Hickam’s Dictum: Definition, Examples & Occam’s Razor

Updated October 2026 · reviewed for today

In short

Hickam’s dictum is a medical counterweight to Occam’s razor: a patient’s symptoms may come from several diseases at once, so the simplest single explanation is not always the right one. It is usually quoted as “patients can have as many diseases as they damn well please” and is attributed to John Hickam (1914-1970), an American physician who chaired the department of medicine at Indiana University.

Table of Contents

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How it works

01

Find the main explanation

Start with the diagnosis or cause that best explains the core problem.

02

Check what is left over

List the findings the main explanation does not account for.

03

Sort the extras

Ask whether each extra is linked to the main cause, already known, an incidental finding, or a separate problem.

04

Act on each real cause

Treat or fix each cause that actually contributes, not only the first one found.

Where you see it today

Multimorbidity is common

In data on 1.75 million patients in Scotland as of March 2007, 23.2% had two or more long-term conditions, and more people under 65 than over 65 had them (Barnett et al., 2012, The Lancet). The authors argued that health care built around single diseases does not fit this reality.

Testing the dictum

A review of 83 published case reports (Aberegg, Poole and Locke, 2024) found that most second diagnoses were causally linked to the first, incidental findings or known existing diseases; a truly unrelated second disease was rare. Their framework reconciles Hickam with Occam rather than choosing one.

AI and the differential diagnosis

AMIE, a language model built for diagnostic reasoning, was tested on 302 difficult published cases; clinicians helped by it produced more complete lists of possible diagnoses than those without it (McDuff et al., 2025, Nature). Broad lists are where Hickam’s caution matters.

Diagnosing business problems

When an AI rollout disappoints, it is tempting to blame one thing: the model. Often the data, the workflow, the incentives and the training are all part of it, and fixing only one leaves the rest in place.

Hickam's dictum and related ideas

Hickam's dictum

Rule of thumbSeveral causes may coexist

Risk if misusedChasing every minor finding

Occam's razor

Rule of thumbPrefer the simplest explanation

Risk if misusedStopping at the first neat answer

Root cause analysis

Rule of thumbTrace a problem back to its source

Risk if misusedAssuming there is only one root

Base rate fallacy

Rule of thumbIgnoring how common things are

Risk if misusedOverrating rare diagnoses or causes

Second-order thinking

Rule of thumbAsk what follows from the first effect

Risk if misusedOvercomplicating simple cases

How to use it

• Start with the simplest explanation, then list everything it fails to explain.
• Classify leftover findings: linked, pre-existing, incidental or truly separate.
• In post-mortems, ask “what else contributed?” before closing.
• When an AI project underperforms, review data, model, workflow and incentives separately.
• Use AI tools to widen the list of possible causes, then check each one against evidence.

The Business Engineer lens

AI projects rarely fail for one reason; they fail where data, models, processes and incentives meet. The Business Engineer argues for this kind of system thinking, looking at the whole set of causes rather than the single most visible one.

Read: AI & The Importance of System Thinking →Explore the platform →

Related: Occam's razor · Root cause analysis · First principles thinking · Second-order thinking · Base rate fallacy

Frequently asked questions

What is Hickam's dictum?

It is the principle that a patient can have several diseases at once, so symptoms do not always have a single explanation.

Who was Hickam?

The dictum is attributed to John Hickam (1914-1970), an American physician who chaired the department of medicine at Indiana University.

How is Hickam's dictum different from Occam's razor?

Occam's razor favours the simplest single explanation; Hickam's dictum warns that several causes may be present at once.

How does Hickam's dictum apply to business?

It reminds managers that a disappointing result, such as a stalled AI rollout, may have several causes at once, each needing its own fix.

Sources

• Radiopaedia, Hickam's dictum
• Aberegg, Poole & Locke (2024), Hickam's dictum: an analysis of multiple diagnoses, Journal of General Internal Medicine
• Barnett et al. (2012), Epidemiology of multimorbidity and implications for health care, research, and medical education, The Lancet
• McDuff et al. (2025), Towards accurate differential diagnosis with large language models, Nature

The full guide

The complete explainer, cleaned up and reformatted for mobile.

Hickam’s dictum is the counterargument to Occam’s razor. Whereas Occam’s razor is a heuristic that tends to narrow down decision-making to the simplest variables, Hickam’s dictum believes a situation must be tackled by looking at multiple variables.

Understanding the Hickam’s dictum

Occam’s razor is used in the medical industry to imply that multiple symptoms in a patient can be attributed to a single disease.

Hickam’s dictum counters this argument, believing the patient’s multiple symptoms to be, in most cases, the result of several diseases.

Hickam’s dictum is based on an aphorism usually stated as “patients can have as many diseases as they damn well please.”

This line is attributed to John Hickam, an American physician who worked at Grady Memorial Hospital in Atlanta in his early career and then became chairman of medicine at Indiana University between 1958 and 1970.

Hickham’s dictum and diagnostic parsimony

In contemporary medicine, Occam’s razor is often discussed by doctors in the context of diagnostic parsimony.

This principle advocates that doctors look for the fewest possible causes to account for all symptoms when diagnosing an injury, illness, or disease. 

This approach has limited use in modern medical practice, however, with the actual process of patient diagnosis consisting of multiple hypotheses that must be tested and modified as necessary.

Hickam’s dictum asserts that as doctors carry out this process, no potential diagnosis should be excluded on the basis that it does not appear to satisfy the principle of Occam’s razor. 

Note that Occam’s razor does not require that the doctor necessarily choose the simplest diagnosis.

Instead, it encourages the practitioner to find an explanation that accounts for all evidence without making undue assumptions.

With the above in mind, Occam’s razor can be a useful diagnostic tool – but it is by no means infallible. In medicine, the simplest answer – or the one with the fewest number of diagnoses – is not always the correct answer. 

Hickam’s dictum and statistical analysis

That Hickam’s dictum can serve as a counterargument to Occam’s razor is down to statistical analysis.

Stats show that patients are more likely to have multiple diseases and less likely to have one, rarer disease that accounts for all their symptoms. 

Some patients with multiple diseases may also receive a diagnosis that each disease has an independent cause rather than all diseases being attributable to a single source.

That is, each disease is derived from separate events (or a combination of events) to which the patient has been exposed. 

When doctors diagnose a patient with one rare disease, they make a critical assumption that is often unrelated to the patient’s symptoms and is statistically unlikely in any case.

Conversely, when the patient is diagnosed with three common conditions to which they may already be predisposed, the doctor minimizes the introduction of new assumptions that can lead to an incorrect diagnosis.

Relevance in Healthcare

Hickam’s Dictum is highly relevant in healthcare settings, especially in clinical practice and medical decision-making:

1. Complex Patients: In modern medicine, patients often have comorbidities or overlapping symptoms that require careful consideration and a comprehensive diagnostic approach.
2. Avoiding Misdiagnosis: The principle helps prevent the misdiagnosis of patients who may have multiple medical conditions, ensuring they receive appropriate treatment.
3. Diagnostic Challenges: In cases where symptoms are not typical or do not fit a single diagnostic pattern, Hickam’s Dictum encourages healthcare providers to explore a broader range of possibilities.
4. Holistic Care: It promotes a holistic approach to patient care, taking into account the diverse factors that may contribute to a patient’s health.

Impact on Medical Decision-Making

Hickam's Dictum has several implications for medical decision-making

1. Broad Differential Diagnosis: Healthcare providers should maintain a broad differential diagnosis, considering multiple potential conditions when evaluating a patient.
2. Thorough Evaluation: Patients with complex presentations may require more extensive diagnostic testing and evaluation to identify all relevant conditions.
3. Collaboration: Interdisciplinary collaboration among healthcare professionals is essential to ensure all possible conditions are considered and evaluated.
4. Individualized Treatment: Recognizing multiple coexisting conditions allows for individualized treatment plans that address the specific needs of each patient.

Potential Implications for Patient Care

Adhering to Hickam’s Dictum can lead to several positive implications for patient care:

1. Accurate Diagnosis: Patients are more likely to receive accurate and timely diagnoses, leading to appropriate treatment.
2. Improved Outcomes: Addressing all relevant medical conditions can lead to better patient outcomes and overall health.
3. Patient Satisfaction: Patients may experience increased satisfaction with their healthcare when their concerns and symptoms are thoroughly evaluated and addressed.
4. Preventing Harm: Avoiding misdiagnosis or underdiagnosis of serious conditions helps prevent patient harm.

Hickam’s dictum in business

As the volume, variety, and velocity of modern datasets increases, the probability that a business will encounter Hickam’s dictum increases in turn.

Data can now be combined to diagnose and solve problems in a way that was once unimaginable, so the relative simplicity of Occam’s razor may be less useful in some instances.

With that said, most businesses will benefit from a combination of advanced data analytics (Hickam’s dictum) and Occam’s razor where they default to the simplest explanation possible.

McDonald’s

Take McDonald’s, for example, where almost every process has been recorded and standardized to increase efficiency and profits.

In fact, the company is a master of solving problems with simple solutions and then turning them into systems. 

Many restaurants contend with the problem of sourcing trained cooks and chefs, but McDonald’s solves this issue with simple menu items that can be quickly and easily prepared by anyone.

Indeed, the company could take a high school student off the street with zero experience and teach them to prepare a Big Mac in a matter of days. 

There are also systems in place to ensure the food is made to a consistent standard, such as those that dictate the correct temperature of the fryer.

The bathrooms in McDonald’s restaurants are also clean and functional and its systemized employee training program is respected around the world.

McDonald’s and data

While McDonald’s is a systemized company, it is not afraid to make decisions and solve problems based on data collected from its vast network of restaurants. Based on this data, for example, the company identified three areas of improvement:

1. The design of the drive-thru itself.
2. The information provided to customers in the drive-thru, and
3. The nature of the people waiting in line to order. 

By analyzing the data, McDonald’s was able to determine what times of day customers were most likely to visit and add extra staff to reduce wait times.

But it has also introduced AI that analyzes local buying patterns based on factors such as events, celebrations, weekends, or even whether it is payday for employees in the area.

Based on these patterns, the AI recommends relevant food and drink suggestions on the drive-thru screen for that specific restaurant and time of day.

The point is there that to improve its drive-thru experience, McDonald’s did not default to the simplest or most likely solution (reducing wait times).

Instead, by analyzing data from its restaurants, the company determined that its inadequate drive-thru experience could be explained by multiple, less-common “diagnoses” that may have otherwise been overlooked.

Key takeaways

• Hickam’s dictum, used in the medical industry as a counterargument to Occam’s razor, believes multiple symptoms can be attributed to one disease.
• In contemporary medicine, Occam’s razor is often discussed by doctors in the context of diagnostic parsimony. This principle advocates that doctors look for the fewest possible causes to account for all symptoms when diagnosing an injury, illness, or disease. 
• Hickam’s dictum is a counterargument to Occam’s razor because it is based on statistical evidence. Stats show that patients are more likely to have multiple diseases or comorbidities and less likely to have one, rarer disease that accounts for all their symptoms.

Key Highlights

• Introduction to Hickam’s Dictum: Hickam’s Dictum serves as a counterargument to Occam’s Razor. While Occam’s Razor simplifies decision-making by considering the simplest variables, Hickam’s Dictum suggests that situations should be analyzed by considering multiple variables.
• Application in Medicine:
  • Occam’s Razor is often used in medicine to attribute multiple symptoms to a single disease.
  • Hickam’s Dictum counters this, asserting that patients can have multiple diseases causing their symptoms, rather than a single disease.
• John Hickam and the Dictum:
  • John Hickam, an American physician, is attributed to the phrase “patients can have as many diseases as they damn well please,” forming the basis of Hickam’s Dictum.
• Hickam’s Dictum and Diagnostic Parsimony:
  • Diagnostic parsimony involves seeking the fewest possible causes for all symptoms in medical diagnosis.
  • Hickam’s Dictum asserts that the process of diagnosis involves testing and modifying multiple hypotheses, without excluding potential diagnoses based on Occam’s Razor.
• Counterargument in Medical Context:
  • Occam’s Razor encourages finding explanations that account for evidence without assumptions.
  • Hickam’s Dictum recognizes that the simplest explanation might not always be the correct one, and multiple diseases could contribute to symptoms.
• Hickam’s Dictum in Statistical Analysis:
  • Statistical analysis supports Hickam’s Dictum, indicating patients are more likely to have multiple diseases than a single rare disease accounting for all symptoms.
  • Some patients might have comorbidities with independent causes for each disease, rather than a single source.
• Application in Business and Data Analysis:
  • As data complexity increases, Hickam’s Dictum gains relevance.
  • Combining advanced data analytics with Occam’s Razor can be beneficial in business problem-solving.
• McDonald’s Example:
  • McDonald’s employs data-driven decision-making alongside its systemized operations.
  • Analyzing data from its restaurants helped McDonald’s identify areas of improvement and tailor its drive-thru experience using AI.
• Key Takeaways:
  • Hickam’s Dictum counters Occam’s Razor by emphasizing the consideration of multiple variables.
  • Medical diagnosis involves diagnostic parsimony and the testing of multiple hypotheses.
  • In business and data analysis, a combination of advanced analytics and simpler explanations can yield effective solutions.