5. intro to Evidence Based Medicine

Question 1

what is Evidence-Based Medicine

Answer 1

the integration of BEST RESEARCH EVIDENCE with CLINICAL EXPERTISE and PATIENT VALUES

(dave sackett)

Question 2

how can EBM help you

Answer 2

• make better clinical decisions
• share decision making with patients
• provide better diagnostic reasoning
• understand benefits vs harms
• practice more safely

Question 3

4 STEPS of EBM

Answer 3

1. Formulate an Answerable QUESTION
2. Track down the BEST EVIDENCE
3. critically APPRAISE the EVIDENCE (find out how good it is)
4. APPLY the EVIDENCE (integrate results with clinical expertise and patient values)

Question 4

what PRINCIPLE do we use when FORMULATING AN ANSWERABLE QUESTION and TRACKING DOWN EVIDENCE

Answer 4

PICO

• POPULATION/PATIENTS
• INTERVENTION (exposure, test)
• COMPARISON/CONTROL
• OUTCOME

Question 5

what are the most common type of CLINICAL QUESTION about

Answer 5

how to TREAT a disease

treatments and therapies are called INTERVENTIONS

(but not all questions are about interventions)

Question 6

DIFFERENT TYPES of Clinical QUESTIONS require..

Answer 6

DIFFERENT TYPES of RESEARCH EVIDENCE

Question 7

a CROSS-SECTIONAL / PREVALENCE study is a study in which information is collected in a planned way in a defined population..

Answer 7

AT ONE POINT IN TIME

Question 8

what is a RANDOMISED CONTROLLED TRIAL (RCT)

Answer 8

an EXPERIMENTAL STUDY where participants are randomised either to receive the NEW INTERVENTION being tested OR receive a CONTROL TREATMENT (standard treatment or PLACEBO)

Question 9

APPRAISAL of any study must consider:

Answer 9

• VALIDITY
  can the results be trusted?
• RESULTS
  what are the results?
  how are they (or can they be) expressed?
  what do they mean?
• RELEVANCE (step 4 of EBM)
  do these results APPLY to the local context

Question 10

2 TYPES of VALIDITY

Answer 10

INTERNAL VALIDITY
- are the results of the study CORRECT for the people in the SAMPLE

EXTERNAL VALIDITY
- if so, does the sample REPRESENT FAIRLY in the kind of PATIENTS in MY PRACTICE

Question 11

INTERNAL VALIDITY is determined by..

Answer 11

how well the DESIGN, DATA COLLECTION and ANALYSES are carried out

THREATENED by BIASES

Question 12

EXTERNAL VALIDITY assumes…
and is a matter of..

Answer 12

ASSUMES INTERNAL VALIDITY

is a matter of PERSONAL JUDGMENT

Question 13

a SAMPLE is used to..

Answer 13

MAKE INFERENCE about the POPULATION

Question 14

What is a RANDOM (sampling) ERROR

Answer 14

the answer may differ from the truth when taking several different samples from the population

by CHANCE the people used are different from average so result will be different

Question 15

the best way to MINIMISE RANDOM SAMPLING ERROR is to

Answer 15

INCREASE SAMPLE SIZE

Question 16

what are 2 METHODS of ASSESSING the ROLE of CHANCE

Answer 16

P-VALUES (HYPOTHESIS TESTING)

CONFIDENCE INTERVALS (ESTIMATION)
(more informative)

Question 17

what is a HYPOTHESIS

Answer 17

a statement about a POPULATION PARAMETER (such as a population proportion or population mean) or some other characteristic of a population

Question 18

HYPOTHESIS
is it EASIER to PROVE or DISPROVE a statement

Answer 18

DISPROVE is easier

Question 19

2 competing Hypotheses

what is a NULL HYPOTHESIS (H0) and ALTERNATIVE HYPOTHESIS (H1)

Answer 19

NULL
- there is NO ASSOCIATION (/no diffference) between X and Y

PRESUMED to be TRUE unless the data gives strong EVIDENCE AGAINST it

ALTERNATIVE
- there IS an ASSOCIATION/difference between X and Y

Question 20

STEPS in HYPOTHESIS TESTING

Answer 20

1. state the NULL & ALTERNATIVE HYPOTHESES
2. Decide what STATISTICAL TEST is appropriate
3. Use the test to CALCULATE the P-VALUE
4. WEIGH the EVIDENCE AGAINST the NULL

Question 21

how to address if a result is a CHANCE finding (by chance)

Answer 21

calculate a TEST STATISTIC and its corresponding P-VALUE

Question 22

what is a P-VALUE

Answer 22

a PROBABILITY (lies from 0 to 1)

• comes from a STATISTICAL TEST testing the null hypothesis
  (start by assuming the null is TRUE)

measures the strength of the evidence AGAINST the null

Question 23

what is used as the CUT OFF for a P-VALUE to REJECT the NULL hypothesis

Answer 23

0.05 / 5%

if P LESS than or EQUAL TO 0.05 then REJECT NULL HYPOTHESIS

if P GREATER than 0.05, DO NOT REJECT

Question 24

the SMALLER the P-VALUE..

Answer 24

the STRONGER the EVIDENCE AGAINST the NULL HYPOTHESIS

Question 25

2 possible of a Hypothesis Test

Answer 25

• REJECT NULL HYPOTHESIS
• DO NOT REJECT NULL HYPOTHESIS (can not say ‘accept’)

Question 26

what is a TYPE I ERROR in a Hypothesis Test result

Answer 26

FALSE NEGATIVE

INCORRECTLY REJECTING the NULL
H0 is actually not rejected
(innocent)

Question 27

what is a TYPE II ERROR in a Hypothesis Test result

Answer 27

FALSE POSTIVE

INCORRECTING FAILING TO REJECT the NULL
H0 should

Question 28

what is a STATISTICAL POWER and how is it calculated

Answer 28

CORRECTLY REJECTING NULL (H0)

the PROBABILITY that a test will find a statistically signicant difference when a difference really exists

(probability of correctly finding that H0 is FALSE and a difference does actually exist)

POWER = 1 - TYPE 2 ERROR

Question 29

if a statistical test result is ‘Not statistically significant’ what does it mean

Answer 29

there is INSUFFICIENT EVIDENCE for a DIFFERENCE or effect

(does NOT mean ‘no difference/effect’)

Question 30

what happens to P-VALUE as the SAMPLE SIZE INCREASES

Answer 30

DECREASES

Question 31

what is a better way of expressing UNCERTAINTY

Answer 31

CONFIDENCE INTERVALS

Question 32

what are CONFIDENCE INTERVALS (CI)

Answer 32

a way of showing the UNCERTAINTY SURROUNDING a POINT ESTIMATE (sample statistic = point estimate of a parameter) by giving an INTERVAL (range) of LIKELY VALUES where the TRUE POPULATION VALUE IS LIKELY TO LIE

WIDER CI = MORE UNCERTAINTY
indicates the estimate is imprecise

Question 33

by convention we usually quote …% CONFIDENCE INTERVALS

Answer 33

95%

Question 34

What does a 95% CONFIDENCE INTERVAL mean

Answer 34

if we were to repeat the study many timeswith different samples, 95% of the 95% CIs would contain the true value
/
we are 95% CONFIDENT that the true value in the population lies within this range

Question 35

what CLINICAL IMPLICATIONS can be derived from the CI

Answer 35

the UPPER and LOWER LIMITS provide a way of assessing whether the results are CLINICALLY IMPORTANT

Question 36

what can you also check within your CI

Answer 36

if a HYPOTHESISED VALUE (ie Null value) for the population parameter falls within the confidence interval.

if so, our results are consistent with the hypothesised value

if not, it is unlikely that the parameter has this value.