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BDS2 - PMHP > Evidence Based Dentistry > Flashcards

Evidence Based Dentistry Flashcards

1
Q

define risk

A

what are the chances?

can be good or bad

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2
Q

define outcome

A

something that might happen
what you actually measure
to do with statistics and epidemiology

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3
Q

what are statistics

A

numbers that summarise information
based on observations of large number of people
useful in predicting what is likely to happen in the future
the chance that an outcome will happen
use fractions = differences between 2 numbers

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4
Q

what is the numerator

A

top number in a fraction

number of people who actually experience the outcome

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5
Q

what is the denominator

A

bottom number in fraction

number of people who could potentially experience the outcome

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6
Q

what are risks and odds

A

ways of expressing chance in numbers

for binary events - they just express the chance of being in one of the 2 states

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7
Q

define risk in terms of numbers

A

number of events of interest / total number of observations

usually expressed as % or by saying the risk of the event happening was number in number eg one in four

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8
Q

define odds

A

number of events of interest / number of observations minus the event
usually not expressed as a %
the chances of the event were fraction of the chances of not the event eg one third of the chance

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9
Q

what questions should you ask to interpret risk?

A

risk of what?
- what is the outcome

how big is the risk?

  • what are the chances
  • out of how many
  • what is the time frame

does the risk apply to me / my patients

  • age
  • sex
  • lifestyle

how does this risk compare with other risks
- perspective

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10
Q

what questions should you ask when you see messages about risk reduction?

A

reduced risk of what?

  • what outcome
  • how much do you care

how big is the risk reduction

  • what are my chances without treatment
  • starting and modified risk

does the risk reduction information reasonably apply to me
- similar people to you / patients

what are the downsides

  • side effects
  • time
  • cost

is the benefit worth the downsides

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11
Q

what are the starting and modified risks in drug studies

A

the chances of the outcome in the untreated and treated groups (those who did not take the drug and those that did)

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12
Q

what is another name for a 2 x 2 table

A

contingency table

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13
Q

explain what a pilot study is

A

not a main study
usually conducted with fewer people than needed
information gathered from these is not enough to take practice

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14
Q

explain the differences between study groups

A

sorry i couldn’t think how to word this better but
need to have 1 group as a control for the comparison
need to have the other group that is exposed to the treatment you are studying

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15
Q

what does the control group using the placebo show

A

starting risk

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16
Q

what does the treatment group undergoing the study show

A

the modified risk

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17
Q

what is the absolute risk reduction

A

difference in risk between groups

find risk in both groups then take them away from each other

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18
Q

what value would the absolute risk difference take if there was no benefit of the tested group over placebo?

A

0 = value of no difference

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19
Q

define number needed to treat (NNT)

A

the number of patients you would need to treat to prevent one patient from developing the disease / condition / outcome

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20
Q

define number needed to treat numerically

A

1 / absolute risk difference
always round up
result is the number of people you need to treat for 1 person to notice the difference

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21
Q

what is the risk ratio

A

how many times more likely is the result in one group than the result in the other group
= risk of test group / risk in placebo group
answer is how much more likely test group is than plan placebo group

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22
Q

what value would the risk ratio take if the risks in both groups were equal? ie no benefit of the test group over the placebo group

A

1 = value of no difference

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23
Q

define odds ratio

A

ratio of odds of the result in both the test group and placebo group (usually intervention / control)

24
Q

what value would the odds ratio take if there was no benefit the test group / intervention group over the placebo?

A

1 = value of no difference

25
Q

can the risk ratio and odds ratio be used interchangeably?

A

people do use these interchangeably
however odds ratio only approximates risk ratio when the outcome is rare
odds ratio tends to over estimate the risk ratio

26
Q

what do confidence intervals tell us

A

the range of values that a true population treatment effect (eg risk ratio) is likely to lie (subject to a number of assumptions)
they quantify the level of uncertainty for the population on interest

27
Q

explain what confidence intervals reveal in relation to the risk ratio

A

a confidence interval that contains the value of no difference (which is 1 for ratio ratios) between treatments indicates that there is insufficient evidence for a difference between the treatment and control group in the population
if the confidence interval does not contain 1 then there is sufficient evidence to suggest there is a difference
(look at examples in lectures to understand the wording of these)

28
Q

explain confidence intervals in relation to the absolute risk difference

A

it is the same as the risk ratio except instead of 1 being the number it is 0
ie if the intervals contain 0 there is insufficient evidence to suggest a difference

29
Q

what is fundamental to research

A

basic science

30
Q

should we always trust studies that have only been proven in animal or lab studies

A

no

  • be sceptical
  • don’t assume if there is a positive benefit that will help you / your patients
  • treatments that work in animals often dont have the same result in people eg dolly the sheep
31
Q

name the 3 different types of study designs in human research

A
  • observational uncontrolled studies
  • controlled studies
  • randomised controlled studies
32
Q

what happens in observational uncontrolled studies

A
  • researchers watch what happens to a group of people
  • no intervening or experimental treatment
  • was it treatment that reached the outcome or was it something else that would have happened anyway - you can’t tell
33
Q

what happens in controlled studies

A
  • cohort or case control

- researchers observe what happens to people in different situations without intervening

34
Q

what happens in randomised control trials

A
  • patients randomly split into 2 groups
  • 1 group receives intervention
  • the other group gets placebo
  • reveals that any differences between the groups at follow up has to be caused by intervention
35
Q

list the evidence levels from worst to best

A
  • ideas, editorials and opinions
  • case series and case reports
  • ecological studies
  • cross-sectional studies
  • case-control studies
  • cohort studies
  • randomised control studies
  • systematic reviews and META analysis
36
Q

explain case report / case series

A
  • a report on a single patient o series of patients with an outcome of interest
  • no control group
37
Q

what are case report / case series studies used for?

A
  • identifying new disease outcome
  • hypothesis generation
  • used in clinics when you see a patient presenting with unusual conditions you would write it up the be able to share it with colleagues
38
Q

what are the disadvantages of case report / case series studies?

A
  • cannot identify valid statistical associations
  • lack of control group
  • worst evidence level / bottom of hierarchy
39
Q

explain cross sectional studies

A
  • the observation of a defined population at a single point in time (or time interval)
  • exposure and outcome are determined at the same time
40
Q

what are cross sectional studies used for

A
  • estimating prevalence of a disease
  • investigate potential risk factors
  • one time opportunity study
41
Q

what are the disadvantages of cross sectional studies

A
  • causality
    > finding relationship between 2 factors but can’t tell if they influenced each other as it is only a snapshot of time
  • confounding
    > measuring one thing but what is underlying it is a whole other set of behaviours that goes alongside it
  • recall bias
    > patient may not remember
42
Q

explain case control studies

A
  • the study of people with a disease and a suitable control group for people without the disease
  • looks back in time at exposure to a particular risk factor in both groups
  • starts with the cases and controls and looks back and compares
43
Q

what are case control studies used for

A
  • looking at potential causes of disease
  • useful in rare diseases as you can recruit cases and study retrospectively rather than start with a group of healthy patients and wait for them to develop a disease they might never develop
44
Q

what are the disadvantages of case control studies

A
  • confounding
  • recall / selection bias
  • selection of controls
    > different professionals may not agree on when to identify the disease
    > what about the patients who are borderline having the disease who are then included in the control group
  • time relationships
    > did exposure occur before the disease
  • hard study to complete well
45
Q

explain cohort study

A
  • establish a group of individuals in a population and measure exposures (questionnaires, clinic check ups etc)
  • follow up over a period of time
  • identify those who develop disease over this period of time
46
Q

what are cohort studies used for

A
  • estimating incidence of disease
  • investigating causes of disease
  • determining prognosis of disease
  • time and direction of events
    > know exactly when exposure occurs and when disease occurs
47
Q

what are the disadvantages of cohort studies

A
  • controls difficult to identify
  • confounding
  • blinding difficult
  • need a large sample of people for rare diseases
  • very expensive / time consuming
48
Q

define incidence

A

number of new cases over time

need to have a duration

49
Q

explain randomised control trials

A
  • sometimes called clinical trials
  • gold standard study design
  • provides strongest evidence on effectiveness of treatment
  • have 2 treatment groups at a base line and have follow up and measuring of outcomes
50
Q

name the 4 design elements of randomised control trials

A
  • specification of participants
    > inclusion / exclusion criteria
  • control / comparison groups
    > placebo
  • randomisation
    > separate sample into 2 groups fairly and randomly
    > differences between the 2 groups should be random ie not selecting healthy people to get good results to promote new drug
  • blinding / masking
    > person who administers treatment doesn’t know what they are giving
    > patient doesnt know what they are getting
    > analyst doesnt know who is in what group
    > no one can affect data
51
Q

why do we need a control group

A
  • people often get better on their own

- need to confirm is the improvement natural or is it actually to do with the treatment of the study

52
Q

how should randomisation be done

A
  • computer
    > no one has influence over allocation
    > ensures everything should be fairly balanced
53
Q

what is allocation concealment (selection bias)

A

A technique used to prevent selection bias by concealing the allocation sequence from those assigning participants to intervention groups, until the moment of assignment
ensures the researchers can’t influence the participants

54
Q

what is important in blinding / masking

A
  • the placebo should be identical
55
Q

what are the advantages of RCTs

A
  • provide strongest and most direct epidemiological evidence for causality
56
Q

what are the disadvantages of RCTs

A
  • difficult to design
    > ethical issues
    > feasibility
    > costs
  • still some risk of bias and generalisability often limited
    > if exclusion / inclusion criteria is too specific it cannot be relevant to your practice
  • not suitable for all research questions
  • non blinded RCTs may over estimate treatment effects

BDS2 - PMHP (11 decks)

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