the science of EBM

Question 1

what are the different types of observational study?

Answer 1

• case control
• cohort
• cross sectional

Question 2

what are examples of experimental studies?

Answer 2

• randomised and non randomised trials

Question 3

what are the principle of evidence based medicine?

Answer 3

1) patient dilema
2) ask
3) acquire
4) appraise
5) apply
6) act and asses.

Question 4

what are examples of reviews?

Answer 4

• expert opinion
• systemic review
• meta-analysis

Question 5

what are the 8 levels of evidence?

Answer 5

Question 6

what are 5 factors that might decrease the quality of evidence?

Answer 6

• study limitations
• inconsistency of results
• indirectness of evidence
• imprecision
• publication bias

Question 7

what are 3 factors that might increase the quality of evidence?

Answer 7

• large magnitude of effect
• plausible confounding, which would reduce a demonstrated effect
• dose response gradient

Question 8

what are the advantages of case studies?

Answer 8

• quick and cheap to conduct
• rapid publication
• early indications of problems
• can help detect new drug side effects and potential uses

Question 9

what are the 4 disadvantages of case studies?

Answer 9

• statistically weak
• no control group
• vert small numbers of patients
• cases may not be generalised to the wider population

Question 10

wha are the advantages of cross sectional survey?

Answer 10

• cheap and simple
• ethically safe
• useful for planning purposes

Question 11

what are the disadvantages of cross sectional study?

Answer 11

• cause and effect?
• volunteer bias
• unequal distribution of confounders

Question 12

what are 2 complications that may arise in studies?

Answer 12

confounders = uncontrolled extraneous variables
- observation, smokers tend to have smaller babies than non smokers

SPURIOUS ASSOCIATION
- it understand harmful to the foetus?
= - initial studies showed that babies exposed to ultrasound has a lower birth weight
- later studies failed to confirm this observation.

Question 13

how do case control studies work?

Answer 13

Question 14

advantages of case control studies?

Answer 14

• youcan look at multiple rosk factors at once.
• good for studying rare conditions or diseases with long latent period
• useful as initial studies to establish an association
• do not require a long follow up period

Question 15

disadvantages of case control study?

Answer 15

• retrospective study which relies on patient recall to determine exposure or patient records
• confounders
• selection of control group is difficult
• unlikely to detect rare causes of disease

Question 16

how does a cohort study work?

Answer 16

Question 17

what are the advantages of cohort study?

Answer 17

• ethically safe
• subjects can be matched
• can show cause precess the effect
• easier and cheaper than a randomised controlled trial

Question 18

what are the disadvantages of cohort study?

Answer 18

• high drop out rate
• exposure may be linked to hidden confounder
• blinding is difficult
• outcome of interest may take a long time to occur

Question 19

how does a randomised controlled trial work?

Answer 19

Question 20

how does a double blind method work?

Answer 20

Question 21

design modifiers:
single blind?
double blind?
cross over?
placebo controlled?

Answer 21

Question 22

design features of clinical research:
parallel group comparison?
paired (matched) comparison?
within subject comparison?

Answer 22

Question 23

advantages of randomised controlled trial?

Answer 23

• unbiased distribution of confounders
• clearly identified populations
• randomisation helps statistical analysis
• more likely to be blinded

Question 24

disadvantages of randomised controlled trial?

Answer 24

• expensive
• volunteer bias
• ethical issues if treatment group are seen to respond badly or better than expected

Question 25

what are the 5 problems associated with RCT's?

Answer 25

- impossible = with treatments for very rare disease where the number of patients is too limited - unnecessary = when a treatment produces a 'dramatic' benefit - imatinib for chronic myeloid leukaemia - stopping trials early= interim analysis of trials is now commonly undertaken to assess whether the treatment is showing benefit if the trial can be stopped early - resources = the costs of RCT's are substantial in money, time and energy - generalisability = RCT's are often carried out on specific types of patients for a relativey short period of time.

Question 26

how do you establish cause and effect?

Answer 26

1) is the association due to a chance occurrence? 2) is it due to a flaw in the methodology? 3) is it due to another factor which is linked to both the exposure and the outcome

Question 27

what is the Bradford Hill criterion linking smoking to lung cancer?

Answer 27

Question 28

what are the advantages and disadvantages of expert (narrative) review?

Answer 28

advantages = comprehensive survey , answers a specific question disadvantages = expert bias

Question 29

what is a systematic review?

Answer 29

a systematic review attempts to identify, appraise and synthesise all the empirical evidence that meets pre- specified eligibility criteria to answer a given research question. - it is a comprehensive literature search that identifies all similar and relevant studies that satisfy pre-defined: - inclusion criteria - exclusion criteria

Question 30

how do researchers conduct a systematic review to minimise bias?

Answer 30

researchers conducting systemic reviews use explicit methods aimed at minimising bias, in order coproduce more reliable findings that can be used to inform decision making.

Question 31

describe the vitamin C for preventing and treating the common cold study?

Answer 31

Question 32

how do you practise EBM?

Answer 32

- craft a clinical question - search the medical literature - find the study that will best answer the question - perform a critical appraisal - determine how the results will help you care for your patient - evaluate the results in your patient or population

Question 33

how can you identify different trials?

Answer 33

Question 34

why are systematic review views as the gold standard?

Answer 34

because the avoid/minimise bias

Question 35

what are the advantages of systematic review?

Answer 35

- uses explicit and reproducible methodology - many different studies can be compared and contrasted directly with each other to determine the overall findings - reduces bias as it takes into account the range of views and findings - less costly to review previous studies than to initiate a new study

Question 36

what are the disadvantages of systematic review?

Answer 36

- dependant on screening strategy - can be hard to compare results of studies that have completed in very different ways - publication bias - very time consuming

Question 37

what is met analysis?

Answer 37

combine qualitative and quantitive study data from several selected studies to develop a single conclusion that has a greater statistical power.

Question 38

4 stages of meta analysis

Answer 38

1) establish statistical significance with studies that have conflicting results 2) develop a more accurate estimate of effect magnitude 3) provide a more complex analysis of harms , safety data and benefits 4) examine subgroups with individual numbers that are not statistically significant

Question 39

advantages of meta analysis

Answer 39

- greater statistical power - greater ability to extrapolate to the general population - statistical analysis is more objective than narrative analysis - more effect to present a combined result.

Question 40

disadvantages of met analysis

Answer 40

- individual studies do not necessarily all use the same methodology - heterogeneity of study populations - requires advanced statistical techniques - very time consuming