The results of a randomisedcontrolled trial failed to show a statistically significant effect of the intervention compared to placebo. The trial was well-conducted and well-designed with a recruitment target based on a sample size estimation done in advance.

What should we conclude about the null hypothesis of no difference between the groups in the primary outcome?

1. The null hypothesis is false (this trial result was a Type II error)
2. The null hypothesis is true (the intervention does not work)
3. We don't know if the null hypothesis is true or if this trial result was a Type II error
4. You should do a post-hoc power calculation to confirm that the null hypothesis is true