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Astute readers who are still following this series have no doubt noticed that our ‘week(ish)’ has reached its 10th day. Since examining underlying assumptions is a crucial component of critical thinking, we have decided to challenge our readers’ concept of what a week is.

Of course, seven days is the current conventional designation for the length of a week, but there is no physical basis for this unit, unlike the day (Earth’s rotation), or year (Earth’s revolution around the Sun). Indeed, ancient civilizations had a variety of week-lengths: The Egyptians used 10 days, the Etruscans eight, while the Babylonians decided on seven weekdays that they named for the Sun, the Moon, Mercury, Venus, Mars, Jupiter, and Saturn (names that much of the world still uses today). Though it is an inconvenient fact that the timing of the day, lunar month, and year cannot be described with round numbers or simple mathematical relationships, the seven-day week at least had the advantage of (almost) being a quarter of the 27.3-day lunar cycle. 

A more recent suggestion was the French Republican Calendar, established in 1793. The intention was to replace the religious names and connotations of the Gregorian calendar with a secular, scientific, and rational system. This calendar had 30-day months, divided into three weeks with ten days: primidi, duodi, tridi, quartidi, quintidi, sextidi, septidi, octidi, nonidi, décadi. This calendar was abandoned by Napoleon in 1806. Most of the world has adopted the metric system of measurement (which also came out of the French Revolution), but there has been no appetite for implementing a similar reform to our calendar standards.

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Discussion:

Why do we (still) have the seven-day week? Is it worth the effort to try to get rid of it? 

Part 6 of the 2025 Critical Thinking Week Series

There may be no other human construct quite like statistics. In a stroke of a pen or click-clack of a keyboard, something can be created that looks and acts like a statistic. However, for most of us, our understanding of the study of statistics is only a tiny fraction of that of a statistician. This is true regardless of the depth of our knowledge, and regardless of whether the statistic is a complete fabrication or a highly accurate, reliable, and valid report. 

Validity: Does the experiment measure what it is supposed to measure?

Reliability: Are the results consistent and replicable?

Accuracy: Are the measurements true?

Even when data is highly reliable, accurate, and valid, statistics can be used to mislead the user. 

Correlation does not imply causation: Most people have heard the term “correlation does not imply causation” and yet continue to confound the two terms. For example, 100 percent of people who drink milk die. More seriously, however, is the erroneous belief that vaccines cause autism. Because autism is diagnosed at approximately the same time that childhood vaccines are given, people make the connection and assume causation. However, since until recently, almost every child was vaccinated. It stands to reason that almost every child who gets autism was vaccinated, but there is no increase in the rate of autism between the vaccinated and unvaccinated children.

For other wildly amusing examples of non-causal correlations, see Spurious Correlations.

Meaning of statistics: Before declaring statistics to be useful, it is important to also consider what they actually mean. Think of the following claims:

• “We’ll help you save 20 percent more than the competition.”
• “Drug X will reduce your risk of heart attack and stroke by 50 percent more than Drug Y.”
• “Drug A will increase your risk of an adverse event by 5 percent compared to Drug B.”

There is missing critical information in interpreting these claims. 

• Baseline information: What is the baseline for the decreases and increases? If you have a 1 in 1000 chance of suffering a heart attack (0.01 percent chance) and a drug will reduce the risk by 50 percent, you will now have a 0.005 percent chance. The 50 percent reduction is real, but is not significant to most people. In contrast, if you have a 1-in-2 chance of suffering a heart attack, this claim means that your risk is reduced from 50 percent to 25 percent.

In other words:

• Drug X may be reducing the risk of heart attack and stroke from 75 percent this year to 25 percent, if you’re looking at an absolute risk reduction of 50 percent. But more likely, someone’s risk of heart attack and stroke is being reduced from two percent to one percent, which is also a 50 percent decrease, but only relatively better. 
• Drug A may increase the risk of an adverse event from 10 percent to 15 percent, a 5 percent absolute increase. But more likely, someone’s risk is increasing relatively from 10 percent to 10.5 percent, a 5 percent relative increase.

This is how marketing works. It takes advantage of our reliance upon, and widespread inability to properly interpret, statistics. But it isn’t just those driven by the Friedman Doctrine who misuse statistics. We must hold ourselves and those we trust to the standard of properly representing statistics. Demand of everyone, everywhere, and every time that the baseline rates and probabilities, and whether relative or absolute differences, are being reported.

For more information: See CFIC’s 2010 presentation, “The Curious World of Probabilities with Professor Jeffrey Rosenthal.”

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Discussion:

What statistics have you relied on and later learned were faulty? What are other ways that statistics can be misleading?

Much of the strife in the world today boils down to people having, and sharing, unshakeable thoughts and ideas. Conversation becomes a battle to prove oneself right and others wrong. Many otherwise critical thinkers are of the opinion that if everyone thought critically about the same thing, they would each come to the same (correct) conclusion. This belief ignores the fact that each of us perceives “correctness” based on what we value.

For example, when choosing good economic policy, are we seeking the economic policy that benefits us personally, the one that is good for the geographic area we live in, or the one that spreads the wealth broadly and fairly around the world? When contemplating good healthcare spending, do we value saving lives, minimizing infirmity, or increasing life expectancy?

Critical thinking includes being open to hearing others’ ideas and striving to understand their perspectives. A good conversation that seeks to understand rather than change minds is the key to good critical thinking. Provided both parties agree that it’s OK to believe (and value) different things, people with contrary opinions can have good conversations and remain friends. The Conversation offers some great tips on improving conversation when we disagree. 

All ideas grow out of other ideas. —Anish Kapoor

If your dignity hinges upon your (perceived) intelligence, it may often be tempting to believe that you are right and everyone else is either misinformed or unintelligent. Critical thinkers must avoid this temptation. In fact, even among very learned people, there are differences of opinion. Sometimes there is no “right” solution, only a better solution for your value system. Learning to disagree without being disagreeable (or judgemental) — the humility in seeing the validity of diverse conclusions — is the key to a more civil and democratic society.

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Discussion:

What have you learned from someone with a different perspective? Did it change your perspective?

Humans are no strangers to taking shortcuts. One type of these shortcuts, heuristics, helps us to make quick decisions, based on prior experience and pattern recognition, creating “rules to live by.” 

Historically, we have survived as a species by associating stimuli with action. For example, associating noise from a nearby bush with a threat and taking quick action without thought may help you avoid being eaten. “Avoid potential danger” is not usually a bad idea: Better to act without needing to, than to wait to find out. These quick thoughts free up cognitive capacity, but they also make our decisions prone to biases. Our biases are based on previous experience, values, and beliefs and are often unconscious. Biases may be helpful (like avoiding becoming dinner for a predator) or harmful (such as vaccine hesitancy), and they affect how we see the world and the decisions we make. And, everyone has them. 

By recognizing and understanding our biases, we can make better decisions. One place you can learn about biases and think about which affect you is the Centre for Evidence-Based Medicine’s Catalogue of Bias. 

Sometimes we overemphasize information that comes from a specific source or that fits with an internal paradigm. One way to begin to understand the values that make you hold on to biases is by taking Clearer Thinking’s Intrinsic Values Test (note that you will need to provide an email address to receive the full report from this test).

Our values may cause us to hear only the ideas that match our preconceived ideas and are unable to hear or interpret anything that is contrary. In its extreme, this leads to anti-vax thinking, flat-Earth beliefs, racism, and a host of other dangerous campaigns.

To improve our thinking processes, we need to identify and be willing to adjust for our biases and values.

For more information about how our values and biases cause us to think illogically, see the Podcast for Inquiry episode, Science Denial: Why it Happens and What To Do About It, with Gale Sinatra.

Discussion:

What are the values and biases that you hold? Have you ever engaged in a conversation with someone where they (or you) were unable to overcome biases?

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These days, it seems trivially obvious that it is impossible for one person to know everything. Arguably, this was not the case in the past: Some have said that the philosopher Aristotle knew all that there was to know at the time (though in retrospect, a lot of it was incorrect). Others have identified the brilliant 17th century polymath Athanasius Kircher as the “last man to know everything.” But in any case, in this millennium, we need to acknowledge that we will all need to rely on others for expertise on at least some topics.

The challenge is knowing how to identify which experts to trust. Expertise is acquired from academic learning, hands-on experience, self-study, or a combination of all of these.

For science topics, the “gold standard” for an expert is to have academic qualifications in the field; even better if they are publicly recognized for their expertise, and/or have published papers in high-quality journals. Of course, scientific papers are usually highly technical and challenging for people outside the field. Enter the “science communicators” who help to cut through the jargon and provide explanations accessible to the general public. Many are knowledgeable and trustworthy; some are even scientists themselves, but if and when they are speaking outside their own area of expertise, some extra scrutiny is indicated.

But often, we also want to deploy our critical thinking skills in areas outside of science — practical matters like fixing cars or building furniture. In that case, the criteria for expertise are more likely to be based on practical experience (which may or may not be built on or scaffolded by formal academic education or training).

Some fields, such as medicine or engineering, depend on practical applications of scientific principles. In these areas, experts must be able to demonstrate a combination of academic education and practical experience.

Cautionary notes about “expertise”:

• Some “experts” use academic qualifications in one field to sound credible in another; for example, a computer scientist who pontificates on vaccinations.
• Some journals present themselves as scientific, but articles are not peer-reviewed, and often authors pay to publish their non-peer-reviewed (low quality) work.
• Some “experts” use their expertise for personal gain. Their information may or may not be accurate. If the expert has an ulterior motive for their claims, it is important to give their claim more scrutiny.
• Not all academic qualifications are equal. Experts should be vetted by ensuring that the institution they are citing is accredited and to ensure that they are being truthful about their affiliation with that institution. 
• There are better and poorer practitioners in every field and the esteem of peers is often a good indicator of qualifications. Peer recognition can take the form of publications (as discussed above), as well as memberships/accreditation from governing bodies, such as professional associations, and government licensing boards. (Additional scrutiny may be required to validate these credentials, especially in the case of self-governing organizations; for example, homeopaths in Ontario are legally required to be registered with The College of Homeopaths of Ontario, but that organization explicitly states that it “does not have a role in advocating for or against the efficiency of homeopathy.”)

In some cases, evaluating expertise can literally be a matter of life or death. Many people look to the internet for information regarding medical concerns. There is a wealth of information available from hospitals, medical schools, and health-related non-profit organizations. Again, the validity of the information provided by organizations depends on the credentials of the contributors and compilers. As with individuals, organizations may have ulterior motives, or they may fail to carefully vet their contributors. Recently, questions have been raised about the increasing tendency to provide information generated by artificial intelligence Large Language Models, despite the risk of insertion of information generated by the LLM’s hallucinations or confabulations.

In summary, experts (whether individuals or organizations):

• have formal qualifications, and/or a “track record” of accuracy and credibility,
• are willing to acknowledge when they are wrong,
• do not claim that their expertise in one area gives them the ability or credibility to speak on anything that is outside their field, and
• freely admit that they have their own biases, and disclose their potential conflicts of interest. 

For more on who (and how) to trust, check out the Podcast for Inquiry episode The Search for Truth, with Carolyn Biltoft.

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