Background

Question
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Did Usain Bolt use performance-enhancing drugs? 

Answer
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Usain Bolt did not use any illegal performance-enhancing drugs.

(
96%
probability)

Background
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Since around 2006, Jamaica has supplied many of the world's fastest sprinters. Some have used genetics to explain the Jamaican dominance in sprinting, some credit the Jamaican environment, while others believe that it is the result of rampant cheating in the form of Performance Enhancing Drugs (PEDs). At the center of this debate is Usain Bolt, first recognized when he became the youngest gold medalist ever at the 2002 Junior World Championships. After establishing himself as a professional sprinter, Bolt won 17 of his 18 races between 2007 and 2016, capturing 17 gold medals and setting multiple world records. Since Bolt wins races against athletes known to have taken PEDs, some wonder if Bolt became the world's fastest man by taking PEDs himself.

Hypotheses Considered
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Calculated Results
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Calculated Results
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1

95.9%
Clean:

Usain Bolt did not use any illegal performance-enhancing drugs.

95.9%

2

3.5%
PED as adult:

Usain Bolt started using illegal performance-enhancing drugs after age 15 in 2002, continuing to do so throughout his professional career.

3.5%

3

0.6%
PED since teens:

Usain Bolt started using illegal performance-enhancing drugs before he was 15 in 2002, continuing to do so throughout his professional career.

0.6%

Starting Point
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Initial Probabilities

Name
Initial Likelihoods
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Clean

20%

PED as adult

74%

PED since teens

6%

Name
Initial Likelihoods
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Clean

20%

PED as adult

74%

PED since teens

6%

Evidence
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Effect
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Fast since age 15

Name

Effect

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Updated Likelihoods

Clean
×
10

85%

PED as adult
÷
5

13%

PED since teens
÷
2

2.5%

Bolt has had outstanding performance at the global level since the age of 15. His increased speed falls within the normal range.

Missing evidence: signs of

PED
use.

Name

Effect

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Updated Likelihoods

Clean
×
10

85%

PED as adult
÷
5

13%

PED since teens
÷
2

2.5%

Drug tests

Name

Effect

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Updated Likelihoods

Clean
-

92%

PED as adult
÷
2

7%

PED since teens
÷
2.5

1.1%

Bolt has never failed a drug test and has been vocal against

PED
usage.

Name

Effect

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Updated Likelihoods

Clean
-

92%

PED as adult
÷
2

7%

PED since teens
÷
2.5

1.1%

Physical traits

Name

Effect

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Updated Likelihoods

Clean
×
2

96%

PED as adult
-

3.5%

PED since teens
-

0.6%

Bolt is very tall and his physical record lacks evidence of

PED
usage. 

Name

Effect

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Updated Likelihoods

Clean
×
2

96%

PED as adult
-

3.5%

PED since teens
-

0.6%