Clinical Trials- measurement

Question 1

Outcome measures

Answer 1

-Categorical

-Continuous

Question 2

Categorical (qualitative) measures

Answer 2

1. Nominal: named categories (ex. dead/alive)
2. Ordinal: ordered categories (ex. cancer stages)

Question 3

Continuous (quantitative) measures

Answer 3

1.Discrete: only integers (counts)

2. Continuous: any numerical value (rectal temp, blood glucose)

Question 4

Clinical effect size

Answer 4

Difference between means and medians. Need to determine if it is clinically significant
-evaluate with continuous outcomes. Put into means and medians
-also should have 95% CI to measure uncertainty

ex. Blood glucose of two groups. Find avg in each group. Difference between them= clinical effect size

Question 5

P value chance vs effect

Answer 5

Tells us chance of getting result BUT does not tell us anything about its actual effect

Question 6

Pinkeye study in Beef Cattle

Answer 6

-randomized at start; each groups were equal
-P value showing how much you would expect to see by chance.
-no difference between vaccines and placebo= fail to reject Ho

Question 7

Measurement w/ categorical variables

Answer 7

-Many clinical trials that deal with disease use an outcome measure that is categorical
>Mortality: sick or not; morbidity: dead or alive

Question 8

What needs to be explored when using categorical variables?

Answer 8

1. How to measure the frequency of the health outcome event in trial
2. How to measure the magnitude of the effect (impact) of the treatment or interventions

Question 9

Relative risk

Answer 9

-index of strength of the association between the exposure and the disease (observational study)
vs.
-index of the magnitude of the clinical effect of treatment (clinical trials)

Question 10

Relative risk eqn

Answer 10

RR= Risk in controls/risk in treated

Question 11

RR >1

Answer 11

Means controls are at a greater risk of disease and the treatment groups is protected by treatment

Question 12

RR<1

Answer 12

Means controls are at a reduced risk of disease and treatment may actually make disease worse

Question 13

RR=1

Answer 13

Means there is no treatment effect

Question 14

Attributable Fraction

Answer 14

-measure of clinical significance, often used with vaccines

“what proportion of disease in the untreated animals could have been prevented by vaccine/treatment?”

ex. 2 died in vaccine group; 4 died in control
AF=50%… 2 of control likely would have be saved

Question 15

Absolute risk reduction

Answer 15

Amount by which your therapy reduces the risk of a bad outcome

ARR=RR(control)- RR (treatment)

Question 16

Number needed to treat

Answer 16

Different way of expressing Absolute risk reduction or risk difference. Looking at the number of patients needed to treat to prevent one additional bad outcome

NNT=1/ARR

Question 17

Odds Ratio

Answer 17

An estimate of relative risk
-tends to overestimate relative risk
-used more in observational studies, less likely in clinical trials

-Odds of exposure in the diseased group divided by the odds of exposure in the control group

Question 18

Chi-squared test

Answer 18

-need Ho
-can look for expected values if there is no effect of treatment
-chi squared statistic which is compared with chi square table, to get P value
-if RR is not statistically significant then difference in risk is likely due to chance

Question 19

Confidence intervals

Answer 19

-Number obtained when conducting a clinical trial a large number of times, that is 2 standard errors of the true mean
>will include true mean or true relative risk 95% of the time

**indicates the level of uncertainty around the measure of clinical effect

Question 20

CI powers

Answer 20

Small study= low power, wide Cl

Large study= high power= narrow CI

Question 21

Confidence interval crossing 1

Answer 21

implies no statistical difference for the estimate of relative risk

Question 22

95% confidence interval

Answer 22

-useful in negative results
-P-value greater than 0.05, it doesn’t tell us anything about the power of the trial. Could be due to trial been too small. Would want CI to be small to indicated high power trial.

**width of CI gives idea of precision of RR estimate

Definition: 95% of the time, true value will lie within those numbers. Upper end will place the treatment as the most favourable