# Statistics used in computing and drawing a Shewhart g chart

### Description

These functions are used to compute statistics required by the g chart (geometric distribution) for use with the qcc package.

### Usage

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### Arguments

`data` |
the observed data values |

`center` |
sample center statistic |

`sizes` |
sample sizes (not used) |

`std.dev` |
standard deviation of geometric distribution |

`conf` |
a numeric value used to compute control limits, specifying the number of standard deviations (if 'conf' > 1) or the confidence level (if 0 < 'conf' < 1). |

`...` |
further arguments are ignored. |

### Details

The g chart plots the number of non-events between events. np charts do not work well when the probability of an event is rare (see example below). Instead of plotting the number of events, the g chart plots the number of non-events between events.

### Value

The function `stats.g()`

returns a list with components `statistics`

and `center`

.

The function `sd.g()`

returns `std.dev`

the standard deviation
*sqrt(1-p)/p*.

The function `limits.g()`

returns a matrix with lower and upper control limits.

### Note

The geometric distribution is quite skewed so it is best to set conf at the required confidence interval (0 < conf < 1) rather than as a multiplier of sigma.

### Author(s)

Greg Snow greg.snow@ihc.com

### References

Kaminsky, FC et. al. (1992) *Statistical Control Charts Based on a Geometric Distribution*, Journal of Quality Technology, 24, pp 63–69.

Yang, Z et. al. (2002) On the Performance of Geometric Charts with
Estimated Control Limits, *Journal of Quality Technology*, 34, pp 448–458.

### See Also

`qcc`

### Examples

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