measures of association

Question 1

what types of studies are medical research studies?

Answer 1

they are RCTS, case-control and cohort

Question 2

how are outcomes measured?

Answer 2

a variety of ways - categorical (positive or negative), continuous subjective measures such as pain, and continuous objective measures such as HbA1C

Question 3

what are measures of association for?

Answer 3

the effect of new treatments with dichotomous outcomes

Question 4

how can the measures of association be measured?

Answer 4

relative risk, risk difference or odds ratio - they will show the direction and magnitude of association between variables

Question 5

what is probability?

Answer 5

it is the measure of chance of getting the outcome of interest from an event

Question 6

what is the equation for probability?

Answer 6

it is the number of times the outcome of interest occurs / the total number of outcomes possible

Question 7

how do you calculate the percentage chance?

Answer 7

it is the probability x 100

Question 8

what is risk?

Answer 8

it is a way of expressing treatment effects - it is the probability of an event occurring

Question 9

how do you calculate absolute risk?

Answer 9

the number of events / the number of people at risk

Question 10

what is relative risk?

Answer 10

it is the ratio of the risk of an event in a particular group e.g. exposed in one group compared to the risk of outcome in an unexposed group (in RCTs - treatment group compared to the control group)

Question 11

what traditionally is the numerator?

Answer 11

the group of interest. The denominator is the unexposed or control group

Question 12

explain RR = 1?

Answer 12

it means that the risk of outcome is the same in the exposed as the unexposed group

Question 13

explain RR <1 and RR>1?

Answer 13

RR<1 means that the risk of outcome in the exposed group is less than the risk in unexposed and >1 means that the risk of outcome in the exposed group is higher than that in the unexposed group

Question 14

what is the range for ratio values?

Answer 14

0 to infinity

Question 15

how would you obtain percentage reduction?

Answer 15

subtract the RR from 1 and x100

Question 16

what does a large value of RR imply?

Answer 16

it implies a strong association - must always be interpreted in association with the confidence interval

Question 17

what is the odds?

Answer 17

it is the probability of the event occurring / the probability of the event not occurring - number of times event happens / number of times it does not

Question 18

what is the odds ratio?

Answer 18

it is the odds of the event in one group / the odds of the event in another group (exposed/unexposed)

Question 19

what does OR = 1 mean?

Answer 19

the odds in the exposed group is the same as the odds in the unexposed group

Question 20

what is 95% CI used for?

Answer 20

it is used to estimate the precision of the OR and the RR

Question 21

what does a large CI mean?

Answer 21

low precision of RR or OR

Question 22

what does the CI crossing 1 mean?

Answer 22

there is not statistical significant difference between the two groups - exposed and unexposed

Question 23

why should RR not be used in retrospective or case control studies and what are they used in?

Answer 23

they are not used in these because they are not meaningful - the proportion of cases or control is chosen by the researcher. They are used in RCTs, cohort and prospective studies

Question 24

what would you use in case-control or retrospective?

Answer 24

OR - commonly reported in logistic regression analysis

Question 25

what happens if the disease is rare?

Answer 25

RR and OR are similar

Question 26

what is the risk difference?

Answer 26

it is the difference in risk of outcome in the exposed and unexposed or treatment and control group

Question 27

what would a difference of 0.48 mean?

Answer 27

there is a 48% increased/decreased risk for developing outcome for one of the risk factors or variables

Question 28

what is useful about RD?

Answer 28

it is meaningful to find out if findings from a study are worthy of being incorporated into clinical practice - magnitude of risk difference may or may not warrant changing practice

Question 29

what is NNT and what is it used for?

Answer 29

it is number needed to treat and it is a way of evaluating the clinical importance of treatment in practice

Question 30

how do you calculate NNT?

Answer 30

1/RD

Question 31

when is NNT used?

Answer 31

in studies comparing an intervention and standard treatment

Question 32

how would we describe NNT simply?

Answer 32

it is the number of people that need too receive a treatment in order to see the desired effect in at least one of them

Question 33

how would CI contraindications relate to medical practice?

Answer 33

if there was a contradictory measurement in CI such as crossing 1 then would be concerned. Likewise be concerned with your diagnosis if the consultant would have diagnosed with something different 95% of time

Question 34

what are CI?

Answer 34

they are values to show that 95% of the time a mean will lie in this range

Question 35

what is the p value?

Answer 35

it is the probability of a coefficient being at least as big as yours - assuming the coefficient is 0

Question 36

what does a small p value represent?

Answer 36

the zero-assumption is probably wrong and then effect is likely and vice versa for a large p value - evidence is not strong enough to suggest an effect

Question 37

how would you carry out statistical process?

Answer 37

observe, guess, test, assess

Question 38

what is R squared?

Answer 38

how good the fit of the model is - how well the points align to the line of best fit

Question 39

what is S?

Answer 39

it is the deviation of the points