HaDPop Flashcards
What is a census?
The simultaneous recording of demographic data by the government at a particular time pertaining to all the persons who live in a particular territory
What are the features of a census?
Run by government Covers a defined area Personal enumeration Simultaneous throughout defined area Universal coverage Occurs at regular intervals
What is crude birth rate?
Number of live births per 1,000 population
What is general fertility rate?
Number of live births per 1,000 females aged 15-44 years
What is total period fertility rate?
The average number of children that would be born to a hypothetical woman in her life - all of age specific fertility rates together
Removes influence of age group structure
What is fecundity?
Physical ability to reproduce
What is fertility?
Realisation of fecundity potential as births
What is crude death rate?
Number of deaths per 1,000 population
What is age-specific death rate?
Number of deaths per 1,000 in age group
What is SMR?
Standardised mortality ratio
Compares observed number of deaths with expected number if age-sex distributions of populations were identical
Adjusts for age-sex distribution
What is the difference between population estimates and projections?
Estimates - apply what is known about births, deaths and migration to the present
Projections - future orientation of estimates, assumptions made about births, deaths and migration in the future
What is an incidence rate and how is it calculated?
Number of new cases in a time period
IR = new events/person x time (years) = events per persons per year
What is prevalence?
Number of existing cases - this is not a rate
What is the relationship between incidence and prevalence?
P ~ I x L
L = length of disease
Describe systematic variation
Incidence is a measure of the population’s average risk of disease, but in a population not all people have the same ‘proneness’ or ‘risk’ of disease. There are variations in risk of disease between groups of people
How is incidence rate ratio calculated?
Rate B (exposed) / Rate A (unexposed)
What is the difference between rate and ratio?
Rate = absolute risk Ratio = relative risk
What is a p value?
The probability of obtaining a test statistic at least as extreme as the one that was actually observed, assuming that the null hypothesis is true
What does p < 0.05
Data inconsistent with stated hypothesis
What is a 95% confidence interval?
The range that we are 95% sure the true value of the underlying tendency lies
How do you calculate the confidence interval?
Lower 95% CI = observed value / ef
Upper 95% CI = observed value x ef
What are the features of a cohort study?
Recruit disease-free individuals
Classify into exposed and unexposed
For each group, follow-up over time
What are the advantages of a cohort study?
Can study exposures and personal characteristics that are not routinely collected
Obtain more detailed information
Can study a range of outcomes
Study a rare exposure
Establishing that exposure precedes outcome
What is the difference between internal or external comparisons for a cohort study?
Internal - two sub-cohorts studied
External - compared against reference population
What are the limitations of a cohort study?
Large and resource intensive Takes a long time Survivor bias Not good for rare diseases Difficulty with confounding
What are the features of a case-control study?
Identify cases and controls
Ascertain previous exposure status
Compare level of exposure in cases and controls
What calculations would be used in a case-control study?
Odds ratio = ad/bc
How could the precision of an OR be increased?
Increase the number of controls (up to a point of 4-6 times the number of cases)
What is a nested case-control study?
A case-control study nested within a cohort study. It matches controls to those case identified with the disease of interest by certain factors, e.g. age, sex, location
What are the key issues with case-controlled studies?
Selection bias - predominant
Information bias - e.g. Misclassification bias, systematic bias
Confounding - can be reduced by matching
How can you evaluate the strength of evidence in favour of a cause-effect relationship?
Bradford Hill Criteria for Causality: 1. Association features: Strength of association Specificity of association Consistency of association 2. Exposure/outcome Temporal sequence (exposure preceding outcome) Dose response Reversibility 3. Other evidence Coherence of theory Biological plausibility Analogy (that exists with other diseases, species or settings)
Describe the hierarchy of evidence
Systematic reviews (and meta-analysis) Randomised controlled trials Cohort studies Case-control studies Cross-sectional surveys Case reports
What is a clinical trial and what is its purpose?
Any form of a planned experiment which involves patients and is designed to elucidate the most appropriate method of treatment of future patients with a given medical condition
Purpose: to provide reliable evidence of treatment efficacy and safety
What 3 things does a clinical trial need to be?
Fair, controlled and reproducible
What are the problems with RCTs?
Selection bias - by patient, clinicians or investigator
Confounding - known and unknown
What are the problems with a RCT that compares with historical records?
Selection often less well defined
Treated differently
Less information about potential bias/confounders
Unable to control for confounders
Describe the steps involved with RCT
Define: 1. disease 2. treatments to be compared 3. outcomes to be measured 4. bias and confounders 5. patients eligible 6. patients to be excluded Conduct: 1. identify source of patients 2. invite 3. consent 4. allocate 5. follow up 6. minimise losses to follow-up 7. maximise compliance Comparison of outcomes 1. statistically significant (could it have arisen by chance) 2. clinically important (how big is the difference between treatment groups)
Describe the benefits of random allocation in RCT
Minimises allocation bias and confounding
Describe the benefits of blinding
Blinds patient, clinician and investigator to treatment being received. Prevents knowledge of treatment altering outcome e.g. non-treatment effect, measurement bias
What is the placebo effect?
An illness, and the patient’s attitude, may be improved by a feeling that something is being done about it
What is a placebo?
An inert substance used to remove placebo effect in active treatment - there are ethical issues with this
Describe ethical issues surrounding the use of placebos
Should only be used when no standard treatment is available - Declaration of Helsinki 2000
Placebo is a form of deception - therefore patients must be told that they may be receiving a placebo
What are the features of an ideal outcome?
Appropriate and relevant Valid and attributable Sensitive and specific Reliable and robust Simple and sustainable Cheap and timely
What is the difference between explanatory trial and pragmatic trial?
Explanatory trial = as-treated analysis - losses effects of randomisation, gives larger sizes of effect
Pragmatic trial = intention-to-treat analysis - gives smaller more realistic sizes of effects
Describe the difference between collective and individual ethics
Collective ethic - all patients should have treatments that are properly tested for efficacy and safety
Individual ethic:
Principle of beneficence (do good)
Principle of non-maleficence (do no harm)
Principle of autonomy (choice)
Principle of justice
What issues should be considered for a clinical trial to be regarded as ethical?
Clinical equipoise (reasonable uncertainty or genuine ignorance about better treatment or intervention) Scientifically robust (addresses relevant or important issue) Ethical recruitment (inappropriate inclusion and exclusion of certain people) Valid consent (knowledgeable informant, appropriate information (written and verbal), informed participant) Voluntariness (decision free from coercsion or manipulation)
What are the two types of literature review?
Expert review
Systematic review
What are the benefits of a systematic review compared to expert review?
Explicit, transparent, reproducible - unbiased, objective
What is a systematic review?
Overview of primary studies that used explicit and reproducible methods
What is a meta-analysis?
Quantitative synthesis of results of 2 or more primary studies that address the same hypothesis in the same way
What are the advantages of a meta-analysis?
- Facilitate synthesis of large number of study results
- Systematically collate study results
- Decreases problems of interpretation due to variation in sampling
- Quantify effect sizes and their uncertainty as a pooled estimate
What is a pooled estimate?
OR for all studies
What is the null hypothesis value for an odds ratio?
1
What is the null hypothesis value for IRR/SMR?
0
What is heterogeneity?
Ideally all studies included should be similar in terms of:
design; participant profile; treatments/exposures; outcomes measured; statistical analysis used
What are the two approaches to deal with heterogeneity?
Fixed effects model (use if p>0.05) - assumes that studies are estimating exactly the same effect size
Random effects model (use if p<0.05) - assumes that studies are estimating similar, not the same, effect size - accounts for variation
What is publication bias and how is this assessed?
Studies with favourable results are more likely to be published
Funnel plot
