95% Bootstrap Confidence Interval PreviousNext
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 Estee posted on Wednesday, October 16, 2013 - 6:22 am

I tested a mediation model. The indirect effect was bootstrapped. The 95% confidence limit was [.000, .038]. According to literature, an indirect effect is considered sig. if the CI does not include/cross zero. Is the .000 showed in the results really equal to zero or it may be for example.0001 ? so, how to confirm whether the 95% confidence limit [.000, .038] is sig or not?

Thanks very much.
 Linda K. Muthen posted on Wednesday, October 16, 2013 - 3:57 pm
I would count that as non significant even if the value was .0001. With so many tests being performed, I would be conservative.
 Joao Garcez posted on Friday, March 13, 2015 - 10:27 am

I was wondering something similar. I have a non-significant indirect effect (b = -.019, p>.05) with the following bc bootstrap 95% CI: ( -.047 - .002 ).

Is a value of .002 considered to be equal to zero?

Also, when values in the lower and upper bound have opposite signs like the one above, does it mean something? The path above is negative with a positive value in the CI. Does it mean is non-significant?

Thank you very much.
 Bengt O. Muthen posted on Friday, March 13, 2015 - 12:22 pm
If the CI covers zero, the coefficient is deemed insignificant. Your lower limit is negative and your upper limit positive, so your coefficient is non-significant.
 Joao Garcez posted on Tuesday, March 17, 2015 - 2:34 am
Thank you for the clarification.

 Rosie Essery posted on Thursday, April 07, 2016 - 8:42 am
Hi there,

I too have a similar query - I have a non-significant indirect effect (B = 0.153, p = .104), but then the 95% BCa CI is [0.032 , 0.417].

I'm a but confused as to whether this is a significant mediation or not - the CI would suggest yes, but the p value no?

Would appreciate any advice - many thanks!

 Linda K. Muthen posted on Thursday, April 07, 2016 - 8:52 am
If the confidence interval and p-value do not agree, you must not have a symmetric confidence interval.
 Rosie Essery posted on Thursday, April 07, 2016 - 9:26 am
Thank you for the very quick response!

I would agree that the confidence interval is asymmetric - looking at my data, the point estimate doesn't sit in the centre of the BCa confidence interval.

Does this mean that it is not meaningful to interpret this in the normal way, i.e. 0 not being between the lower and upper bounds of the confidence interval as a sign of significant mediation?

Many thanks for your helpful advice.

 Bengt O. Muthen posted on Thursday, April 07, 2016 - 10:02 am
The non-symmetric CI is interpreted the same way: If 0 is not within the interval then the effect is significant.
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