Comprehensive Research Report & Full Ablation Study
This repository contains NLP models trained and evaluated by Wikilangs, specifically on Basque Wikipedia data.
We analyze tokenizers, n-gram models, Markov chains, vocabulary statistics, and word embeddings.
📋 Repository Contents
Models & Assets
Tokenizers (8k, 16k, 32k, 64k)
N-gram models (2, 3, 4, 5-gram)
Markov chains (context of 1, 2, 3, 4 and 5)
Subword N-gram and Markov chains
Embeddings in various sizes and dimensions (aligned and unaligned)
Trade-off: Larger vocabularies improve compression but increase model size
Recommendation: 32k vocabulary provides optimal balance for production use
2. N-gram Model Evaluation
N-gram Perplexity
N-gram Unique
N-gram Coverage
Results
N-gram
Variant
Perplexity
Entropy
Unique N-grams
Top-100 Coverage
Top-1000 Coverage
2-gram
Word
101,400
16.63
1,518,553
10.5%
31.4%
2-gram
Subword
226 🏆
7.82
17,699
72.3%
99.5%
3-gram
Word
128,394
16.97
2,211,893
10.6%
32.1%
3-gram
Subword
1,909
10.90
132,832
27.9%
76.3%
4-gram
Word
179,917
17.46
3,667,160
11.5%
30.7%
4-gram
Subword
10,807
13.40
755,000
12.9%
43.1%
5-gram
Word
134,161
17.03
2,865,762
13.8%
31.9%
5-gram
Subword
41,735
15.35
2,680,749
7.6%
27.1%
Top 5 N-grams by Size
2-grams (Word):
Rank
N-gram
Count
1
kanpo estekak
411,094
2
izan zen
219,794
3
bat da
194,039
4
ziren eta
172,147
5
enpresak ziren
157,767
3-grams (Word):
Rank
N-gram
Count
1
erreferentziak kanpo estekak
152,739
2
erreferentziak ikus gainera
78,821
3
ziren horien artean
67,157
4
gertuen dauden herriak
66,904
5
bakarrik bizi ziren
64,949
4-grams (Word):
Rank
N-gram
Count
1
dauden herriak erakusten ditu
33,543
2
honek gertuen dauden herriak
33,541
3
france par comune frantziako
33,541
4
par comune frantziako udalerri
33,541
5
diagrama honek gertuen dauden
33,540
5-grams (Word):
Rank
N-gram
Count
1
france par comune frantziako udalerri
33,541
2
diagrama honek gertuen dauden herriak
33,540
3
honek gertuen dauden herriak erakusten
33,540
4
gertuen dauden herriak erakusten ditu
33,540
5
emploi et population active et
33,539
2-grams (Subword):
Rank
N-gram
Count
1
e n
16,166,768
2
a _
14,488,655
3
n _
14,293,162
4
_ e
11,880,846
5
a r
11,450,376
3-grams (Subword):
Rank
N-gram
Count
1
e n _
8,377,081
2
k o _
5,400,285
3
e t a
5,000,482
4
r e n
4,339,867
5
a k _
4,189,214
4-grams (Subword):
Rank
N-gram
Count
1
e t a _
3,251,221
2
_ e t a
3,085,028
3
r e n _
2,969,339
4
a k o _
2,216,397
5
a r e n
2,019,670
5-grams (Subword):
Rank
N-gram
Count
1
_ e t a _
2,973,733
2
a r e n _
1,944,215
3
_ z i r e
942,772
4
z i r e n
928,644
5
t z e n _
881,836
Key Findings
Best Perplexity: 2-gram (subword) with 226
Entropy Trend: Decreases with larger n-grams (more predictable)
Coverage: Top-1000 patterns cover ~27% of corpus
Recommendation: 4-gram or 5-gram for best predictive performance
3. Markov Chain Evaluation
Markov Entropy
Markov Contexts
Markov Branching
Results
Context
Variant
Avg Entropy
Perplexity
Branching Factor
Unique Contexts
Predictability
1
Word
0.9814
1.974
11.89
2,034,056
1.9%
1
Subword
1.0508
2.072
6.91
11,299
0.0%
2
Word
0.3086
1.238
1.95
24,154,380
69.1%
2
Subword
0.6282
1.546
4.22
78,093
37.2%
3
Word
0.1002
1.072
1.21
46,969,150
90.0%
3
Subword
0.6997
1.624
4.08
329,201
30.0%
4
Word
0.0366 🏆
1.026
1.07
56,781,994
96.3%
4
Subword
0.6958
1.620
3.58
1,344,420
30.4%
Generated Text Samples (Word-based)
Below are text samples generated from each word-based Markov chain model:
Context Size 1:
eta 20 emakume aktoreak mikel jondoni joanes leizarraga izendatu zuten azpian 99 lanean hasi zen urt...
da horretan zangozako merindadean sartu zen 2 lizeo teknologiko asko horietako bi pertsona bakoitzek...
zen bertako zuzendaritzarekin doktoretza osatu zuen rayuela eleberri hauek erdialdeko asian dub duba...
Context Size 2:
kanpo estekak monasterioak arkitektura erromanikoa du iurreko amabirjina xii xiii orrialdeak jatorri...
izan zen 2 altzari dendak 1 altzari denda zen 1 liburu denda batean lan egiten zuen oso
bat da horn barrutian azken zentsuaren arabera hart udalerriak 823 etxebizitza zeuden 667 hektarea e...
Context Size 3:
erreferentziak kanpo estekak kategoria departamenduko kantonamenduak santuen lurraldea
erreferentziak ikus gainera porichthys batrachoididae kanpo estekak fishbase org arrainak golkoko ar...
ziren horien artean 39 aktiboak ziren eta 255 apartamentuak ziren 375 etxebizitza nagusietatik 310 b...
Context Size 4:
dauden herriak erakusten ditu batzuen distantzia eta kokapen erlatiboa erreferentziak kanpo estekak ...
par comune frantziako udalerri guztietako datu zehatzak mapa baten bitartez eskuragarri udalerriak o...
france par comune frantziako udalerri guztietako datu zehatzak mapa baten bitartez eskuragarri udale...
Generated Text Samples (Subword-based)
Below are text samples generated from each subword-based Markov chain model:
Context Size 1:
_dolaugetudagu-f
a_eahaianak_grel
e_mpeldo_seaskos
Context Size 2:
enpon_emailerako_
a_soa_danibola_bu
n_etak),_sa_caler
Context Size 3:
en_batua_utz_estek
ko_eta_gazioa_bili
eta_mota_apolibre_
Context Size 4:
eta_badituzten_adin
_eta_liburu_da,_adi
ren_aranoaren_kondu
Key Findings
Best Predictability: Context-4 (word) with 96.3% predictability
Branching Factor: Decreases with context size (more deterministic)
Memory Trade-off: Larger contexts require more storage (1,344,420 contexts)
Recommendation: Context-3 or Context-4 for text generation
4. Vocabulary Analysis
Zipf's Law
Top Words
Coverage Curve
Statistics
Metric
Value
Vocabulary Size
925,645
Total Tokens
82,551,722
Mean Frequency
89.18
Median Frequency
4
Frequency Std Dev
4334.93
Most Common Words
Rank
Word
Frequency
1
eta
3,064,757
2
da
1,077,465
3
zen
1,014,999
4
ziren
906,527
5
bat
694,872
6
zuen
667,830
7
izan
539,156
8
zeuden
442,816
9
kanpo
430,370
10
1
427,974
Least Common Words (from vocabulary)
Rank
Word
Frequency
1
pveducation
2
2
chillijchi
2
3
gaureguneko
2
4
cupla
2
5
marwareraren
2
6
vaṇī
2
7
antarātmā
2
8
ले
2
9
ओमन
2
10
barbajuan
2
Zipf's Law Analysis
Metric
Value
Zipf Coefficient
1.0446
R² (Goodness of Fit)
0.993920
Adherence Quality
excellent
Coverage Analysis
Top N Words
Coverage
Top 100
27.0%
Top 1,000
53.3%
Top 5,000
70.7%
Top 10,000
77.4%
Key Findings
Zipf Compliance: R²=0.9939 indicates excellent adherence to Zipf's law
High Frequency Dominance: Top 100 words cover 27.0% of corpus
Long Tail: 915,645 words needed for remaining 22.6% coverage
5. Word Embeddings Evaluation
Embedding Isotropy
Similarity Matrix
t-SNE Words
t-SNE Sentences
5.1 Cross-Lingual Alignment
Alignment Quality
Multilingual t-SNE
5.2 Model Comparison
Model
Dimension
Isotropy
Semantic Density
Alignment R@1
Alignment R@10
mono_32d
32
0.6711
0.3672
N/A
N/A
mono_64d
64
0.6503
0.2977
N/A
N/A
mono_128d
128
0.5876
0.2512
N/A
N/A
aligned_32d
32
0.6711 🏆
0.3650
0.3080
0.7260
aligned_64d
64
0.6503
0.3045
0.5360
0.8520
aligned_128d
128
0.5876
0.2534
0.6260
0.8780
Key Findings
Best Isotropy: aligned_32d with 0.6711 (more uniform distribution)
Semantic Density: Average pairwise similarity of 0.3065. Lower values indicate better semantic separation.
Alignment Quality: Aligned models achieve up to 62.6% R@1 in cross-lingual retrieval.
Recommendation: 128d aligned for best cross-lingual performance
6. Morphological Analysis (Experimental)
This section presents an automated morphological analysis derived from the statistical divergence between word-level and subword-level models. By analyzing where subword predictability spikes and where word-level coverage fails, we can infer linguistic structures without supervised data.
6.1 Productivity & Complexity
Metric
Value
Interpretation
Recommendation
Productivity Index
5.000
High morphological productivity
Reliable analysis
Idiomaticity Gap
0.176
Low formulaic content
-
6.2 Affix Inventory (Productive Units)
These are the most productive prefixes and suffixes identified by sampling the vocabulary for global substitutability patterns. A unit is considered an affix if stripping it leaves a valid stem that appears in other contexts.
Productive Prefixes
Prefix
Examples
-a
alienak, alalpardo, azhkhluttach
-s
spiritist, stateira, sakanari
-ma
maezturekin, malasiako, malaciotis
-m
miyashita, mwir, maezturekin
-e
eakoak, euskeras, enacryos
-b
birjinarenak, budavari, blechnerren
-ba
bagoiaren, balazten, banús
-t
txingorrigain, tdpm, t280
Productive Suffixes
Suffix
Examples
-n
ultraeskuindarrarekin, blechnerren, borbónen
-en
blechnerren, borbónen, aynen
-a
miyashita, prestatzera, haparanda
-k
eakoak, birjinarenak, paraxialetik
-o
villasecako, sakonuneetako, alalpardo
-ko
villasecako, sakonuneetako, malasiako
-ak
eakoak, birjinarenak, alienak
-in
ultraeskuindarrarekin, uzkiarekin, txingorrigain
6.3 Bound Stems (Lexical Roots)
Bound stems are high-frequency subword units that are semantically cohesive but rarely appear as standalone words. These often correspond to the 'core' of a word that requires inflection or derivation to be valid.
Stem
Cohesion
Substitutability
Examples
rtze
1.71x
538 contexts
artze, ertze, urtze
tuzt
2.70x
47 contexts
tuzte, dituzt, dtuzte
ikoa
1.67x
501 contexts
aikoa, oikoa, pikoa
eude
2.63x
45 contexts
eudes, zeude, eudel
oare
1.66x
385 contexts
hoare, soare, joare
anle
2.52x
48 contexts
nanle, anleu, zhanle
atut
1.69x
284 contexts
matute, batuta, statut
iare
1.49x
539 contexts
tiare, iaren, iaret
ntza
1.57x
373 contexts
intza, antza, ontza
rria
1.54x
343 contexts
irria, erria, orria
tanl
2.47x
30 contexts
tanlay, stanly, bitanle
ituz
1.75x
106 contexts
dituz, dituzu, abituz
6.4 Affix Compatibility (Co-occurrence)
This table shows which prefixes and suffixes most frequently co-occur on the same stems, revealing the 'stacking' rules of the language's morphology.
Prefix
Suffix
Frequency
Examples
-a
-n
188 words
ahtren, anbiguoen
-e
-n
162 words
epilepsiarekin, ensoren
-a
-a
136 words
austfonna, alotropia
-b
-n
121 words
bizitasunaren, bayaniren
-k
-n
111 words
koltxoiaren, kiroltasunaren
-s
-n
105 words
selekzioaren, solasaldien
-a
-k
102 words
arrazek, artxuk
-e
-k
101 words
eszenaratzeagatik, eskumikaturik
-e
-a
99 words
eulychnia, elgetarra
-p
-n
97 words
presidenteordetzan, pobrezian
6.5 Recursive Morpheme Segmentation
Using Recursive Hierarchical Substitutability, we decompose complex words into their constituent morphemes. This approach handles nested affixes (e.g., prefix-prefix-root-suffix).
Word
Suggested Split
Confidence
Stem
domeinuan
domeinu-a-n
7.5
a
aritmometroa
aritmometr-o-a
7.5
o
maratoiean
maratoi-e-an
7.5
e
goenagari
goenag-a-ri
7.5
a
onenerako
onener-a-ko
7.5
a
networken
networ-k-en
7.5
k
yamatentomon
yamatentom-o-n
7.5
o
sulfurozkoa
sulfuroz-ko-a
7.5
ko
entzunezkoak
entzunez-ko-ak
7.5
ko
esparruetako
esparruet-a-ko
7.5
a
ezereztasuna
ezereztasu-n-a
7.5
n
mugagabetasuna
mugagabetasu-n-a
7.5
n
zutabeari
zutabe-a-ri
7.5
a
rouxestevae
rouxestev-a-e
7.5
a
karrantzara
karrantz-a-ra
7.5
a
6.6 Linguistic Interpretation
Automated Insight:
The language Basque shows high morphological productivity. The subword models are significantly more efficient than word models, suggesting a rich system of affixation or compounding.
7. Summary & Recommendations
Performance Dashboard
Production Recommendations
Component
Recommended
Rationale
Tokenizer
64k BPE
Best compression (4.51x)
N-gram
2-gram
Lowest perplexity (226)
Markov
Context-4
Highest predictability (96.3%)
Embeddings
100d
Balanced semantic capture and isotropy
Appendix: Metrics Glossary & Interpretation Guide
This section provides definitions, intuitions, and guidance for interpreting the metrics used throughout this report.
Tokenizer Metrics
Compression Ratio
Definition: The ratio of characters to tokens (chars/token). Measures how efficiently the tokenizer represents text.
Intuition: Higher compression means fewer tokens needed to represent the same text, reducing sequence lengths for downstream models. A 3x compression means ~3 characters per token on average.
What to seek: Higher is generally better for efficiency, but extremely high compression may indicate overly aggressive merging that loses morphological information.
Average Token Length (Fertility)
Definition: Mean number of characters per token produced by the tokenizer.
Intuition: Reflects the granularity of tokenization. Longer tokens capture more context but may struggle with rare words; shorter tokens are more flexible but increase sequence length.
What to seek: Balance between 2-5 characters for most languages. Arabic/morphologically-rich languages may benefit from slightly longer tokens.
Unknown Token Rate (OOV Rate)
Definition: Percentage of tokens that map to the unknown/UNK token, indicating words the tokenizer cannot represent.
Intuition: Lower OOV means better vocabulary coverage. High OOV indicates the tokenizer encounters many unseen character sequences.
What to seek: Below 1% is excellent; below 5% is acceptable. BPE tokenizers typically achieve very low OOV due to subword fallback.
N-gram Model Metrics
Perplexity
Definition: Measures how "surprised" the model is by test data. Mathematically: 2^(cross-entropy). Lower values indicate better prediction.
Intuition: If perplexity is 100, the model is as uncertain as if choosing uniformly among 100 options at each step. A perplexity of 10 means effectively choosing among 10 equally likely options.
What to seek: Lower is better. Perplexity decreases with larger n-grams (more context). Values vary widely by language and corpus size.
Entropy
Definition: Average information content (in bits) needed to encode the next token given the context. Related to perplexity: perplexity = 2^entropy.
Intuition: High entropy means high uncertainty/randomness; low entropy means predictable patterns. Natural language typically has entropy between 1-4 bits per character.
What to seek: Lower entropy indicates more predictable text patterns. Entropy should decrease as n-gram size increases.
Coverage (Top-K)
Definition: Percentage of corpus occurrences explained by the top K most frequent n-grams.
Intuition: High coverage with few patterns indicates repetitive/formulaic text; low coverage suggests diverse vocabulary usage.
What to seek: Depends on use case. For language modeling, moderate coverage (40-60% with top-1000) is typical for natural text.
Markov Chain Metrics
Average Entropy
Definition: Mean entropy across all contexts, measuring average uncertainty in next-word prediction.
Intuition: Lower entropy means the model is more confident about what comes next. Context-1 has high entropy (many possible next words); Context-4 has low entropy (few likely continuations).
What to seek: Decreasing entropy with larger context sizes. Very low entropy (<0.1) indicates highly deterministic transitions.
Branching Factor
Definition: Average number of unique next tokens observed for each context.
Intuition: High branching = many possible continuations (flexible but uncertain); low branching = few options (predictable but potentially repetitive).
What to seek: Branching factor should decrease with context size. Values near 1.0 indicate nearly deterministic chains.
Predictability
Definition: Derived metric: (1 - normalized_entropy) × 100%. Indicates how deterministic the model's predictions are.
Intuition: 100% predictability means the next word is always certain; 0% means completely random. Real text falls between these extremes.
What to seek: Higher predictability for text generation quality, but too high (>98%) may produce repetitive output.
Vocabulary & Zipf's Law Metrics
Zipf's Coefficient
Definition: The slope of the log-log plot of word frequency vs. rank. Zipf's law predicts this should be approximately -1.
Intuition: A coefficient near -1 indicates the corpus follows natural language patterns where a few words are very common and most words are rare.
What to seek: Values between -0.8 and -1.2 indicate healthy natural language distribution. Deviations may suggest domain-specific or artificial text.
R² (Coefficient of Determination)
Definition: Measures how well the linear fit explains the frequency-rank relationship. Ranges from 0 to 1.
Intuition: R² near 1.0 means the data closely follows Zipf's law; lower values indicate deviation from expected word frequency patterns.
What to seek: R² > 0.95 is excellent; > 0.99 indicates near-perfect Zipf adherence typical of large natural corpora.
Vocabulary Coverage
Definition: Cumulative percentage of corpus tokens accounted for by the top N words.
Intuition: Shows how concentrated word usage is. If top-100 words cover 50% of text, the corpus relies heavily on common words.
What to seek: Top-100 covering 30-50% is typical. Higher coverage indicates more repetitive text; lower suggests richer vocabulary.
Word Embedding Metrics
Isotropy
Definition: Measures how uniformly distributed vectors are in the embedding space. Computed as the ratio of minimum to maximum singular values.
Intuition: High isotropy (near 1.0) means vectors spread evenly in all directions; low isotropy means vectors cluster in certain directions, reducing expressiveness.
What to seek: Higher isotropy generally indicates better-quality embeddings. Values > 0.1 are reasonable; > 0.3 is good. Lower-dimensional embeddings tend to have higher isotropy.
Average Norm
Definition: Mean magnitude (L2 norm) of word vectors in the embedding space.
Intuition: Indicates the typical "length" of vectors. Consistent norms suggest stable training; high variance may indicate some words are undertrained.
What to seek: Relatively consistent norms across models. The absolute value matters less than consistency (low std deviation).
Cosine Similarity
Definition: Measures angular similarity between vectors, ranging from -1 (opposite) to 1 (identical direction).
Intuition: Words with similar meanings should have high cosine similarity. This is the standard metric for semantic relatedness in embeddings.
What to seek: Semantically related words should score > 0.5; unrelated words should be near 0. Synonyms often score > 0.7.
t-SNE Visualization
Definition: t-Distributed Stochastic Neighbor Embedding - a dimensionality reduction technique that preserves local structure for visualization.
Intuition: Clusters in t-SNE plots indicate groups of semantically related words. Spread indicates vocabulary diversity; tight clusters suggest semantic coherence.
What to seek: Meaningful clusters (e.g., numbers together, verbs together). Avoid over-interpreting distances - t-SNE preserves local, not global, structure.
General Interpretation Guidelines
Compare within model families: Metrics are most meaningful when comparing models of the same type (e.g., 8k vs 64k tokenizer).
Consider trade-offs: Better performance on one metric often comes at the cost of another (e.g., compression vs. OOV rate).
Context matters: Optimal values depend on downstream tasks. Text generation may prioritize different metrics than classification.
Corpus influence: All metrics are influenced by corpus characteristics. Wikipedia text differs from social media or literature.
Language-specific patterns: Morphologically rich languages (like Arabic) may show different optimal ranges than analytic languages.
Visualizations Index
Visualization
Description
Tokenizer Compression
Compression ratios by vocabulary size
Tokenizer Fertility
Average token length by vocabulary
Tokenizer OOV
Unknown token rates
Tokenizer Total Tokens
Total tokens by vocabulary
N-gram Perplexity
Perplexity by n-gram size
N-gram Entropy
Entropy by n-gram size
N-gram Coverage
Top pattern coverage
N-gram Unique
Unique n-gram counts
Markov Entropy
Entropy by context size
Markov Branching
Branching factor by context
Markov Contexts
Unique context counts
Zipf's Law
Frequency-rank distribution with fit
Vocab Frequency
Word frequency distribution
Top 20 Words
Most frequent words
Vocab Coverage
Cumulative coverage curve
Embedding Isotropy
Vector space uniformity
Embedding Norms
Vector magnitude distribution
Embedding Similarity
Word similarity heatmap
Nearest Neighbors
Similar words for key terms
t-SNE Words
2D word embedding visualization
t-SNE Sentences
2D sentence embedding visualization
Position Encoding
Encoding method comparison
Model Sizes
Storage requirements
Performance Dashboard
Comprehensive performance overview
About This Project
Data Source
Models trained on wikipedia-monthly - a monthly snapshot of Wikipedia articles across 300+ languages.
Project
A project by Wikilangs - Open-source NLP models for every Wikipedia language.
