Explain the sources and hierachies of evidence
- Evidence?
- What is it?
- How good is it?
- Where can it be found?
- Diagnosis – The process of determining the nature of a patient’s disorder by considering the signs and symptoms, the medical background and where needed the results of tests and or/investigations
- Prognosis – An assessment of the future course of a patient’s disease based on the knowledge of the course of disease in other patients as well as factors such as age, gender and general health of the patient
- Treatment Decision – A choice of what action to take to treat a patient
- Theories of decision-making
- Normative – What should you be doing?
- Descriptive – What are you doing?
- Prescriptive – How can you improve what you are doing?
- Diagnostic Reasoning - The most common area of research in medical decision making
- Focusses on how doctors make decisions
- Often compares “expert” clinicians with “novice” ones
- Hypothetico-Deductive Model - Cue acquisition - Hypothesis Formation
- Cue interpretation - Hypothesis
- Evaluation
- Research suggests that the Hypothetico-Deductive model is used either by
inexperienced clinicians or by experienced ones with a problem they don’t recognise. - Normally experienced clinicians are more likely to use Pattern Matching.
- The Prospect Theory
- Decisions are divided into two parts:
- Framing and Editing – The preliminary analysis of the decision problem
- Phase of Evaluation – Framed prospects evaluated and the prospect with the highest value selected
- Decision Process - May be influenced by how the decision is framed
- May be influenced by people’s values or beliefs associated with the benefits and risks of
different options and outcomes
- Evidence - Any factor than can and should influence clinical decision making
- Results of rigorous clinical trials and studies i.e. information research studies.
- How good is evidence?
- Matching the research evidence to the area you want to address
- “Heirarchy of Evidence” lists sources in order of their perceived ability to provide quality
evidence that can be used in practice
- Hierarchy Of Evidence
a) N of 1 randomised trials
b) Systematic review of randomised trials
c) Single randomised trial
d) Systematic review of observational studies
e) Single observational study
f) Physiologic studies
g) Unsystematic clinical observations - Where can good evidence be found?
- Cochrane reviews
- Evidence based journals
- Medline and other databases
- When sources of research evidence are organized into a ‘hierarchy’ what is the basis for this order? Resistance to bias.
Identify the role of random sampling and the implications of sampling variation.
- What are the important design features of a representative sample? A sample that has approximately the same distribution of characteristics as the population from which it was drawn.
- Do you understand the terms: sampling frame, random sample, stratified sample?
- *Random Sample** - A random sample is one where the researcher insures (usually through the use of random numbers applied to a list of the entire population) that each member of that population has an equal probability of being selected
- *- Stratified Sample** - A sample selected from a population that has been stratified, with a sample selected independently in each stratum. The strata are defined for the purpose of reducing sampling error.
- Sampling Frame – The potential sources from which the sample is drawn
- What factors should influence how large a sample needs to be?
Time, money, resources in general. Availability of subjects. Importance of trial.
- Standard deviation: A measure of how widely dispersed are the individual observations in a distribution. The standard deviation is the square root of the variance.
- Standard error: The standard deviation of the sampling distribution of a sample statistic such as a mean or a difference between proportions.
How do you interpret a 95% confidence interval?
- Do you understand why results drawn from samples are presented with confidence intervals? Confidence interval: An interval with given probability (e.g. 95%) that the true value of a parameter such as a mean, difference between proportions or risk ratio is contained within the interval. To allow you to decide what is statistically significant.
- What is the difference between a 50%, 95%, 99% confidence interval? Difference between one, two and three standard deviations from the original data.
Outline the process of hypothesis testing and interpret p-values.
- Hypothesis: An idea expressed in such a way that it can be tested and refuted.
- Null hypothesis: The hypothesis that there is no difference between two groups. Statistical methods look for evidence against the null hypothesis by calculating a P value.
- P value: The probability that the difference between groups would be as big as or bigger than that observed, if the null hypothesis of no difference is true. The smaller the P value, the stronger is the evidence against the null hypothesis of that there is no difference between the groups.
- Type 1 Error - Represented by the Greek letter alpha, the Type 1 error is the chance of accepting the research hypothesis when the null hypothesis is actually true (“false positive”).
- Type 2 Error - The chance of accepting the null hypothesis when the research hypothesis is actually true (“false negative”).
Identify the public health implications of obesity.
- How do we measure and define obesity, energy intake, energy balance? Clinically overweight is a BMI over 25 and below 30. Clinical obesity is a BMI greater than 30.
- What are the health consequences of being overweight? Increased risk of cardiovascular disease, increased risk of stroke, increased risk of Type II NIDDM, increased risk of certain types of cancer (breast, uterus, colonic etc) increased risk of osteroarthritis and gout. Stigma and labeling.
- What is BMI, how is it calculated and interpreted? BMI is Body Mass Index. BMI is calculated by dividing a person’s weight (in kilograms) by his or her height (in meters, squared). BMI below 16 is severe starvation. 20-25 is healthy. 25-30 is overweight. 30+ is obese.
- What are current trends in obesity, why have they occurred? Obesity is increasing, particularly amongst children. Lack of physical exercise, changes in eating habits and the reliance on television and video games for childminding.
- What approaches are there to addressing obesity at an individual and population level?
Health promotion on a national level. Changes in school dinners. Advertising low salt in diets. Health promotion in schools and from GPs. Weight Watchers. Government dietary advice. Dieticians in primary care and hospitals.
- What is currently understood as a ‘healthy diet’ in adulthood? A healthy diet is a diet that does not contain excessive quantities of fat, sugar or salt, and that provides enough vitamins and minerals for the body to function at peak efficiency. To this end, the consensus is that you have to eat five portions of fruit and vegetables per day.
Describe the economics and ethics of healthcare rationing.
- Why is rationing of healthcare inevitable? There are not and never will be enough resources to satisfy all human wants and desires
- Scarcity – Small and inadequate amount
- Opportunity Cost - The cost of passing up the next best choice when making a decision.
- For example, if an asset such as capital is used for one purpose, the opportunity cost is the value of the next best purpose the asset could have been used for.
- Cost-Effectiveness – The usefulness derived from expenditure per unit spent.
- What is a Quality Adjusted Life Year (QALY)? Quality-adjusted life-year. Calculated by multiplying the change in utility value (overall measure of a patient’s perception of well-being) conferred by an interventional therapy by the expected duration of the treatment benefit or harm.
- What do you need to measure to calculate a QALY? The change in utility and the expected duration of benefit or harm.
- How can QALYs be used in making rationing decisions? The greater the number of QALYs can be used in comparison with opportunity cost.
