Key Points Flashcards
Define CBR
crude birth rate: number of live births per 1000 people
Define GFR
general fertility rate: number of live births per 1000 females aged 15-44 years
Define TPFR
total period fertility rate: the average number of children that would be born to a hypothetical women in her life
Define fecundity
The physical ability to reproduce.
Define 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.
Define fertility
The realisation of the ability to reproduce as births.
What is fertility increase by?
increased sexual activity and better economic climate
What is fertility decreased by?
contraception and abortion
What is the use of CBR?
describing the impact of births on the size of the population
What is the use of GFR?
comparing fertility of fertile female populations
What is the use of TPFR?
comparing fertility of fertile female populations without being influenced by age-group structure
Define CDR
crude death rate: number of deaths per 1000 people
Define ASDR
age specific death rate: number of deaths per 1000 people in a specific age group
What is the SMR?
standardised mortality rate: compares observed number of deaths will expected number of deaths if age-sex distribution of the population compared to the reference were identical
Which things affect population size?
births (fertility rates), deaths and migration
Who will be missed off a census?
Homeless people
What is a fairly common problem in hospitals that leads to statistical errors?
classification or coding errors
Define chance
the occurrence of events without any obvious cause
Define bias
the inclination or prejudice for or against something, considered unfair
Define confounder
variable that correlates with both the dependent and independent variables without being on the causal pathway, usually a variable that was not adjusted for
Define incidence
The number of new cases of a disease in a population in a specific time period.
Define prevalence
The number of people with a particular disease in a population at a given time.
What kind of statistic is prevalence?
A proportion
What is the formula for incidence rate?
new events / (people x time (yrs))
Define aetiology
cause (of a disease)
What is the formula for the IRR?
rate B (exposed) / rate A (unexposed)
exposed/unexposed
Rate is a measure of what kind of risk?
Absolute risk
Ratio is a measure of what kind of risk?
Relative
How is SMR expressed?
As a percentage
100 = same risk in both population >100 = higher risk in study population than reference
What is the null hypothesis if it is a rate and if it is a difference?
rate = 1 difference = 0
Define hypothesis
a statement that an underlying tendency of scientific interest takes a particular quantitative value
What does it mean if p
we can reject Ho because the probability of getting an observation based on the hypothesis being true is low
Ho is outside the confidence interval
statistically significant
What does it mean if p>0.05?
we cannot reject Ho, within the confidence interval and not statistically significant
How do we work out the lower limit?
observed value / error factor
How do we work out the upper limit?
observed value x error factor
What happens as we get more data?
error factor gets smaller and confidence interval narrows
How do we recruit people in cohort studies?
recruit outcome-free individuals and classify them into exposed and unexposed
What are the types of cohort study?
prospective/concurrent and retrospective/historical
What does internal comparison refer to?
Comparison of sub-cohorts
What does external comparison refer to?
Comparison of study group to external reference population.
Advantages of cohort studies
can study a range of different outcomes, rare exposures and establish exposure precedes outcome
Disadvantages of cohort studies
expensive (large and resource intensive), time consuming, risk of high number of losses (->survivor bias), not good for rare outcomes
What are the Koch’s postulates for?
rules used to determine if an infectious agent is the cause of a disease
What are the 3 rules of Koch’s postulates?
the organism occurs in every case of the disease
the organism occurs in no other disease
on removal from the body and growing in pure culture it can induce the disease anew
What are the problems with Koch’s postulates?
definition of the disease
difficulties isolating the microbe
no model for examination as cannot ethically transmit a microbe into a healthy human or animal
What measures can help prevent infection spreading?
protective isolation for susceptible people
preventative isolation for people with the infection
hand washing
antibiotic restriction
try to keep staff to a particular area of the hospital
What is Ro?
The rate at which an individual infection produces new infections in an individual.
What is the formula for Ro and define the constituents?
Ro = betaXD
beta = capacity for transmission X = number of infectious individuals D = time period of infectivity
What are the results for Ro and interpret them?
Ro > 1 : infection propagates
Ro
How do we begin a case-control study?
find 2 groups of people: one group have the disease (cases) and the other doesn’t (controls) then ask all individuals in groups if they were exposed or unexposed
What is a nested case-control study?
A case control study within a cohort study
What 2 types of bias are case-controls most prone to?
selection bias and recall bias
What are the 9 Bradford Hill Criteria for Causality?
strength of association specificity of association consistency of association temporal sequence dose response reversibility coherence of theory biological plausability analogy
Define epidemiology
The study of the distribution and determinants of health related states or events in specified populations, and the application of this study to the control of health problems.
What is the hierarchy of evidence with the best evidence at the top?
systematic reviews randomised control trials cohort studies case-control studies cross-sectional surveys case reports
Define clinical trial
Any form of planned experiment which involves patients and is designed to find out the most appropriate method of treatment for future patients with a given medical condition.
What is the purpose of a clinical trial?
To provide reliable evidence of treatment efficacy and safety.
Define efficacy
The ability of a health care intervention to improve the health of a defined group of people under specific conditions.
What problems would a non-randomised control trial have?
allocation bias and confounding
How do we conduct a randomised control trial?
identify a source of eligible patients invite them and gain consent randomly allocate patients to treatments follow up in identical ways minimise losses maximise compliances
What does open label mean?
The study has not used blinding.
When is blinding difficult?
surgical procedures
alternative medicine
lifestyle interventions
prevention programmes
What is the problem with comparing a treatment with no treatment?
We cannot be sure whether the observed difference is due to the new treatment or just because the group were receiving care.
What is the placebo effect?
Even if the therapy is irrelevant to the patient’s condition, the patient’s attitude to their illness, and the illness itself, may be improved due to a feeling that something is being done about it.
Define placebo
An inert substance made to appear identical to the active formulation. Used to cancel out any placebo effect.
What is As-Treated Analysis?
You only measure the outcomes of the people who took their medication as instructed.
What is Intention-To-Treat analysis?
You measure everyone’s outcome whom you intended to treat whether they took their medication as intended or not.
What are the effects of As-Treated analysis?
randomisation is lost, selection bias (non-compliers are likely to be systematically different) and confounding
What are the 4 ethical principles?
beneficence (helps them)
non-maleficence (does no harm)
autonomy (patient’s decision)
justice (non-discriminating)
Define clinical equipoise
There is reasonable uncertainty or ignorance about the best treatment.
What are the features of a narrative review?
biased, subjective and based on the view of one expert
What are the features of systematic reviews?
other people look at the evidence, unbiased and objective
explicit, transparent and reproducible
Define meta-analysis
A quantitative synthesis of the results of 2 or more primary studies that addressed the same hypothesis in the same way.
How are studies weighted in a meta-analysis?
according to size and uncertainty of odds ratio
In a Forest plot, what is the size of the square proportional to?
Weight given to the study
How is the null hypothesis shown on a Forest plot?
a line that runs vertically (solid or dashed)
What should all studies in a meta-analysis be similar in?
study design participant profile treatments/exposures outcomes measured statistical analysis used
What does a Fixed Effects Model assume?
That the studies are estimating exactly the same effect size.
What does a Random Effects Model assume?
That the studies are estimating similar, but not the same, effect sizes.
Which of FEM and REM has the more evenly distributed weights?
Random effects model (REM)
In which of FEM and REM is the confidence interval usually wider?
random effects model (REM)
What is publication bias?
Larger studies or studies with statistically significant results or ‘favourable’ results are more likely to be published.
What do we plot on a funnel plot?
results of studies against their size
What do funnel plots test for and what are the results?
test for publication bias, if funnel shaped then there is no evidence of bias
What is heterogeneity?
How different the studies within a meta-analysis are. Ideally we want very little heterogeneity within our meta-analysis.
