The choice of a method is inevitably a compromise between generality with precision on the one hand and trainability for a low execution error rate on the other. ACH is a good compromise, teachable in a week. I accept that no method can be perfect and that there will always be the need for experienced review, so that a huge investment in a notionally better method may not actually be worthwhile. However, my judgement is that there is a niche for an upgraded ACH ‘ACH+’ that is reliable for a wider range of situations. The extensions that I see can be grouped under:
- removing the restrictions on the hypotheses
- providing support for the proper determination of likelihood
- consequential changes to the interface, to maintain ease of use.

http://conferences.computer.org/vast/vast2007/ shows the use of formal logics followed by ACH, but the use of ACH can also stimulate the use of formal logics in the search for new or modified hypotheses. Ideally, I would see formal and empirical logics combined, with a natural to-ing and fro-ing until one has satisfactory hypotheses. A fully extended ACH (‘ACH++’?) would need to accept ‘plug-in’ formal logics. In particular, ACH may show that the evidence is inconsistent with all current hypotheses. Formal logics could then be used to suggest variants. For example, AM could be used to identify an assumption that ‘Iraq’s actions are generally in line with Saddam’s public statements’, which (if this leads to an inconsistency) suggests the hypothesis ‘Saddam is deliberately misleading in his public statements’ by quasi-negation.

The use of ACH with what you call indicators is already seen by many practitioners as part of the use of ACH, although maybe not part of ACH itself. I’m not sure. But ACH+ would need to support this too.

My main contentions are:
- much of the criticism of ACH is ill-founded
- where it is well-founded, ACH has some ‘stretch’ potential.

Regards
Dave

I agree that AM can complement ACH, but not by generating hypotheses. AM does not in any way help generate hypotheses any more than ACH does. Both techniques presuppose the ability to generate hypotheses. There are other techniques to help with that.

I see AM as a later stage than ACH in the thinking process. ACH gives you the focal hypothesis – the one that best survives the process of elimination. AM then asks, “But how good is the case for it?”, since failure to falsify (at the end of ACH) isn’t the same thing as evidential support, only consistency. AM can help uncover important gaps in the evidence, and identify what assumptions are being made along the way.

Two questions:

1. What kind of extensions would ACH+ incorporate?

2. Does anyone out there use ACH not just with existing evidence but with what we might call indicators – i.e. “what would I expect to see if this [hypothesis] were the case”? Is that the kind of thing that might go into ACH+? (It could be incorporated into AM.)

Yanna

As ACH gets more popular, criticism and suggested improvements abound. You raise an important topic. According to Heuer, though, the key consideration is “the relative likelihood of each hypothesis”. This would seem to rule out many of the suggested interpretations and variants, and avoid their errors. Heuer says “The matrix should not dictate the conclusion to you.” He does acknowledge that simply operating his method without regard to his cautions can lead to error, and gives some guidance.

I agree that in (all too common) complex situations inexperienced users will need experienced guidance, but isn’t this at least implicit? It is also true that at first ACH seems tedious, but with experience one can take short-cuts, and as long as one understands that one is concerned with relative likelihoods, this is perfectly safe.

Argument Mapping (AM) is a form of formal reasoning. Its use would thus complement ACH’s empirical approach, for example by helping to generate hypotheses. As Heuer says: “It is useful to make a clear distinction between the hypothesis generation and hypothesis evaluation stages of analysis.”

My own view is that it would be helpful to develop some extensions to ACH (“ACH+”) that deal ‘out of the box’ with some common problems, whilst retaining the validity of being linked to likelihood and hence empirical logic. One could then get a balance between simplicity and applicability.

An interesting piece. Some of my thoughts below.

1. Too many judgments to make

This doesn’t strike me as a problem inherent in the matrix structure. It’s a problem inherent in any analytic method. Analysis does just that: break down global judgments into multiple smaller judgments. If you didn’t consider all of those e/h combinations, you’re not fully analysing. This is true in a hierarchical map format, too, if you’re fully analysing. So changing the format doesn’t change the number of judgments.

You may, of course, decide to leave things out of a map (just you may decide to leave things out of a box). But if this is by decision rather than by thoughtlessness/accident, then you’d be making a judgment anyway (to leave it out or enter it in).

2. No e is an island

OK, so sometimes you have to justify a matrix rating because otherwise it looks mysterious. How often does this happen? We could easily modify the matrix to cope with it; e.g., where an additional premise is required:

– Reformulate the evidence to incorporate that premise/auxiliary information; OR
- If the problem occurs only in one cell, write the additional information (the argument supporting your judgment) in that cell, e.g. by adding a footnote.

We fill in the gaps with auxiliary information all the time, even in argument mapping. Most people operate like this most if not all of the time – and manage to make judgments, even good ones! I suspect that the number of times this became a crucial issue in ACH is small, and so a slight modification such as occasional footnoting would take care of it.

3. Flat structure of hypotheses

There is a genuine challenge here, but not with the matrix per se. It’s about the right level of granularity at which it’s useful to start any such process.

Heuer says (I think – or is this something I’ve found useful?) to ensure hypotheses are mutually exclusive and at the same level of abstraction/granularity. But what level is that? Ultimately, a hypothesis is likely to be quite a complex story, e.g. addressing the “Who, what, where, when, how and why” of an action or event. But starting with that degree of detail across the board can be wasteful and tedious, while starting too “high up” can be pointless, confusing and/or misleading (more on this later). If you can start high up and eliminate top-level possibilities (e.g. you can eliminate murder) then you’ve saved a lot of work. But sometimes that’s not possible. Identifying the right level at which to start is difficult.

Again, however, I don’t think this is a problem with a matrix format per se. It’s about what to put into the matrix. A hierarchical map structure confronts this problem in a different way, but no less awkwardly. For example, should the hypothesis “Prescribe antidepressants together with counselling” be at the same level as, or below, the hypotheses “Prescribe antidepressants” and “Prescribe counselling”? Conceptually they should be at the same level, but doing that results in duplication of work. It’s more practical to make it subordinate to one of the others, thereby doing violence to The Order of Things…

3.a The problem has worse implications for AM

Note that ACH may fare better than AM (Argument Mapping) in an important respect related to this issue. Contrary to AM, which focuses on support or corroboration, ACH is a process of falsification. This means that, under certain circumstances, getting the level of granularity wrong in ACH is less misleading than getting it wrong in AM. For example, if you formulate the hypothesis as “Diana was murdered” (without specifying by whom or why), multiple bits of evidence can be consistent with that hypothesis, but each of those might be consistent with only some particular sub-hypothesis (that specifies a culprit). In ACH, the effect would simply be to keep the “murder” hypothesis alive (unfalsified) – but in AM it would look like lots of actual support – even though any particular murder hypothesis would not be poorly supported. Cognitively speaking, believing she was murdered on poor grounds (AM) seems worse than simply failing to dismiss the possibility (ACH). This, of course, applies only if users don’t misuse ACH matrices. I’m quite sure that, regardless of the fact that it’s the contradictions that count, people find it difficult NOT to read consistency as support. Now that might be a drawback of ACH, but one that’s easily dealt with by not distinguishing between consistency and neutrality – but that’s another story.

I won’t tackle this here, but I suspect that things get even nastier if you consider evidence that’s mutually incompatible, i.e. sets where e1 supports/is consistent with h1a but is incompatible with h1b, e2 is consistent with h1b but inconsistent with h1a, and so forth, where h1a and h1b are both subordinate to (sub-hypotheses of) h1; e.g. h1a is assassination by MI5 and h1b is murder by a crazed bystander, and h1 is murder.

4. Subordinate deliberation

Any analytic method is a precision tool, not a Swiss army knife. That’s why we need a whole toolkit. This is not a problem. It’s essential to analysis, which, by definition, breaks down complex processes into discrete steps in order to make the process more rigorous and thereby (hopefully) minimise error. If a tool did everything, it’d be as complex as the process.

I don’t see why, therefore, you should be able to do something with ACH that another tool is better for.

What might genuinely be useful is a way to rate the reliability of evidence in a highly visible fashion. But we could introduce a convention into ACH, such as colour-coding of evidence and impacts, to show reliability. (The grounds for that judgment could then be shown in an argument map – perhaps hyperlinked to the table entry.)

5. Decontextualisation and discombobulation

Even in argument mapping we take a whole lot of context for granted – even when we articulate co-premises. I had a shock a while ago when I decided to take a map regarding a particular country and substitute a fictional country’s name. All of a sudden, things didn’t make any sense! I realised how much contextual historical knowledge about the relationships between countries like Iran, the US and Russia came into play in understanding the original map. Ordinarily, to have added all that as co-premises would have been madness. Context is ineliminable.

In the Hicks example, I would argue that there is insufficient granularity in the specification/description of the evidence. The claim “Hicks was captured in Afghanistan” is inappropriate or insufficiently refined, to do the job that’s asked of it. Again, it’s not the matrix that’s at fault but the way the information is entered.

SUMMARY

1. Does ACH ask us to make too many distinct judgments?

ACH asks us to make the same number of distinct judgments as any analytic method that’s equally thorough. What’s “too many”? If it’s laborious, that’s the cost of analysis. The only time the judgments are “too many” is when the incremental error resulting from the number of judgments is greater than the degree of error arising out of the global judgment. Perhaps what we want, for practicality, is a degree of analysis that gives enough improvement in hit rate with the least amount of effort/boredom. That might be a different tool.

2. Are ACH judgments emaciated due to the stripping away of relevant context, of both hypotheses and evidence?

If they’re emaciated, I doubt this has much impact except in a very restricted number of cases. In those cases, we can address this easily by expanding the technique in a simple ways, as outlined.

OTHER PROBLEMS WITH ACH?

There are other problems with ACH. I mention some here briefly. Note that these may also be true of maps.

1. Malleability of hypotheses and evidence

Given that in many real-life cases from the human domain (as opposed to the laboratory) judgments of support/consistency/opposition don’t rely on direct evidence but on murkier facts or more indirect evidence (e.g. that someone has a motive is not clear-cut evidence for murder or against suicide), we can all too often interpret or reinterpret either the evidence or the hypothesis to make them consistent. This is a great feature of conspiracy theories: you tell a sufficiently convoluted story, you can just about make anything consistent with it. How useful is ACH in such contexts?

2. Invisibility of aspect

This is something that was pointed out to me in the US: If all the evidence corroborates only one part/aspect of a hypothesis, the matrix makes this invisible.

My thoughts: Does it matter? Only if we read consistency as support – a dangerous thing anyway. It’s a worse problem for rough argument mapping, which really does show it as support…

3. Invisibility of source

Also from the US: What if all evidence (or all inconsistent evidence) comes from the same source or is of the same source type (e.g. imaging)? The matrix doesn’t show that either.

My thoughts: Perhaps a simple device (like the bases in argument maps) could take care of the source type issue.

CONCLUSION

I’m not convinced that the matrix is a problem. But given that both ACH and AM are considered laborious – too analytic – to use, perhaps a tool that’s less analytic would do well. However, you’d have to show that the tool made a significant improvement to judgments, for the time and effort it demanded, compared to an intuitive, more global, or less technologically supported judgment.

That’s it for now!