Translation quality statistics

This page aims to give an overview of the quality of various translators available in the Apertium platform.

The metrics used here don't tell the whole story – see Evaluation for some discussion of strengths and limitations of WER/BLEU.

Quality Evaluations

These measures are used in the table below:

• Word Error Rate (WER) and Position-independent Word Error Rate (PWER) are measures of post-edition effort. The number gives the expected number of words needed to be corrected in 100 words of running text. So, a WER of 4.7% indicates that in a given 100 words of text, 4.7 of them will need to be corrected by the post-editor – for WER, lower is better.
• Bilingual Evaluation Understudy (BLEU) varies from 0 (bad) to 1 (perfect), so for BLEU, higher is better.

Precise numbers may vary due to differences in how sentences are selected to be evaluated. In some pairs, unknown words may be taken into account, in others not. Evaluations where unknown words are allowed will likely give me accurate numbers for postedition error, providing the corpus on which the evaluation was made resembles the corpus on which further translations will be made. Evaluations not allowing unknown words will give a better indication of "best-case" working of transfer rules.

Translator	Date	Version	Direction	Unknown words	WER	PWER	BLEU	Reference / Notes
apertium-eo-fr	11th February 2011		fr → eo	Yes	22.4 %	20.6 %	-	French_and_Esperanto/Quality_tests
			eo → fr		-	-	-
apertium-mk-en	19th September 2010	0.1.0	mk → en	No	43.96%	31.22%	-	Percentage is average of 1,000 words from SETimes and 1,000 from Wikipedia
			en → mk		-	-
apertium-mk-bg	31st August 2010	0.1.0	mk → bg	Yes	26.67 %	25.39 %	-	-
			bg → mk		-	-
apertium-nno-nob	12th October 2009	0.6.1	nno → nob	Yes	-	-	-	Unhammer and Trosterud, 2009 (two reference translations). 2021 Update: As of Nov 2021 the same test set gives 0.862±0.011. 2024 Update: As of June 2024, apertium-nno-nob from git used to translate fresh news articles had WER below 0.6 % (so on average, every 166th word needed altering)
			nob → nno		32.5%, 17.7%	-	0.74
apertium-br-fr	March 2010	0.2.0	br → fr	No	38 %	22 %	-	Tyers, 2010
			fr → br		-	-	-
apertium-sv-da	12th October 2009	0.5.0	sv → da	Yes	30.3 %	27.7 %	-	Swedish_and_Danish/Evaluation
			da → sv		-	-	-
apertium-eu-es	2nd September 2009		eu → es	Unknown	72.4 %	39.8 %	-	Ginestí-Rosell et al., 2009
			es → eu		-	-	-
apertium-cy-en	2nd January 2009		cy → en	Unknown	55.7 %	30.5 %	-	Tyers and Donnelly, 2009
			en → cy		-	-	-
apertium-eo-en	8th May 2009	0.9.0	en → eo	Unknown	21.0 %	19,0 %	-	English_and_Esperanto/Evaluation
			eo → en		-	-	-
apertium-es-pt	15th May 2006		es → pt	Unknown	4.7 %	-	-	Armentano et al., 2006
			pt → es		11.3 %	-	-
apertium-oc-ca	10th May 2006		oc → ca	Unknown	9.6 %	-	-	Armentano and Forcada, 2006
			ca → oc		-	-	-
apertium-pt-ca	28th July 2008		pt → ca	Unknown	16.6%	-	-	Armentano and Forcada, 2008
			ca → pt		14.1%	-	-
apertium-en-es	May 2009		en → es	Unknown	-	-	0.1851	Sánchez-Martínez, 2009
			es → en		-	-	0.1881

Coverage and Dictionary size

The number of entries in a dictionary, as well as the number of corpus forms that get some analysis, may give an indication of the maturity of a language pair.

For most dictionaries, there are numbers at least for dictionary size on the wiki, some also have coverage stats, see Category:Datastats. The stats of a certain apertium package will have a page with that package name (the name of the repository in GitHub) followed by "/stats", e.g. apertium-es-ca/stats. Some language pairs are split into several packages, so for nno-nob, there are pages apertium-nno, apertium-nob and apertium-nno-nob, but for dictionary counts you should consult the last one.

(Stats pages currently do not show number of CG or transfer rules.)

Usage Stats

The apertium.org usage stats give some indication of which pairs have the most users, which in turn might say something about quality. However, there may be various reasons for why a pair sees a lot or little use:

• some pairs are only offered for free by Apertium (e.g. nob-nno)
• for some pairs, there are very few speakers of one of the languages (though the pair itself may have high quality)
• and, of course some pairs simply have very good quality (e.g. spa-cat)

References

• Armentano-Oller, C., Carrasco, R. C. Corbí-Bellot, A. M., Forcada, M. L., Ginestí-Rosell, M., Ortiz-Rojas, S., Pérez-Ortiz, J. A., Ramírez-Sánchez, G., Sánchez-Martínez, F., Scalco, M. A. (2006) "Open-source Portuguese-Spanish machine translation", in In Lecture Notes in Computer Science 3960 (Computational Processing of the Portuguese Language, Proceedings of the 7th International Workshop on Computational Processing of Written and Spoken Portuguese, PROPOR 2006), May 13-17, 2006, ME - RJ / Itatiaia, Rio de Janeiro, Brazil. , p. 50-59
• Armentano-Oller, C. and Forcada, M. L. (2006) "Open-source machine translation between small languages: Catalan and Aranese Occitan", in Strategies for developing machine translation for minority languages (5th SALTMIL workshop on Minority Languages) (organized in conjunction with LREC 2006 (22-28.05.2006)) , p. 51-54
• Armentano-Oller, C., M.L. Forcada, "Reutilización de datos lingüísticos para la creación de un sistema de traducción automática para un nuevo par de lenguas", Procesamiento del Lenguaje Natural, :41, 243-250
• Ginestí-Rosell, M. and Ramírez-Sánchez, G. and Ortiz-Rojas, S. and Tyers, F. M. and Forcada, M. L. (2009) "Development of a free Basque to Spanish machine translation system". Procesamiento de Lenguaje Natural. No. 43, pp. 185--197
• Tyers, F. M. and Donnelly, K. (2009) "apertium-cy - a collaboratively-developed free RBMT system for Welsh to English". The Prague Bulletin of Mathematical Linguistics No. 91, pp. 57--66.
• Sánchez-Martínez Felipe; Mikel L. Forcada; Andy Way. "Hybrid rule-based ‒ example-based MT: Feeding Apertium with sub-sentential translation units". In Proceedings of the 3rd Workshop on Example-Based Machine Translation, p. 11-18, November 12-13, 2009, Dublin, Ireland.
• Unhammer, Kevin; Trosterud, Trond. "Reuse of free resources in machine translation between Nynorsk and Bokmål". In: Proceedings of the First International Workshop on Free/Open-Source Rule-Based Machine Translation / Edited by Juan Antonio Pérez-Ortiz, Felipe Sánchez-Martínez, Francis M. Tyers. Alicante : Universidad de Alicante. Departamento de Lenguajes y Sistemas Informáticos, 2009, pp. 35-42