Posted in Psychology & Medicine

Availability Cascade

We live in a complicated world that constantly throws complex issues at us. Because it is impossible for one person to be an expert in every field, we have to employ different strategies and tactics to navigate through these issues.

A fascinating way that our brain tries to solve a current issue is the availability cascade. This is a self-reinforcing cycle, where an idea essentially “infects” a group of people, displacing individual thought and opinion and overwhelming critical thinking.

The way this happens was described and modelled by Timur Kuran and Cass Sunstein.

First, a new idea that seems to be a simple and elegant solution or explanation to the current issue starts to gain traction. People easily adopt and embrace this idea because it sounds plausible and because it is easy to process.

Secondly, people who adopt these ideas spread it themselves, making it more available in the social network. Particularly, nowadays we see this in both reported and social media.

Lastly, as the availability increases, more and more people are pulled in and the idea seems more credible, because “everybody” seems to think it. People do less research and have less individual thoughts or opinions about the matter because the group consensus is more appealing or acceptable.

The availability cascade as a platform can be very effective at raising awareness of issues and banding people together to fight a common cause, such as when the AIDS epidemic was starting.
However, it is fraught with issues.

The availability cascade is mediated by a heuristic, which is essentially a mental shortcut. Heuristics are extremely useful in that it reduces our cognitive load and automates many of our decisions. However, because they are based on rule sets, they are not as effective for new, different situations.

We are less likely to think critically when using heuristics, meaning that we are more vulnerable to being manipulated. In this situation, people think “this is widely available information, therefore it must be important” and default to believing it (even if it is just to appear “current” and to fit in).

Because critical thinking is overwhelmed by the availability cascade, it can be extremely dangerous when misinformation spreads this way; or worse, disinformation – where people maliciously spread false information for their own gains.

A classic example is the anti-vaccination movement that spawned from a discredited, falsified article that claimed MMR vaccines increased rates of autism, despite mountains of evidence pointing towards the effectiveness and safety of immunisation. Subsequently, vaccination rates dropped and we now see outbreaks of illnesses such as measles, resulting in countless deaths and injuries that could have easily been prevented.

Information can be just as contagious and dangerous as an actual infection. Knowing about the existence of these cognitive biases and phenomena help protect us from falling victim to them.

Posted in Psychology & Medicine


Tetanus is an infectious disease caused by a soil-borne bacteria called Clostridium tetani. Patients are often infected soil entering the blood through deep wounds, such as a cut. The bacteria produces a toxin called tetanospasmin which leads to the characteristic symptoms of tetanus involving muscle.

The term tetanus actually refers to a state where skeletal muscle remains contracted and cannot relax due to maximum signalling from the nervous system. Tetanus is associated with some distinct symptoms involving tetanised muscles.

Tetanus starts in the face in the form of lockjaw (jaw clamps shut and cannot be opened) and sardonic risus sardonicus. Risus sardonicus, also known as sardonic grin, is a contorted, malicious-looking smile that is caused by spasms of muscles in the face. A good portrayal of the grin is seen in the Joker’s face from the Batman comic book series.
The disease then progresses to cause stiff neck, spasming of chest and leg muscles and difficulty swallowing. 

A dramatic symptom is opisthotonos, where the patient experiences extremely painful contractions of back muscles causing them to arch their back against their will. Along with lockjaw and risus sardonicus, it is a characteristic sign of tetanus and has been known for centuries. Before it was attributed to tetanus, people used to think the person was possessed by a demon due to the agonised screams and involuntary spasming of the body.

The disease is especially devastating in infants and can be spread to the fetus within the womb. This is because babies do not have a developed passive immune system that can combat the infection. Neonatal tetanus carries a mortality rate of over 90% and is responsible for 15% of all neonatal deaths.

Tetanus is a preventable disease through immunisation. Immunisation is done by injecting an inactive form of the toxin (i.e. cannot cause disease), inducing a reaction by the immune system. This essentially “teaches” the immune system to defend the body against tetanus. By completing a course of three doses and receiving occasional booster shots throughout life, tetanus can be prevented. Pregnant women must be immunised against tetanus to prevent neonatal tetanus (the babies receive scheduled immunisations soon after birth too).

This is one example of how immunisation can effectively prevent fatal diseases in a population.