JISCMail - EVIDENCE-BASED-HEALTH Archives

Accept my apologies that I have not read the actual paper, but I think this might help. My understanding of the situation is this:

1 NNTs and NNHs are derived from the event rates.

2 Event rates are estimates taken from observations in a sample, so confidence intervals should be calculated from them.

3 If the difference in event rates between two groups (in this case steroid injection and control) is statistically non-significant, then any other estimates derived from them will be non-significant.

4 Therefore, if the difference in event rates is non-significant, there is no point in calculating the CI for NNH or any other derivative, you know that the result will be non-significant.

It is not so much a question of SHOULD, more a question of WHY BOTHER?

If you want to play around with numbers (forgive me if I make too much of an assumption), you could do this:

1 To get the lower confidence limit of the NNH, take upper limit of the Risk Difference or Absolute Risk Increase and invert it

2 To get the the upper confidence limit of NNH. take the lower limit of the Risk Difference or Absolute Risk Increase and invert it

3 The interval between the two will include zero.

On 9 May 2014, at 00:37, Mark Ayson <[log in to unmask]> wrote:

Dear Colleagues

Should numbers-needed-to-harm require a confidence interval? And if the adverse event rates from which the NNHs are calculated have a confidence interval crossing the line of no effect and the NNH have the same, how do you interpret the results?

I have a study that states: Because of the large and non-significant confidence intervals around the steroid injection adverse event rates, confidence intervals were not reported for the NNH, as proposed by McQuay and Moore

The study is: Gaujoux-Viala C, et al. Efficacy and safety of steroid injections for shoulder and elbow tendonitis: a meta-analysis of randomised controlled trials. Ann Rheum Dis 2009;68(12):1843-9.

I look forward to your replies

Regards

Mark

Mark Ayson MBChB DPH
Research Advisor, ACC
Tel (04) 816-6386 / Ext 46386
ACC / Research / Justice Centre - Level 7
PO Box 242 / Wellington 6011 / New Zealand / www.acc.co.nz

ACC cares about the environment – please don’t print this email
unless it is really necessary. Thank you.

Disclaimer:
"This message and any attachments may contain confidential and privileged information.
If you believe you have received this email in error, please advise us immediately by
return email or telephone and then delete this email together with all attachments.
If you are not the intended recipient, you are not authorised to use or copy this message
or any attachments or disclose the contents to any other person. "



			Mark Ayson MBChB DPH Research Advisor, ACC Tel (04) 816-6386 / Ext 46386 ACC / Research / Justice Centre - Level 7 PO Box 242 / Wellington 6011 / New Zealand / www.acc.co.nz ACC cares about the environment – please don’t print this email unless it is really necessary. Thank you.