Comprehensive Research Report & Full Ablation Study
This repository contains NLP models trained and evaluated by Wikilangs, specifically on Tok Pisin 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
765
9.58
1,782
41.8%
85.7%
2-gram
Subword
220 🏆
7.78
1,423
75.2%
99.3%
3-gram
Word
1,436
10.49
2,504
30.0%
71.1%
3-gram
Subword
1,252
10.29
7,330
36.8%
80.5%
4-gram
Word
3,719
11.86
5,474
17.7%
43.3%
4-gram
Subword
4,262
12.06
25,004
24.7%
57.2%
5-gram
Word
3,008
11.55
4,258
18.3%
44.4%
5-gram
Subword
7,473
12.87
36,235
20.2%
48.1%
Top 5 N-grams by Size
2-grams (Word):
Rank
N-gram
Count
1
em i
1,565
2
ol i
502
3
i gat
454
4
i bin
429
5
i wanpela
353
3-grams (Word):
Rank
N-gram
Count
1
em i wanpela
277
2
em i intanet
170
3
i intanet kod
169
4
intanet kod bilong
168
5
i stap long
152
4-grams (Word):
Rank
N-gram
Count
1
em i intanet kod
169
2
i intanet kod bilong
168
3
intanet kod bilong kantri
150
4
emi wanpela taun long
77
5
na león spen provins
73
5-grams (Word):
Rank
N-gram
Count
1
em i intanet kod bilong
168
2
i intanet kod bilong kantri
150
3
provins castile na león spen
73
4
castile na león spen provins
73
5
wanpela taun long soria provins
70
2-grams (Subword):
Rank
N-gram
Count
1
n g
9,784
2
o n
9,572
3
i _
8,914
4
l o
8,912
5
a _
8,788
3-grams (Subword):
Rank
N-gram
Count
1
n g _
8,594
2
o n g
8,176
3
l o n
8,105
4
_ i _
4,901
5
_ b i
4,777
4-grams (Subword):
Rank
N-gram
Count
1
l o n g
8,042
2
o n g _
7,994
3
_ l o n
4,532
4
_ b i l
3,254
5
i l o n
3,199
5-grams (Subword):
Rank
N-gram
Count
1
l o n g _
7,945
2
_ l o n g
4,521
3
_ b i l o
3,195
4
b i l o n
3,195
5
i l o n g
3,194
Key Findings
Best Perplexity: 2-gram (subword) with 220
Entropy Trend: Decreases with larger n-grams (more predictable)
Coverage: Top-1000 patterns cover ~48% 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
0.6340
1.552
3.43
10,055
36.6%
1
Subword
0.6982
1.622
4.77
907
30.2%
2
Word
0.2413
1.182
1.52
34,078
75.9%
2
Subword
0.7924
1.732
4.03
4,305
20.8%
3
Word
0.0987
1.071
1.16
51,273
90.1%
3
Subword
0.6704
1.591
2.82
17,280
33.0%
4
Word
0.0388 🏆
1.027
1.05
58,656
96.1%
4
Subword
0.4282
1.346
1.86
48,609
57.2%
Generated Text Samples (Word-based)
Below are text samples generated from each word-based Markov chain model:
Context Size 1:
i mas save pairap inglis molecule o latvijas republika latvija letonia lv sv toppdomän f bihain
long em ol kaikai long giraun papua niugini i save luksave olsem wanpela teritori bilong kantri
bilong zeus
Context Size 2:
em i wanpela distrik long is samar provins nau long taim ol i makim bill skate i
ol i yusim diatomit bilong wokim giaman stori bilong aeneas i gat mo rot tu tasol long
i gat biknem long lotu na bagarap na yumi igat rait long senisim asples o kantri inap
Context Size 3:
em i wanpela pasin bilong raitim ol tok olsem wan wan leta i makim wanpela krai dispela i
em i intanet kod bilong kantri siapan long esia 36 milion manmeri i stap abrus o waitpela manmeri
i intanet kod bilong kantri kiribas ki sv toppdomän k
Context Size 4:
em i intanet kod bilong kantri siamani de sv toppdomän d
i intanet kod bilong ascension insait kantri sen helena ascension na tristan da kuna ac
intanet kod bilong kantri solomon ailans slb
Generated Text Samples (Subword-based)
Below are text samples generated from each subword-based Markov chain model:
Context Size 1:
_тступоваув_5976
alelutaina_binge
i_блав_le_lon_vi
Context Size 2:
ng_kong_van_wan_t
ong_kripenis:_лек
i_lusianwanpeleón
Context Size 3:
ng_holimigur_20_49
ong_mp3_familipim_
long_manmeri_inter
Context Size 4:
long_graun_bikpela_
ong_diksen_bilong_s
_long_haus_wanpela_
Key Findings
Best Predictability: Context-4 (word) with 96.1% predictability
Branching Factor: Decreases with context size (more deterministic)
Memory Trade-off: Larger contexts require more storage (48,609 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
4,414
Total Tokens
68,197
Mean Frequency
15.45
Median Frequency
3
Frequency Std Dev
129.66
Most Common Words
Rank
Word
Frequency
1
i
4,945
2
long
4,543
3
bilong
3,174
4
na
2,044
5
em
2,006
6
ol
2,005
7
wanpela
937
8
kantri
793
9
tok
737
10
olsem
581
Least Common Words (from vocabulary)
Rank
Word
Frequency
1
iucn
2
2
tudakpela
2
3
haitim
2
4
transformer
2
5
pletfom
2
6
nintendo
2
7
return
2
8
deluxe
2
9
allies
2
10
forgotten
2
Zipf's Law Analysis
Metric
Value
Zipf Coefficient
1.0374
R² (Goodness of Fit)
0.984176
Adherence Quality
excellent
Coverage Analysis
Top N Words
Coverage
Top 100
58.9%
Top 1,000
85.6%
Top 5,000
0.0%
Top 10,000
0.0%
Key Findings
Zipf Compliance: R²=0.9842 indicates excellent adherence to Zipf's law
High Frequency Dominance: Top 100 words cover 58.9% of corpus
Long Tail: -5,586 words needed for remaining 100.0% 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
0.0778 🏆
0.6368
N/A
N/A
mono_64d
64
0.0142
0.6826
N/A
N/A
mono_128d
128
0.0027
0.6822
N/A
N/A
aligned_32d
32
0.0778
0.6434
0.0080
0.0900
aligned_64d
64
0.0142
0.6713
0.0120
0.0680
aligned_128d
128
0.0027
0.6897
0.0060
0.0560
Key Findings
Best Isotropy: mono_32d with 0.0778 (more uniform distribution)
Semantic Density: Average pairwise similarity of 0.6677. Lower values indicate better semantic separation.
Alignment Quality: Aligned models achieve up to 1.2% 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
-0.076
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
-s
sutim, stude, science
-p
ponoloji, papa, puławy
-b
bikpla, by, bringim
-m
montreal, mick, mindanao
-a
andersen, amamas, anderson
-k
katim, konversen, kainantu
-t
toledo, tuesday, territories
-ma
maui, mathew, masta
Productive Suffixes
Suffix
Examples
-a
despla, bikpla, papa
-n
circumcision, andersen, yunien
-s
opis, ogastas, territories
-e
stude, hangre, science
-m
sutim, lukautim, katim
-en
andersen, yunien, konversen
-an
giaman, independan, aislan
-l
montreal, medal, kaunsil
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
tpel
1.44x
7 contexts
etpela, retpela, sotpela
inim
1.38x
6 contexts
winim, minim, painim
arap
1.37x
6 contexts
narapla, bagarap, arapela
amba
1.35x
6 contexts
namba, nambafo, nambaut
namb
1.36x
5 contexts
namba, nambis, nambafo
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
-p
-n
27 words
palawan, plen
-m
-a
25 words
mipela, masta
-s
-a
23 words
sevilla, sta
-a
-n
22 words
andersen, anderson
-s
-n
21 words
sandaun, suwisalan
-s
-s
20 words
saiens, songs
-a
-a
18 words
aljiria, angila
-p
-a
17 words
papa, palencia
-b
-a
17 words
bikpla, brata
-k
-a
16 words
kaledonia, kompyuta
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
independans
independ-an-s
7.5
an
vientiane
vienti-an-e
7.5
an
pensilvania
pensilv-an-ia
7.5
an
filipinas
filipin-a-s
7.5
a
eksaminim
eksam-in-im
7.5
in
konstitusen
konstitu-s-en
7.5
s
deutschland
deutsch-la-nd
7.5
la
plantikain
planti-ka-in
7.5
ka
manmanmeri
m-an-manmeri
7.5
manmeri
toktokman
toktok-m-an
7.5
m
representim
re-present-im
6.0
present
periodical
periodic-al
4.5
periodic
champions
champion-s
4.5
champion
provinsel
provins-el
4.5
provins
internationale
international-e
4.5
international
6.6 Linguistic Interpretation
Automated Insight:
The language Tok Pisin 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
16k BPE
Best compression (4.04x)
N-gram
2-gram
Lowest perplexity (220)
Markov
Context-4
Highest predictability (96.1%)
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.
