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A comment on No person who was born blind has ever been diagnosed with schizophrenia. Parent comment

Re:No person who was born blind has ever been diagnosed with... by primo4444 on Wednesday February 12, 2020 @08:49AM (#22308759)
No, the .02 is correct. If you ignore the percentages part (since both left and right side use it), you're doing

  0.72 x 0.03, which is indeed 0.02
If you do it as probabilities not expressed as percentages, it's 0.0072 x 0.0003, which is 0.0002, but that's 0.02%
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Re:No person who was born blind has ever been diagnosed with... by rlpb on Wednesday February 12, 2020 @08:57AM (#22308814)
You can't just ignore the percentage signs.

0.72% expressed as a decimal is 0.0072. 0.03% expressed as a decimal is 0.0003. 0.0072 x 0.0003 = 0.000002. Expressed back as a percentage, that's 0.0002%.

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Re:No person who was born blind has ever been diagnosed with... by gus_massa on Wednesday February 12, 2020 @08:58AM (#22308820)
> it's 0.0072 x 0.0003, which is 0.0002, but that's 0.02%

No. 0.0072 x 0.0003 = 0.00000216‬ ~= 0.000002 = 0.0002%

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Re:No person who was born blind has ever been diagnosed with... by primo4444 on Wednesday February 12, 2020 @09:02AM (#22308847)
You're right. Not sure how I fell into that trap so easily.
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Re:No person who was born blind has ever been diagnosed with... by injb on Wednesday February 12, 2020 @09:49AM (#22309193)
I wonder if it's better to treat percentage as a unit or variable. So a-percent x b-percent = c(percent-squared), or c divided by 100 twice.
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Re:No person who was born blind has ever been diagnosed with... by petrogradphilos on Wednesday February 12, 2020 @11:11AM (#22309992)
You could also replace % with 10⁻² and use scientific notation:

      0.72% ⋅ 0.03%
    = 0.72 ⋅ 10⁻² ⋅ 0.03 ⋅ 10⁻²
    = 7.2 ⋅ 10⁻³ ⋅ 3 ⋅ 10⁻⁴
    = 7.2 ⋅ 3 ⋅ 10⁻³ ⋅ 10⁻⁴
    = 21.6 ⋅ 10⁻⁷
    = 2.16 ⋅ 10⁻⁶
    ≈ 2 in 1 million
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Re:No person who was born blind has ever been diagnosed with... by prestonh on Wednesday February 12, 2020 @11:33AM (#22310214)
It's because we usually dont multiply percentages, but instead work with normal decimal figures.
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