# Comparisons of two age readers or two aging methods

### Description

Function compares graphically the readings of two age readers and calculates 2 chi-square statistics for tests of symmetry.

### Usage

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### Arguments

`readings` |
dataframe or matrix containing the readings by Reader 1 and those by Reader 2. |

`usecols` |
columns of the dataframe or matrix corresponding to the readings of Reader 1 and those of Reader 2. Default=c(1,2). |

`twovsone` |
logical for whether first type of graph is produced. |

`plot.summary` |
logical for whether summary table is put on first graph. |

`barplot` |
logical for whether barplot of frequency of disagreements is drawn. |

`chi` |
logical for whether 2 chi-square tests are performed. |

`pool.criterion` |
used to collapse pairs where the expected number of observations is < pooling criterion (default is 1). |

`cont.cor ` |
logical for whether a continuity correction should be used in 1st chisquare test. |

`correct` |
character for whether "Yates" or "Edwards" continuity correction should be done (if cont.cor=TRUE). |

`first.name` |
character string describing the first reader or the first aging method. The default is to specify "Reader A". |

`second.name` |
character string describing the second reader or the second aging method. The default is to specify "Reader B". |

### Details

This function can plot the number of readings of age j by reader 2 versus the number of readings of age i by reader 1 (if twovsone=TRUE). Optionally, it will add the number of readings above, on, and below the 45 degree line (if plot.summary=TRUE). The function can make a histogram of the differences in readings (if barplot=TRUE). Finally, the program can calculate 2 chi-square test statistics for tests of the null hypothesis that the two readers are interchangeable vs the alternative that there are systematic differences between readers (if chi=TRUE). The tests are tests of symmetry (Evans and Hoenig, 1998). If cont.cor=T, then correction for continuity is applied to the McNemar-like chi-square test statistic; the default is to apply the Yates correction but if correct="Edwards" is specified then the correction for continuity is 1.0 instead of 0.5.

### Value

Separate lists with tables of various statistics associated with the method.

### Author(s)

John Hoenig, Virginia Institute of Marine Science, 18 December 2012. hoenig@vims.edu

### References

Evans, G.T. and J.M. Hoenig. 1998. Viewing and Testing Symmetry in Contingency Tables, with Application to Fish Ages. Biometrics 54:620-629.).

### Examples

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