A randomised controlled trial examining a treatment for septic shock reports the following results:

"At 90 days after randomization, 27.9% patients who had been assigned to receive the treatment had died, as had 28.8% who had been assigned to receive placebo (odds ratio 0.95; 95% confidence interval [Cl], 0.82 to 1.10; P value= 0.50)."

a) Explain the meaning of the underlined terms. Interpret the result of the trial.

(40% marks)

Odds ratio: The odds of a patient in the treatment group dying within 90 days divided by the odds of patients in the placebo group dying within 90 days.

95% confidence interval: The range of values which is 95% certain to contain the population parameter of interest (in this case, Odds Ratio)

P Value: The probability of obtaining the observed, or more extreme results, assuming the null hypothesis is true.    (3 marks)

## Discussion

In case it matters to anybody, in this SAQ the examiners are using the findings of the ADRENAL trial (Venkatesh et al, 2018)

Odds ratio:

• The Odds Ratio represents the odds that an outcome will occur given a particular exposure, compared to the odds of the outcome occurring in the absence of that exposure.
• An OR =1 suggests there is no association.
• If the CI for an OR includes 1, then the OR is not significant (i.e. there might not be an association)

Confidence interval:

• The range of values within which the "actual" result is found.
• A CI of 95% means that if a trial was repeated an infinite number of times, 95% of the results would fall within this range of values.
• The CI gives an indication of the precision of the sample mean as an estimate of the "true" population mean
• A wide CI can be caused by small samples or by a large variance within a sample.

p-value:

• The probability of the observed result arising by chance
• The p-value is the chance of getting the reported study result (or one even more extreme) when the null hypothesis is actually true.

Interpretation of results:

• The OR is so close to 1 that there is probably no association if the results were significant, i.e. there is no treatment effect detected here.