I guess that you mean a comparison of the near to mid term mortality risk associated with

    MUAC < 125 mm & WHZ > -2 (MAM MUAC-only)

and:

    MUAC < 115 mm & WHZ > -3 (SAM WHZ only)

I alos assume tha you want mortality in untreated cases found in the community.

Looking at the literature you will probably find results for

    all MUAC < 125 mm
    
and:

    all WHZ < -3
    
which will not answer your (very specific) question. Looking at the literature that reports results from community-based cohort studies we find that all WHZ did not work well at predicting near to mid term mortality in all cohorts. You can see this in this review:

    Pelletier, D. L. (1994). The relationship between child anthropometry and mortality in developing countries: implications for policy, programs and future research. The Journal of Nutrition, 124(10 Suppl), 2047S–2081S.

I have put this review here.

I have some data here from 11 countries collected in cohort studies running between between 1977 and 1997 and could run a bespoke analysis to answer your specific question. I would need to seek permission form the data owners to do this.

Sorry not to be of more help.

Something maybe a bit more updated....

Schwinger C, Golden MH, Grellety E, Roberfroid D, Guesdon B. (2019). Severe acute malnutrition and mortality in children in the community: Comparison of indicators in a multi-country pooled analysis. PloS one, 14(8), e0219745. https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0219745

Thanks both.

Mark - you have correctly interpreted my question.

Anonymous - thanks for sharing the link.  Findings from this analysis found children identified as having SAM by only MUAC <115mm had a similar hazard of death as those identified with only a WHZ <-3. 

Until more research is available I assume from this that WHZ-only SAM has higher hazard of death than MAM-only MUAC.

thanks again