We have recently conducted a cluster analysis for an open card sorting task in which 19 experts grouped 112 items each. We achieved decent silhouette values for the cluster analysis but have been asked by reviewers to provide evidence that the number of experts we used was sufficient for this task (I think they are expecting something kind of power analysis).
We have used Kendall's Coefficient of Concordance to examine the concordance in individual sort patterns between participants (this came out as .25), but it seems they want something more. After looking around I cannot find anything which might suggest a suitable sample size or even that sample size is not important and I'm pretty sure power analyses don't apply for cluster analysis. Is there anything I can report to show my sample size is sufficient (or not if the case may be)? I am using R to analyse the data.
BTW by sample size I mean number of participants not number of items included in the cluster analysis.