Evidence Based Dentistry Flashcards
What does ‘risk’ mean?
- What are the chances of something happening
- Good or bad
What does ‘outcome’ mean?
- ‘something’ that might happen (what you are actually mea suring)
- Could be something good or bad
What are statistics?
- Numbers that summarize information
- The chances that an outcome will happen
What are statistics based on?
- Observations of a large number of people
What are statistics useful for?
- Predicting what is likely to happen in the future
- Risk statistics
What way are statistics usually formatted?
- As fractions
For binary events, what do statistics express the chance o f?
- Express the chance of being in one of 2 states
What is risk equal to in fraction form?
Number of events of interest/total number of observations
What are ‘odds’ equal to in fraction form?
Number of events of interest/number without the event
What questions should you ask when interpreting risk? (4 points)
- Risk of what?
- How big is the risk?
- Does the risk information reasonably apply to me or my patient ?
- How does this risk compare with other risks?
When thinking about the question ‘risk of what?’ when interpreting risk, what should you be thinking about?
What is the outcome?
- Getting a disease
- Dying from a disease
- Developing a symptom
- Surviving a disease
When thinking about the question ‘how big is the risk?’ when interpreting risk, what should you be thinking about? (3 points)
- What are the chances of experiencing the outcome?
- Out of how many?
- What is the timeframe? next year? next 10 years? lifetime?
When thinking about the question ‘Does the risk information reasonably apply to me or my patient?’ when interpreting risk, what should you be thinking about? (3 points)
- Age
- Sex
- Lifestyle
When thinking about the question ‘How does the risk compare with other risks?’ when interpreting risk, what should you be thinking about?
- Perspective - which risk should I do something about?
- (very personal decision)
What questions should you as when you see messages about risk reduction? (5 points)
- Reduced risk of what?
- How big is the risk reduction?
- Does the risk reduction information reasonably apply to me?
- Any downsides?
- Is the benefit (risk reduction) worth the downsides?
When thinking about the question ‘Reduced risk of what?’ when you see messages about risk reduction, what should you be thinking about? (2 points)
- What outcome?
- How much do you care about it?
When thinking about the question ‘ How big is the risk reduction ?’ when you see messages about risk reduction, what should you be thinking about? (2 points)
- What are my chances if I don’t get the treatment?
- Starting and modified risks
When thinking about the question ‘ Does the risk reduction information reasonably apply to me? ‘ when you see messages about risk reduction, what should you be thinking about?
- Is the study based on people like you or your patient?
When thinking about the question ‘ Any downsides? ‘ when you see messages about risk reduction, what should you be thinking about? (4 points)
- Life threatening disease
- Time
- Cost
- Hassle
In drug studies, what are the STARTING and MODIFIED risks?
- The chances of the outcome in the UNTREATED and TREATED groups (those who did not take the drug and those who did)
What is a pilot study?
- Not a main study (Happens prior to the main study and probably uses fewer people in it than what is needed for a proper study)
What is a contingency table?
- A table showing the distribution of one variable in rows and another in columns, used to study the correlation between 2 variables
What is relative risk?
- Used to compare the risk in two different groups of people
What is absolute risk?
- Your risk of developing the disease over a time period
What does NNT mean?
Number needed to treat
What is meant by ‘number needed to treat’?
- The number of patients you would need to treat to prevent one patient from developing the disease/condition/outcome
Numerically what is NNT?
1/absolute risk difference
What value would the risk ratio be if the risks on both groups were equal?
1 (value of no difference)
What value would the odds ration take if there was no benefit of paracetamol over placebo?
1 (value of no difference)
What is a confidence interval?
- Tells us the range of values that a true population treatment effect is likely to lie
- A range of values so defined that there is a specific probability that the value of a parameter lies within the value
What does a confidence interval that embraces/overlaps/contains/straddles the ‘value of no difference’ between treatments indicate?
- That there is INSUFFICIENT EVIDENCE for a difference between the treatment and control group in the POPULATION
For a ratio, what is the ‘value of no difference’?
- 1
If the confidence interval does not embrace/overlap/contain/straddle 1 (the value of no difference) what does this mean?
- That there is sufficient evidence to suggest that there is a difference
If the CI for the difference does not overlap 0, what is there sufficient evidence for?
- A difference between 2 values in the population
What are observational uncontrolled studies? (3 points)
- Researchers watch what happens to a group of people
- A group of patients has a disease A which is treated with drug X
- The researchers observe how may get better
What are controlled studies? (2 points)
- Cohort or case control
- Researchers observe what happens to people in different situations - without intervening
What are randomized controlled trials? (2 points)
- Patients randomly split into 2 groups - one gets intervention, the other gets placebo
- Any differences at follow up caused by intervention
What is a case report/case study?
- A report on a single patient or series of patients with an outcome of interest
Has a case report/study got a control group?
- No, no control group involved
What are case report/studies used for? (2 points)
- Identify new disease outcome
- Hypothesis generation
What are 2 disadvantages of case report/studies?
- Cannot demonstrate valid statistical associations
- Lack of control group
What is a cross-sectional study?
- The observation of a defined population at a single point in time
- Exposure and outcomes are determined at the same time
What are cross-sectional studies used for? (2 points)
- Estimating prevalence of disease
- Investigate potential risk factors
What are the disadvantages of cross-sectional studies? (3 points)
- Causality
- Confounding
- Recall bias
What is a case control study?
- The study of people with a disease and a suitable control group of people without the disease
- Looks back in a time at exposure to a particular risk factor in both groups
What are case control studies used for?
- Looking at potential causes of disease
What are the disadvantages of case control studies? (4 points)
- Confounding
- Recall/selection bias
- Selection of controls
- Time relationship (did exposure occur before disease?)
What is confounding?
-Occurs when the experimental controls do not allow experimenter to reasonable eliminate plausible alternative explanations for an observed relationship between independent and dependent variables
What is the process of a cohort study? (4 points)
- Establish a group of individuals in a population
- Measure exposures
- Follow up over a period of time
- Identify those that develop the disease (outcome of interest)
What are cohort studies used for? (4 points)
- Estimating the incidence of a disease
- Investigating the cause of a disease
- Determining prognosis
- Timing and direction of events
What are the disadvantages of a cohort study? (5 points)
- Controls difficult to identify
- Confounding
- Blinding difficult
- For rare diseases - need large samples
- Very expensive/time consuming
What are randomized controlled studies sometimes referred to as?
- Clinical trials
Which kind of trial/study is considered the ‘gold standard’s study design and why?
- Randomized controlled trials
- For effectiveness and efficacy
- Provides the strongest evidence on effectiveness of treatments
What are the 4 design elements of randomized controlled trials?
- Specification of participants (inclusion/exclusion criteria)
- Control/comparison groups
- Randomisation
- Blinding/masking
Randomisation in trials is used to minimise bias. What do groups can be affected by this?
- Older patients
- Patients with more severe disease
What does random allocation of participant to the treatment ensure?
- Each individual entered into the trial has equal chance of being allocated to any treatment arm (active treatment/placebo)
What should be used to ensure the allocation of active treatment/placebo to participants is completely randomised?
- A computer
What is allocation concealment?
- A technique used to prevent selection bias by concealing the allocation sequence from those assigning participants to intervention groups, until the moment of assignment. Allocation concealment prevents researchers from (unconsciously or otherwise) influencing which participants are assigned to a given intervention group
What are the disadvantages of randomised controlled trials? (5 points)
More difficult to design and conduct that observational studies:
- Ethical issues
- Feasibility
- Costs
- Still some risk of bias and generalisability often limited
- Not suitable for all research questions
What is the outcome of a RCT?
- What is measured to assess whether the intervention/ new drug/ new treatment/ new technique was effective/worked
