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For a mediation analysis in JASP (using bias-corrected percentile bootstrapping).

For the Indirect effect, I have a situation where:

the p-value is significant (< 0.05),

BUT where 0 is found within the range of the 95% Confidence Interval.

So, these contradict. And so, I am unsure what to take from this.

In this scenario, is there statistical evidence for an indirect (mediation) effect or not?

• This is strange. In fact, it should not happen, because a 95% CI contains all the values that would not be rejected using an alpha=5% test. The conflict could be due to the noise in the bootstrap...can you provide a concrete example so we can reproduce this?

Cheers,

E.J.

• Hi Michael_Jasper,

This is a good question, and I understand your confusion here. The reason why the results can contradict in this case, is because the p-value comes from a different test, and not form the (bias-corrected percentile) bootstrap. The p-value is based on the standard errors that are computed using the so-called Delta method (this is listed in the footnote under the table). Hence, the s.e. and p-value are the ones from the 'Standard' method. If you want to test your indirect effect using a bias-corrected bootstrap (which I would advise you to do as well, since it is known to outperform the delta method) you should just report the point estimate and the 95% C.I. Since in your case the interval contains zero, you cannot reject your Null-Hypothesis that there is no indirect effect.

Best,

Michael

• RE: you said:

"you should just report the point estimate and the 95% C.I.".

Ok, understood. Although if I wanted a p-value from these values, is this possible? If so, how can I get it?

• So, I use Percentile bootstap. And report the Estimate and the Confidence Interval (CI). But NOT the given p-value because, as said above, it comes from using a different method.

But if I wanted a p-value for the actual Estimate and CI produced by the Percentile bootstrap method. Would the method described in this paper be appropriate/valid?

https://www.bmj.com/content/343/bmj.d2304