**Introduction**

Scholars are expected to pursue a research program and to contribute the results of their investigations to the scholarly record of their disciplines.The best estimate of scientific impact could be gained by an analysis of a researcher's total contributions carried out by qualified peers.

This is usually not feasible, so interest has focused on devising a "second best" method. Such a method is often referred to as a "metric", and a number of candidate metrics have been proposed. The word itself implies measurement, quantitation and arrangement on a scale. This guide discusses the advantages and drawbacks of several metrics.

**Characteristics of a Useful Metric**

To be useful, an evaluation metric should be:

- Objectively derived
- Simple to calculate
- Consistently applied
- Fair

The metric should arise from some established body of data and the method used should be explained. Deriving the metric should not require complicated techniques or take a long time. The same metric should be applied to all, in all cases. Research traditions of various disciplines should be respected in comparisons across disciplines.

**Metrics Rely on the Scientific Literature**

Candidate methods for establishing research impact generally rely on some form of **bibliometrics**, or the mathematical or statistical analysis of a portion of the scholarly record. Among the most common methods of estimating research impact are:

**Author Level Metrics** |
**Journal Level Metrics** |

Publication Count |
Impact Factor |

Citation Count |
Eigenfactor/Article Influence |

h-index |
CiteScore |

g-index |
SJR (SCImago Journal Rank) |

i10-index |
Source Normalized Impact per Paper (SNIP) |

**Each of these has advantages and drawbacks.**