Elsevier

Seminars in Oncology

Volume 37, Issue 1, February 2010, Pages 23-26
Seminars in Oncology

Issues related to cancer prediction model
What Is a Real Nomogram?

https://doi.org/10.1053/j.seminoncol.2009.12.003Get rights and content

The current resurgence in the use of nomograms as diagnostic and prognostic tools has legitimate roots in their effectiveness in facilitating communication between the doctor and patient. By returning to a more classical approach to nomography, graphical insights can further enlighten the patient beyond what can be achieved with current methods, while at the same time simplifying the process. We propose a going-forward extension that addresses the issue of further use of computing technology to continue to enhance understanding.

Section snippets

Why Nomograms

A critical issue at the doctor–patient interface is the difference between the doctor “getting an answer” and the doctor explaining it to the patient, both for diagnosis and subsequent treatment alternatives. The distillation of large amounts of historic data can help in predicting the probable outcome for a patient, based on his test results; that part of the problem—getting the answer—is “calculation.” However, in order to make an informed decision, the patient must be comfortable that he

Terminology

Nomography is a technique that has been plagued by difficulties in terminology since its inception over 100 years ago. People have argued whether they should be called “nomographs” or “nomograms,” and the result is that the two terms are perfectly interchangeable today. We will use the term nomogram exclusively. The medical research community has used a specific kind of nomogram, which we refer to as “medical nomograms.” The more general case consists of “classical nomograms,” and we will

Conceptual Computational Framework

Our objective is to distill large amounts of data so that subsequent computations can be done quickly and with as much precision and accuracy as the underlying data permits. Imagine the case of three tests: T1, T2, and T3. A given patient may score S1, S2, and S3, respectively. However, the three tests might not be equally important, with arbitrary weights W1, W2, and W3 for the three tests. If we knew the weights, we could make a prediction of an outcome by computing the weighted scoreO=W1S1+W2

A Medical Nomogram

Figure 1 is a medical nomogram for the computation of a prognosis for prostate cancer patients who have undergone a radical prostatectomy. The objective is to determine the “Trifecta Probability”—the probability that the patient will be free of recurrence, regain continence, and regain sexual function. The authors first rigorously define what they mean for each of these criteria. They then take 6 different factors—PSA, clinical stage, erectile function, biopsy grade, months from the radical

Classical Nomograms

Dr Grimes makes a good point. Strictly speaking, a nomogram enables graphical computation. What is “artificial” in medical nomograms is the need to “graphically” look up points for each factor, then sum them, and then do the “reverse graphical lookup” on the total to achieve the result. A classical nomogram is completely graphical in its execution. However, it is possible to transform the medical nomogram into a classical nomogram. In Figure 2 we present a classical nomogram that encapsulates

Computerized Form Fill-Out

Could the presentation process be computerized? Certainly. A spreadsheet could easily be constructed, or, in some cases, a simple form fill-out could be used to get the answer automatically (eg, www.nomograms.org). This website likely derives its name from its data sources—medical nomograms; however, there are no nomograms of any kind on the site. The advantage of the form fill-out approach is that it uses the same basic information (weights) to do its calculations. The disadvantages are

Comparison of Current Approaches

Dr Grimes believes that, in this day and age, all of these computations should be exclusively done on a personal computer, personal digital assistant, or smartphone, which ironically should make him a fan of www.nomograms.org. We respectfully beg to differ.

All of the computerized approaches suffer from the Black Box effect. On the other hand, the classical nomogram displays the process visually; one can see, for example, that certain factors are less important because their scales are shorter

Recommendation for Future Work

As time marches on, Web access will become omnipresent, so eventually the argument that not everyone has access to computing facilities will lose force. However, we still have the Black Box problem to consider. What would be optimal would be a Web-based tool that would allow us to input the data values and then produce the classical nomogram on the screen. As we varied the input values, the lines would move appropriately. As an example of this approach, see com.pti.website.pages.company.Nomograph

Conclusion

With one simple reformulation, all medical nomograms based on multifactor point summation can be transformed into classical “straight edge” format. The nomogram provides a graphical explanation of a prediction process and can be used where computers cannot. The best future direction is one that combines computerization with classical nomograms.

References (3)

  • J. Eastham et al.

    Predicting an optimal outcome after radical prostatectomy: the “Trifecta” nomogram

    J Urol.

    (2008)
There are more references available in the full text version of this article.

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