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Venezuela's entertaining president, Hugo Chavez, was recently reported to have speculated that the USA has developed a secret technology to give cancer to left-wing leaders in Latin America.

I think this claim is a little too crazy to merit skeptical analysis. However, according to the BBC report

he said the instances of cancer among Latin American leaders were "difficult to explain using the law of probabilities".

Now that constitutes a simple claim that does merit some skepticism.

Reworded the question is this: is the incidence of cancer in South American political leaders unusually high? Is the answer different for the subgroup who are left wing in their politics?

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7  
4 data points does not a conclusion make –  ratchet freak Dec 31 '11 at 14:55
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XKCD should do a survival curve of Latin American leaders! –  Andrew Grimm Jan 1 '12 at 8:09
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Define left-wing, define leader. –  user unknown Jan 2 '12 at 5:18
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It seems that unless the cancer is actually manifesting as a ball of lead traveling 500 miles an hours that cancer is not the preferred method of assassination for South American(or any American) leaders. –  Chad Jan 3 '12 at 14:19
    
@Chad: 500 mph? That'd be rather slow, even for a pistol bullet, not to mention rifle. –  vartec Dec 12 '12 at 10:58
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2 Answers

up vote 24 down vote accepted

There are 20 countries in Latin America1, of which 5 have had cases of leaders with cancer (one country, Brasil, had two cases). This equates to 6 in 20 cases, or ~33% incidence of the disease. Note that the original article does not include Fidel Castro in the list of cancer victims, I did.

Is this figure "difficult to explain using the law of probabilities"?

The average incidence of cancer2 is ~41% (counting both genders). So, no, it's not really surprising. Actually, it's even a bit low according to statistics.

It seems to me that Chavez is actually an unintentional victim of the fallacy of cherry picking3:

Cherry picking, suppressing evidence, or the fallacy of incomplete evidence is the act of pointing to individual cases or data that seem to confirm a particular position, while ignoring a significant portion of related cases or data that may contradict that position. It is a kind of fallacy of selective attention, the most common example of which is the confirmation bias. Cherry picking may be committed unintentionally.


1 See "Latin America".

2 See "Lifetime Risk of Developing or Dying From Cancer".

3 See "Cherry picking (fallacy)".

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I like the answer. Only improvement would be to quote the stats over a defined period not just at a point in time and/or to weight by political inclination. –  matt_black Jan 1 '12 at 23:19
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If Brazil had two cases, then the population isn't 'one leader from each country' but some other, larger, definition, which makes the incidence rate potentially even lower! –  Oddthinking Jan 1 '12 at 23:21
    
Oops on my part as I've just noticed the disjunction between the headline and the text: latin america isn't south america. So the castro brothers are excluded from this answer. @sklivvz I don't want to ruin the answer by editing the headline: any suggestions? –  matt_black Jan 3 '12 at 0:24
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Country leaders tend to be rich. I am guessing that the 41% does not spread evenly among all levels of fortune. –  anonymous Jan 4 '12 at 8:38
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@anonymous maybe, but keep in mind that this is the incidence and not the mortality (i.e. who gets a cancer, not who dies from it) :-) –  Sklivvz Jan 4 '12 at 8:59
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The point made by Hugo Chávez is not that a disproportionate number of current Latin American heads of government have developed cancer in their lifetime.

What he actually meant is that the number of prominent Latin American leaders who have been in political conflict with the governments of the United States in the latest years have developed cancer in the latest years unusually often.

The alleged cancer "epidemic" has apparently started with Fidel Castro in 2006. The time interval to take into account is 2006 to 2011.

Let's list the Latin American countries with a left-leaning anti-US government that took part in the ALBA alliance promoted by Chávez and Castro:

  • Venezuela, led by Hugo Chávez.
  • Cuba, led by Fidel Castro, then Raúl Castro.
  • Ecuador, led by Rafael Correa.
  • Nicaragua, led by Daniel Ortega.
  • Bolivia, led by Evo Morales.
  • Honduras, led by Manuel Zelaya, then overthrown by a pro-US coup.
  • Dominica, led by Roosevelt Skerrit.
  • San Vicente and the Granadines, led by Ralph Gonsalves.
  • Antigua and Barbuda, led by Baldwin Spencer.

Beside the ALBA countries, it makes sense to add the following South American governments who are unanimously regarded as friendly towards the ALBA and somewhat conflictual with the United States:

  • Brazil, led by Lula Da Silva, then Dilma Rousseff.
  • Argentina, led by Nestor Kirchner, then Cristina Kirchner.
  • Paraguay, led by Fernando Lugo.
  • Uruguay, led by José Mujica.

We have 16 candidates for the "cancer attack". 6 of them (Chávez, Fidel Castro, Lula, Roussef, Cristina Kirchner, Lugo) were diagnosed with cancer in the time interval. One of them died of heart failure, another one was removed with a coup.

Birth year of the people mentioned above:

  • Fidel Castro 1926.
  • Raúl Castro 1931.
  • Mujica 1935.
  • Ortega 1945.
  • Lula 1945.
  • Gonsalves 1946.
  • Rousseff 1947.
  • Spencer 1948.
  • Nestor Kirchner 1950.
  • Lugo 1951.
  • Zelaya 1952.
  • Christina Kirchner 1953.
  • Chávez 1954.
  • Morales 1959.
  • Correa 1963.
  • Skerrit 1972.

The males had an average age of 58 in 2006, the two women of 56. We can find out the incidence rate of cancer for US residents that age and sex at http://seer.cancer.gov/faststats/selections.php, which should give a hint at the typical values. The latest data (2008) give an yearly incidence rate lower than 1% for males, lower than 0.8% for females. Since we are talking about 6 years (2006 to 2011), this means that less than 6% of men that age and less than 5% of women that age are expected to be diagnosed with cancer. In this sample, it happened to 29% of males and 100% of females. The sample is very small but the mismatch with the usual values is very high.

It sounds like Chávez's suspicion is not entirely lacking grounds.

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4  
(a) Your selection of "victims" is biased because you have not specified an objective criteria. (b) If you get the combined stats from cancer.gov for male and female, you get 1.45% per year. (c) The selection of years is skewed, because it starts with a cancer. You can't simply ignore the years with no cancer. –  Sklivvz Jan 5 '12 at 15:11
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All in all, your answer may be representative of what Chavez meant, but certainly it also shows the same cherry-picking. –  Sklivvz Jan 5 '12 at 15:12
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(a) The criterion is qualitative, of course. The ALBA is notoriously antagonistic towards free-trade treaties promoted by the US government. Brazil, Argentine and Paraguay have all established strong diplomatic and political links with this group of countries, while other countries like Colombia or Panama or Mexico have not. If there is a country-government that you would include in the list or exclude from it, please tell me. Clearly, we cannot comment on a Latin American political issue without a knowledge of Latin American politics. –  Mauro Vanetti Jan 5 '12 at 15:39
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(b) You have done males+females 50+ (why?), I have separated males and females and taken 50-64 (only the Castros were older than 65 in 2006). In any case, even by using your pick, you get an expected incidence along 6 years lower than 9%, while the incidence on the full sample (males and females) is 47%. Precisely because my comment was not cherry-picking, even if you make weaker assumptions the outcome does not change much. –  Mauro Vanetti Jan 5 '12 at 15:48
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(c) The point made by the Venezuelan President was the subject of this debate, and he clearly meant that. You could extend the time range back to 2001, when the sharpest conflicts with the Venezuelan government started, and you would still get an unusually high rate of cancers among US opponents in power in Latin America. This does not prove anything, of course, but it explains why Chávez made such an apparently "crazy" remark. –  Mauro Vanetti Jan 5 '12 at 15:51
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