The lethality of the attempt may be a good measure of "the actuality of the suicide attempt." This reference is old but still worth a look:

Smith et al. (1984) Lethality of suicide attempt rating scale

http://www.ncbi.nlm.nih.gov/pubmed/6528343

There is a big difference between suicidal intent, suicide risk, the ability to predict a suicide attempt, the ability to predict suicidality, and the potential lethality from any suicide attempt.  The responses in this thread suggest to me that these concepts are being confused for one another. 

I will be the first to say that it is simply impossible to predict either suicidality or a suicide attempt on an individual level.  While we may like to be able to predict suicidality on an individual level it is not possible and many years have been spent with this as the focus of research.  (I believe that researchers need to focus on better understanding the phenomenology of suicidality before putting more effort in to this prediction.)

Second, suicidal risk is also impossible to accurately gauge.  One of the suicidality scales I consulted on, the Sheehan-Suicidality Tracking Scale (S-STS), purposely does not look at 'suicide risk'.  The Clinically Meaningful Change Measure (CMCM) version of the S-STS does have a place where a clinician can document their "Judgement of Suicide Risk", but the judgement of risk is different from the actual risk itself.  Using the phrase "suicide risk" suggests that the clinician can see into the future to give an accurate representation of the likelihood a patient will make a suicide attempt (and / or kill themself as a result of a suicide attempt).  In my opinion, documenting anything by labeling it as "suicide risk" would open up the clinician to the potential of lawsuits as such phrases suggest they are deluding themself about their ability to predict the course of a patient's suicidality.  In contrast to this, the phrase from the S-STS CMCM (clinician's "judgement of suicide risk") clearly illustrates that the clinician understands they are only documenting a judgement of risk and not the actual level of risk.  (See the first link for an overview of the Sheehan-Suicidality Tracking Scale.)

The potential lethality from a suicide attempt is different from all of the previously mentioned items.  The potential lethality from a suicide attempt is the likelihood a patient will end up dying if they engage in a suicide attempt.  Again, this is an attempt to see into the future and give an accurate representation of the severity of injury that would result from said hypothetical suicide attempt and the likelihood they would live even if they incurred said injury.

Entirely separate from all of these things is the concept of suicidal intent.  A patient can experience low suicidal intent while all of the previously mentioned concepts are considered higher.  For example, a patient with schizophrenia may experience a command hallucination telling them to kill themself.  Said patient may be perceived as being at a higher likelihood of making a suicide attempt and / or dying as a result of a suicide attempt than a patient not experiencing said hallucinations.  However, the patient may have absolutely zero intent to act on said suicidal hallucination and absolutely zero intent to die from a suicide attempt. 

It is also possible for a subject to experience a heightened suicidal intent with little actual risk for harm.  For example, a child watches the movie Snow White with their family.  His older brother offer him an apple that the brother says is like the one in the movie.  Thinking that the apple would kill him (since it put Snow White into a 'sleeping death'), the child eats the apple.  This child clearly had suicidal intent, but was not likely to die from eating an apple.

All of the phrases I outlined in my first paragraph above have entirely different meanings, even though they are commonly used in place of one another.  It is very important to understand the difference between these phrases. 

Aislinne, you might take a look at the S-STS (both the standard and the Clinically Meaningful Change Measure versions) to see if it adequately meets your needs in evaluating suicidal intent.

In addition to the S-STS, you might consider looking at the suicidal intent questions on the Suicide Plan Tracking Scale (SPTS).  The SPTS also contains  sections on suicidal intent in both the main scale and in the Optional Items pages of the scale. (See second link below.) 

I can send anyone interested the paper mentioned above (which contains copies of the S-STS) or a copy of the SPTS, just send a request.

Article Status Update on the Sheehan-Suicidality Tracking Scale (S-STS) 2014

Technical Report Suicide Plan Tracking Scale (SPTS)

Responses to this question have nicely illustrated the difficulty and complexity of adequately assessing suicide risk and predicting suicidal behavior. The Adult Suicidal Ideation Questionnaire (Reynolds, 1991b) has demonstrated predictive validity for suicide attempts during a 3 month follow-up among inpatients who had made a previous attempt (Osman et al., 1999). [The military suicide research consortium has a brief reviewer of risk assessment measures here.] However, no single assessment measure or structured clinical interview has the capacity to adequately predict who will attempt suicide. False positives are certainly a problem. However, suicide risk assessment and management is still vital to patient safety. Hopefully some day we will have a validated assessment battery (including objective measures that aren't reliant on self-report) to more directly guide clinical decision making. In the mean time here are some useful references (both clinically and from a medicolegal perspective) for considering relevant variables and assessing risk:

Homaifar, B., Matarazzo, B., Wortzel. H.S. (2013). Therapeutic Risk Management of the Suicidal Patient: Augmenting Clinical Suicide Risk Assessment with Structured Instruments. Journal of Psychiatric Practice, 19(5), 406-409.

Wortzel, H.S., Matarazzo, B., Homaifar, B., Brenner, L.A. (2014). Therapeutic risk management of the suicidal patient: Stratifying risk in terms of severity and temporality. Journal of Psychiatric Practice, 20(1), 63-67.

Matarazzo, B.B., Homaifar, B.Y., Wortzel, H.S.  (2014). Therapeutic risk management of the suicidal patient: Safety planning. Journal of Psychiatric Practice, 29(3): 220-224.

The Rocky Mountain MIRECC also has several archived presentations on suicide risk assessment that are relevant for both Veterans and civilians:

http://www.mirecc.va.gov/visn19/education/presentations.asp

https://msrc.fsu.edu/sites/msrc.fsu.edu/files//MSRC%20Screening%20Measures%20White%20paper%20June%202012.pdf

http://www.mirecc.va.gov/visn19/education/presentations.asp

Measuring suicidal intent after a suicide attempt, is not too difficult, I think. Tbe Beck Scale is pretty good and I don't now of any better one. When I used it some years ago,on a very large sample of attempters, I decided to concentrate on its first part (Circumstances of the Attempt) rather than on the second (Self-Report) , on the grounds that self reports of feelings -compared to actions- are less objective or reliable and more difficult to interpret.

But there is no need to despair! There are no perfect "measures" of things in psychiatry and as far as estimating "risks" meaninfuly the choice is roughly between some bad and some not so bad estimates of suicide risk. For a brief discussion of these issues see my paper on Clinical Problems in Assessing Suicide Risk  (in Suicide: Biopsycological Approaches, Botsis et al, Elsevier Science, pp 167-175).

Finally, don't forget that although "intent" can be serious enough to kill you, it simply refers to a state of mind which is present for an instant. So, when you measure a person's intent, you are in no position to know if such intances will be experienced, by the same person, ever again and most importantly "when?". Therefore, the important thing for you is how to plan you study sensibly in order  to show a meaninful result!  Wishing you the best of luck.  

Dear Aislinne, this is an excellent question. It has been addressed in several studies, but there is still a good deal of confusion around many evaluation factors. If you want to evaluate the degree of intent to die of a past suicide attempt, Beck's measure is both excellent and poor at that. It contains some of the best items, on wish to die, availability of rescue, etc. It also includes some items that have demonstrated poor ability to predict current or future suicidality/risk such as writing suicide notes or other communications.

Predicting future suicidality is extremely difficult, as Jennifer and others state. However, any decent measure should be unidimensional (covering only suicidality) and should include items on suicidal affect (e.g., wish to die), behaviors (e.g.,. past attempts modified by intent to die), and cognition (e.g., suicidal thoughts). We tested and verified these ABCs in our scale development paper. We also found serious limitations in other measures, such as those mentioned above. Most include items that are not on suicide (e.g., risk-taking, non-suicidal self-harm) and/or use dichotomous items etc.

The Hjelmeland et al. paper is a bit old but evidence consistently shows that degree of intent to die is very important and should always be included. The Ploderl et al. paper looks into this further. Our paper, the ABCs, provides an example of searching for a more ideal overall test of suicidality.

Article A Closer Look at Self-Reported Suicide Attempts: False Posit...

Article Parasuicide: The value of suicidal intent and various motive...

Article The ABC’s of Suicide Risk Assessment: Applying a Tripartite ...