2.7 Mediator variable

It happens that experimental data proves causality between two variables but it does not give insight to understand the relationship. Mediator variable is introduced to split the original relationship into the chain of cause-and-effect links. It allows clarify the nature of the relationships.

It might seem a bit abstract, so let’s proceed with an example.
The Aztecs believed that solar eclipse preceded the apocalypse, so they practiced ritual human sacrifice to appease the gods and save the world. There is an evidence that eclipses led the Aztecs to kill slaves and prisoners. If we could ”generate” more eclipses, we would have observed more massive homicides. Is it fair to say that eclipse caused the massacres? Could a distant neutral cosmic phenomenon cause manslaughter?

The relationship makes more sense if we introduce a mediator variable and realize that it was the Aztecs’ fear and belief system that caused killings. Then we get a chain of two valid causal relationships:

• Solar eclipse caused people’s fear
• People’s fear caused killings

In reasoning, sometimes we need to go deep to find the underlying cause. At times, on the contrary, we must search for the more direct cause. Otherwise, if we trace back the cause-and-effect relationships too far, we will find the cosmological Big Bang to be the cause of all events which is not very helpful.

Identifying mediator variables is important in making rational decisions. Without understanding that human fear is the more direct cause, the hypothetical progressive Aztecs had not been able to make a right conclusion, that in order to prevent eclipse inspired homicide, they needed to educate people and eradicate religion and superstition.

Specific claim

In Italy the new virus caused so many deaths that corpses pile up and must be transported out of the city by the army trucks [34, 47, 38].

Let’s start with a side note that it is an example of our selective attention. The above caption makes such a good news story and the topic for water-cooler gossips, that a few days before it actually happened, a fake news with a similar headline appeared in social media. It was showing the footage of army trucks allegedly transporting the bodies. The news was quickly debunked and
refuted by finding that the video of army trucks had been recorded in a different part of the world.

Nevertheless, the fact is that on March 18th, 2020, there was an isolated incident of using 15 military trucks and 50 soldiers to transport about 60 coffins from Bergamo to remote cremation sites.

The demand for cremation increased. What was the cause? It’s so easy to come to the immediate conclusion that some disastrous plague produced extraordinary death toll. It’s not supported by data, though. As we checked using the z-score data from Euromomo [11], the all-cause mortality in Italy increased in the middle of March, but the increase was comparable to the seasonal flu mortality upsurge in previous years [30, 36, 7]. The caveat is that these are country-wise statistics that may flatten out regional anomalies.

Nevertheless, it is fair to compare, because the previous years seasonal flu outbreaks also had regional character.

For example, in January 2017 the z-ratio increased to 12, the same as in the middle of March 2020. If we assume the most unfavorable delay in reporting we get z-score equal 18 for late weeks of March 2020. For Italy mortality data, z-score 12 corresponds to about 40% increase relative to the yearly average of 12500 deaths / week; z-score 18 corresponds to about 60% increase. It means that in January 2017, Italy had to handle about 17,500 dead per week, and in March 2020 they had to handle 20,000 dead per week [17, 16].

The raw mortality increase does not explain why the crematoria are overwhelmed in 2020 and why they were not three years earlier.
We need to understand the background first and look for the mediator variable then. Cremation in Italy became fully legal and made equal to the burial only in 1987. Such late adoption was the result of the Catholic Church influence that was in strong opposition. Cremation popularity reached 15% in 2012 nationwide, but it is still one of the lowest ratios in Europe.

The numerous reports reveal the following:

1. The government has put a stop to funerals and religious ceremonies. There is no ban on burials, but often there is no such possibility, because many funeral homes have closed for fear of catching the virus by staff. The ones that remain open are no longer able to manage the high demand for the service.

2. Since February 2020 Italian authorities increasingly recommend cremation over burial [6]

3. During the coronavirus crisis, more families are choosing cremation over burial, for fear of catching the virus from the dead.

The initially low cremation popularity in Italy explains the lack of proper infrastructure. There were not enough crematoria to handle the sudden increase in cremation needs. This increase was caused by the government decisions and overall state of fear that changed the behavior of the
relatives.

This example of mediator variable is not all-or-nothing. It does not invalidate the fact that the actual mortality in Italy increased in March 2020 however the increase was not sufficient enough by itself to cause the discussed incident. We had to identify a set of mediator variables to explain why crematoria are overwhelmed and why it required using military to transport coffins.

Specific claim

The new virus caused hospitals overload.

As of March 2020, in many parts of the world hospitals are overwhelmed with patients and suffer from inadequate staffing and supply shortages. The medical staff is extremely tired, working long hours and is struggling to get enough protective equipment.

This dire situation cannot be explained only by the sudden surge in cases of severe pneumonia. By itself, it wouldn’t be enough to put some hospitals to a stress. There are many other factors that contributed.

1. Lower hospitalization thresholds
   In most cases coronavirus infection symptoms are mild. The particular attention to this single illness lowered admission criteria to hospitals in the unprecedented way. Mild cases are also hospitalized.
   Hospital beds are also being used to quarantine healthy people returning from abroad [42, 39].
   Most patients are elderly with multiple underlying conditions. Unless the present-day unhealthy excitement over very common symptoms, these people would be passing away surrounded by families in homes, hospices and elder-care facilities. Now, in the state of unwarranted emergency, they are being pulled out from the nursing homes, hospitalized, treated
   like lepers and die afraid, alone and isolated.
   Over a few weeks, the hospital admission criteria have dramatically changed. It is not directly caused by the new disease, but it is a result of new policies, health organization recommendations and overall public focus and fear.
   Normally the above cases would never consume health care system resources.
2. Medical personnel quitting for fear of infection
   Severely exaggerated mortality rate repeated by health authorities and overall contagious anxiety amplified by the media made many health care workers to quit a job as a way to protect themselves and their families.
   Also with the lockdown, schools and childcare facilities closed, some had no other choice than to quit a job and take care of children themselves.
3. Supply chain of medical equipment disrupted by lockdown.
   Despite the medical supplies being exempted from the government restrictions, the general disruption of transport and logistics caused that they are not reaching hospitals [40, 49, 19].
4. Panic shopping drained the medical supplies
   Declaring a state of emergency led to stocking masks and gloves by citizens. In many cases, health authorities recommended buying face masks and gloves in excess by everyone. It led to depleting supplies and shortage for medical personnel.
5. Harassment of health care workers
   Health care workers who remained at their posts are praised by authorities for their dedication and sacrifice. There is another side to the story though. The same authorities, by overstating the deadliness of the new disease and repeating claims unsupported by evidence, incited panic to the level that citizens worry about coming into contact with health workers and contracting disease. There are reports of discrimination and attacks on medical staff. They are being evicted by landlords, refused rides on buses and dispirited by insults [28, 21, 24, 2, 20, 44].
6. Special safety precautions, the extreme measures that make the simplest things difficult. In particular, medical staff complains about excessive new procedures that were never needed before. Whenever a single coronavirus case is detected the entire hospital ward must be isolated, what disrupts normal operation.
7. Health care workers strikes over hazardous working conditions
   The resulting shortages in protective equipment, the hastily imposed changes in hospital procedures caused strikes by medical staff [4, 8, 50].

All these factors let us better understand what happened.
The media, health organizations and general public fixation on one topic, the resulting insecurity and the aura of looming disaster ensued disproportionate response that disrupts normal operation of hospitals more than the inflow of new patients.

We can see more clearly the mediator variable now.

• Obsessive focus on a single pathogen caused the change of people’s behavior and rules, the overall disruption
• The disruption contributed to health care system overload

Specific claim

The virus caused a disaster in Ecuador, where corpses are lying on the streets and 450 bodies were registered on the waiting list to be removed from the houses [10, 3].

Undoubtedly the situation in Ecuador is critical, but what is the cause?

In statistics, there are a few methods of checking if the hypothetical variable is valid. One of them is to forget about the original cause and test if the last link in the chain makes sense. For the Aztecs reformers, it would be helpful if they hadn’t noticed the eclipse and looked at things happening on Earth as they really were.
Let’s do the same in 2020 and imagine we know nothing about the virus or pandemic. We are looking at Ecuador, the country inhabited by 17 million people with average death rate 5.2/1000 (2020 estimated) which gives 88,400 deaths per year or 242 deaths per day.

Imagine that one day the government decided that non-essential activities are to be stopped, by a decree made public services dysfunctional, introduced the curfew, and made funerals effectively banned. Additionally the government found some reason to incite fear and panic, endorsing alarmist claims about some unfathomable danger, with prime minister advising ”not to have a false sense of security, because everyone can get it” [27] and the president threatening anyone who leaves home with 3 years of jail [25] The police backed his words by arresting over 1,500 people for breaking the curfew and scaring the population to the level that people are afraid to do anything, touch anything, and the last thing they might want to do, handle the bodies of their deceased relatives [9].

This is exactly what happens in Ecuador since March 12th when the government entered the scene with new legislation. What kind of output should we expect two weeks later? How Ecuadorians are supposed to deal with the deceased? What other thing can they do than to leave the coffins in the streets?

The mediator variable here is the government actions which are the real cause of the crisis. If anyone thinks that the cause of actions of Ecuador citizens can be traced back to coronavirus, then rightfully it may also be traced back to solar eclipse or Big Bang.

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