health care resources. They investigate the effects of interventions for prevention, treatment, and rehabilitation.

Question 67

How does WHO define Essential Medicines?

Answer 67

Question 68

What is Global Health Policy?

(WHO)

What is it for?

Answer 68

• Health policy refers to decisions, plans and actions that are undertaken to achieve specific health goals within a society.
• Defines a vision for the future which in tun helps to establish targets.
• Outlines priorities and the expected roles of different groups.
• Builds consensus and informs people.

Question 69

What is the difference between policy and strategy?

Answer 69

• Policy
  
  • is a guide to thinking and action for those responsible for making decisions.
  • decision oriented
  • introverted approach
• Strategy
  
  • deals with the allocation and deployment of resources to achieve the desired goals within constraints.
  • action oriented
  • extroverted approach

Question 70

Social determinants and health inequalities

What role do they play in Who priorities

Answer 70

• recognized as a fundamental and priority area in the 12 WHO general programme of work 2014-2019
• 3 overarching recommnedationsof Commission on Social Determinants of Health
  
  • to improve living conditions
  • to tackle the inequitable distribution of power, money and resources
  • to measure the problem and assess the impact of action

Question 71

• Epidemiologic transition and importance of NCD’s
• How many deaths in total 2012?
• How many NCD’s?
• How many and what proportion in low and middle-income countries?
• What were top 10 causes of death globally in 2012

Answer 71

• 57 million total deaths
• 38 million (68%) NCDs
  
  • 28 million (3/4) in low and middle income countries

1. Ischemic Ht Disease
2. Stroke
3. Lower Resp Tract Infection
4. COPD
5. Trachea, bronchitis
6. Diebetes
7. Alzheimer
8. Diarrheal Disease
9. TB
10. Road Injury

• (HIV, preterm birthe and road asphyxia have fallen off this list since 2010.)

Question 73

Sustainable Development Goals Relevant to NCD’s

17 Goals 169 targets

Which ones relevant?

Answer 73

• Goal 3 health and well being
• 3.1 by 2030 reduce the global MMR to less than 70/100,000 live births
  
  • (currently rich countries 12/100,000, LIC 239/100,000, global 216/100,000)
• 3.4 by 2030 to reduce by 1/3 prem mortality from NCD’s through prevention & treatment and promote mental health and well-being
• 3.6 by 2020 half the number of global deaths and injuries from MVA’s
• 3a strengthen teh implementation of WHO Framework Convention on Tobacco Control
• 3d strengthen the capacity of all countries, esp dev countries for early warning, risk reduction and management of national and global health risks

Question 74

Describe the three domains of health protection and show each is relevant in LMICs

What are the roles and responsibilities of Health Protection?

Answer 74

• Health Protection
  
  1. Communicable Disease Control
  2. Emergency preparedness resilience (EPPR)
  3. Environmental Public Health
• Roles and Responsibilities
  
  • Planning and preparing for outbreaks or complex situations
  • prevention of disease
  • early detection (surveillance) eg air quality
  • risk assessment
  • investigation and control: contact tracing, quarantine, chemoprophylaxis
  • public health leadership

Question 75

• Define the international health regulations and critique their implementation

Answer 75

• What are they? A set of internationally binding regulations governing the monitoring and reporting of diseases mandated by the WHO wrt core functions of
  
  1. case detection
  2. reporting
  3. investigation and confirmation
  4. analysis
  5. interpretation and action of diseases.
• they also govern a set of support funcions wrt setting standards, traind and supervision, communications and resource management.
• What’s wrong with them?
  
  • nobody can be bothered to implement them them.
  • 42 countries did, 81 asked for an extension, 48 did not respond
• The problem is time, resources and political will to respond to a big bureaucracy.

Question 76

Principles of outbreak management

Answer 76

• confirm the outbreak
  
  • case defninitions and case ascertainment
  • case identification: when? where? tests?
• investigate
  
  • epidemiological
  • microbiological
  • environmental
• Generate and test hypotheses
• Implement control measures
• enhanced surveillance
• Close outbreak
• write report and communicate results

Question 77

DAFI the Duck Checklist for Critical Appraisal of a Study.

What are the questions?

Answer 77

• Description

1. What was the Aim of the study?
2. Who were studied
3. What method or methods were used ?
4. What did they measure (outcomes, dependent variables) or document (views, perspectives or behaviours)
   
   • Appraisal of Methods
5. Is the design appropriate to stated aim/objectives?
6. How were the participants identified and selected?
7. Are the measurements likely to be valid and reliable? Or in studies using qualitative data collection methods, is it clear how data were collected.
8. Are the Analytic Metods adequately described to answer this question.
   
   • F​indings
9. Summarize the Results
10. Summarize the statistical significance (epidemiological studies) or relevance (qualitative studies)
    
    • I​nterpretation
11. In light of your appraisal of the methods, what do the main findings mean?
12. Could the results be the result of bias? Or for qualitative research focus on any attempts to validate or verify the findings.
13. Can the results be generalized
14. What are the implications for policy, practice or research.

Notes:

• a) Are the basic data adequately described?
• b) Do the numbers add up?
• c) Was statistical significance assessed for quantitative studies?

For qualitative studies

• a) Is the type of analysis appropriate for the type of study?
• b) Are quotes used and are these appropriate and sufficent to support the findings?
• c) was reliability of the data analysis and interpretations checked?

Question 78

What is Equity in Health?

Answer 78

• A working definition of equity in health

• “Equity in health implies that ideally everyone should have a fair opportunity to attain their full health potential and, more pragmatically, that no-one should be disadvantaged from achieving this potential, if it can be avoided…Equity is therefore concerned with creating equal opportunities for health and bringing health differentials down to the lowest level possible”

(Whitehead, 2000)

Question 79

What is the difference between gender and sex?

Answer 79

• sex - the biological differences between men and women
• gender - characteristics of women and men that are socially and culturally constructed - women and men’s different behaviour, roles, expectations and responsibilities in a given cultural context.

Question 80

Why might fewer women be diagnosed with TB than men and women take longer to get a diagnosis?

Answer 80

• Sex, not Gender
• question arose because TB notification rates were higher in men than women, with lower case detection rates amongst women than men in “passive screening case finding”.
• Could this be due to gender differences in access to health services.
• However, Borgdorff (2000) showed that prevalence of TB was in fact much lower in women than men, even greater than difference in notification rates.
• subsequently confirmed in other studies.
• Suggestions biological differences make men more susceptible to TB ? larger lungs, higher iron levels mediating hepcidin differences that mediate macrophage resistance

Question 81

Discuss the role of policies at various levels in promoting greater equity in health

Answer 81

• Structural approaches: transforming gender inequalities
• Uphold legislation and policies to protect women (and men) from abuse – e.g. laws on violence against women, marriage age, divorce, inheritance
• Improve economic opportunities for women – e.g. through cash transfer, micro-credit programmes
• Health promotion approaches that enable women and men to reflect on gender norms, stereotypes and power
• Working with men to challenge gender inequalities – e.g. through peer education and mentorship

Question 82

What is the hierarchy of epidemiologic evidence?

Answer 82

• Strenght of evidence with interventional studies eg. RCT at top, qualitative studies (e.g. case study) at bottom
• issue is strength of ability to draw inferences about causation
• more descriptive studies done because easier to do
• RCT>Cohort study>Case Control Study > case study or purely describptive study

Question 83

• What is an ecological study?
• Strengths?
• Weaknesses?

Answer 83

• An ecological study is an observational study defined by the level at which data are analysed, namely at the population or group level, rather than individual level. Ecological studies are often used to measure prevalence and incidence of disease, particularly when disease is rare.
• At least one variable relates to a group or community rather than individual
• Outcome (disease) is compared between groups
• tells you something about the relationship of one variable to another (correlation coefficient r)
• Strengths
  
  • useful as first step in investigation of an association btw exposure or rf and an outcome
  • quick, inexpensive
  • wide range of routine data available
• Weaknesses
  
  • unable to positively link exposure with outcome in part. individuals
  • unable to control for the effect of confounding factors
  • hard to identify non-linear associations

Question 84

What is a cross-sectional study?

Answer 84

• takes a “snapshot’ of a population in time, drawing on existing data
• provide useful data on prevalence of certain conditions or diseases and of certain potential risk factors
• useful for the formulation of hypotheses
• Weaknesses
  
  • unable to discover a temporal relationship between exposure and health outcome

Question 85

Cohort studies

What are they?

Advantages, disadvantages?

Answer 85

• A study design where one or more samples (called cohorts) are followed prospectively and subsequent status evaluations with respect to a disease or outcome are conducted to determine which initial participants exposure characteristics (risk factors) are associated with it.
• no intervention, looking at associations between identified risk factors and outcomes
• Pro
  
  • can get temporal relation between exposure and outcome as all individuals free of the disease at the beginning of the study
  • good for looking at effects of rare exposures
  • allows for exam of multiple effects of a single exposure
  • less open to bias than other types of study
• Cons
  
  • time, money
  • loss to fu over time
  • not good for looking at rare diseases

Question 86

What is a Confounding Factor?

Answer 86

Question 87

What is a Forest Plot?

Answer 87

• A forest plot, also known as a blobbogram, is a graphical display of estimated results from a number of scientific studies addressing the same question, along with the overall results.

Question 89

What is a risk of Bias Table?

Answer 89

• A commonly found form of tool in a critical appraisal is the Risk of Bias Table

Includes assessments of

• Random sequence generation (selection bias)
• Allocation concealment (selection bias)
• Binding of participants and personnel (performance bias)
• Blinding of outcome assessment (detection bias)
• Incomplete outcome data (attrition bias)
• Selective reporting (reporting bias)
• Other bias

Question 90

What is a Prisma Diagram?

Answer 90

• PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) is an evidence-based minimum set of items aimed at helping authors to report a wide array of systematic reviews and meta-analyses that assess the benefits and harms of a health care intervention.
• A PRISMA Flow Diagram, described in the PRISMA Statement is a graphical representation of the flow of citations reviewed in the course of a Systematic Review.