**Estimator of True Probability**

The best estimator for the actual value is the estimator .
This estimator has a margin of error (E) where at a particular confidence level. |

Using this approach, to decide the number of times the coin should be tossed, two parameters are required:

- The confidence level which is denoted by confidence interval (Z)
- The maximum (acceptable) error (E)

- The confidence level is denoted by Z and is given by the Z-value of a standard normal distribution. This value can be read off a standard score statistics table for the normal distribution. Some examples are:

Z value | Confidence Level | Comment |
---|---|---|

0.6745 | gives 50.000% level of confidence |
Half |

1.0000 | gives 68.269% level of confidence |
One std dev |

1.6449 | gives 90.000% level of confidence |
"One Nine" |

1.9599 | gives 95.000% level of confidence |
95 percent |

2.0000 | gives 95.450% level of confidence |
Two std dev |

2.5759 | gives 99.000% level of confidence |
"Two Nines" |

3.0000 | gives 99.730% level of confidence |
Three std dev |

3.2905 | gives 99.900% level of confidence |
"Three Nines" |

3.8906 | gives 99.990% level of confidence |
"Four Nines" |

4.0000 | gives 99.993% level of confidence |
Four std dev |

4.4172 | gives 99.999% level of confidence |
"Five Nines" |

- The maximum error (E) is defined by where is the
**estimated probability**of obtaining heads. Note: is the same actual probability (of obtaining heads) as of the previous section in this article.

- In statistics, the estimate of a proportion of a sample (denoted by
*p*) has a standard error (standard deviation of error) given by:

where *n* is the number of trials (which was denoted by *N* in the previous paragraph).

This standard error function of *p* has a maximum at . Further, in the case of a coin being tossed, it is likely that *p* will be not far from 0.5, so it is reasonable to take *p*=0.5 in the following:

And hence the value of maximum error (E) is given by

Solving for the required number of coin tosses, *n*,

Read more about this topic: Checking Whether A Coin Is Fair

### Famous quotes containing the words true and/or probability:

“The *true* poet for me is a priest. As soon as he dons the cassock, he must leave his family.”

—Gustave Flaubert (1821–1880)

“Crushed to earth and rising again is an author’s gymnastic. Once he fails to struggle to his feet and grab his pen, he will contemplate a fact he should never permit himself to face: that in all *probability* books have been written, are being written, will be written, better than anything he has done, is doing, or will do.”

—Fannie Hurst (1889–1968)