Although I am no expert in psychometrics, in most cases a trait does not have different scales to measure it's two sides. So I would say that you can use the existing scales.

If you score high on one of the scales you mentioned, you are towards the slow strategy. If you score low you are toward a fast LHS. So you shouldn't need a separate scale in theory.

This paper compares the existing scales: http://www.sciencedirect.com/science/article/pii/S0191886913013251

I don't know of any such scale. I think the underlying assumption is that fast and slow are on a single continuum. If you are interested in the sexual aspect of a fast strategy, you can use the Sociosexual Orientation Inventory (Simpson) or the Revised Sociosexual Orientation Inventory (Penke).

thanks for the answers so far! when i take a look at the mini-k items, i don't think that a low score will represent a r-strategy (of course to some extent, but it should be possible to get a better instrument for r-strategy). there may be too much vagueness or there may be other explanations than a fast LHS for a low score.

i'd rather compare this issue to the measurement of collectivism and individualism. These two are also not just 2 poles on one continuum but are each measured with seperate scales!

and thanks for the paper (although i have them all :-), and the hint concerning the SOI - this is interesting and i've already planned to use it for a study but as you said it's not that broad but just for some aspects.

I haven't had success with the Mini-K before so I am not advocating for it, but the core idea of fast vs. slow assumes a single continuum. It might be, however, that the tools we have are more effective at measuring one end of this continuum. Personally, I am unhappy with how this construct is operationalized in the social science literature.

yes, there are Problems with that scale, at least psychometric ones. but it's the most common short scale (the other short scale - hkss - has Problems too and does measure something different to some extent).

of course there are other possibilities to measure LHS, e.g. by asking respondents about the first sex Age, how many children they plan to have, how old they expect to become, and many other questions like this. but a standardized psychometric scale would be fine...

Sexual history and attitudes are covered to some extent by the SOI, and you can probably augment it with some items from other scales. Age of first sex can be somewhat erratic as a measure of life-history. There are many irrelevant factors that go into that. So is number of children, for the same reason. I like to focus more on psychological dispositions, such as how many life-time sexual partners a person would like to have.

The lack of an r-scale has been a sore spot for some in our research group for some time. I know of no such measure. I would also be careful of mixing proximate psychological processes with less proximate LH outcomes. The Copping et al. (2014) criticism, makes a valid point regarding the relationship between psychometric measures and biometric indicators (I think that the outright dismissal of self-report measures is simply wrong, but I can see how one can have that approach ).

I know that AJ's preferred method is using the MiniK, TIPI, SF36, and HKSS to create a "SuperK" factor, but that doesn't address your question. Unfortunately, most of the research on r/K is done on college student or volunteers, which will tend toward being slower almost by definition. 

I'm kind of rambling, so I'll stop. I do think the question is a great one and someone should definitely get on it (benchmarking it against the K measures).

 As an aside, you can find a recent meta analysis of the Mini-K in the attached link. 

 Raf

http://www.apa.org/pubs/journals/features/ebs-h0099837.pdf

Rafael, thank you for sharing your thoughts and linking the meta-analysis paper. I was not aware of it. I have been giving this issue some thought recently, and discussed it with several members of our evolutionary group in UMN. We might try to do something about it in the future, time permitting, although I doubt we will go for a MINI-K type scale.

A.J. is working on a rejoinder to the Copping critique that ought to frame the underlying issues well. Unfortunately, it's being met with some resistance. I will let you know if anything come of it.

Thanks!