_model: slides
---

title: CSCI 577 - Data Mining

---
body:

# Political Polarization 

Matt Jensen

===

# Hypothesis 

Political polarization is rising, and news articles are a proxy measure.

==

# Is this reasonable? 


==

# Why is polarization rising? 

Not my job, but there's research<sup>[ref](#references)</sup> to support it


==

# Sub-hypothesis 

- The polarization increases near elections. <!-- .element: class="fragment" -->
- The polarization is not evenly distributed across publishers. <!-- .element: class="fragment" -->
- The polarization is not evenly distributed across political specturm. <!-- .element: class="fragment" -->

==

# Sub-sub-hypothesis 

- Similarly polarized publishers link to each other. <!-- .element: class="fragment" -->
- 'Mainstream' media uses more neutral titles. <!-- .element: class="fragment" -->
- Highly polarized publications don't last as long. <!-- .element: class="fragment" -->

===

# Data Source(s) 

memeorandum.com <!-- .element: class="fragment" -->

allsides.com <!-- .element: class="fragment" -->

huggingface.com <!-- .element: class="fragment" -->

Note:
Let's get a handle on the shape of the data.

The sources, size, and features of the data.

===

<section data-background-iframe="https://www.memeorandum.com" data-background-interactive></section>

===

# memeorandum.com

- News aggregation site. <!-- .element: class="fragment" -->
- Was really famous before Google News. <!-- .element: class="fragment" -->
- Still aggregates sites today. <!-- .element: class="fragment" -->

==

# Why Memeorandum? 

- Behavioral: I only read titles sometimes. (doom scrolling). <!-- .element class="fragment" -->
- Behavioral: It's my source of news (with sister site TechMeme.com). <!-- .element class="fragment" -->
- Convenient: most publishers block bots. <!-- .element class="fragment" -->
- Convenient: dead simple html to parse. <!-- .element class="fragment" -->
- Archival: all headlines from 2006 forward. <!-- .element class="fragment" -->
- Archival: automated, not editorialized. <!-- .element class="fragment" -->

===

<section data-background-iframe="https://www.allsides.com/media-bias/ratings" data-background-interactive></section>

===

# AllSides.com

- Rates news publications as left, center or right. <!-- .element: class="fragment" -->
- Ratings combine: <!-- .element: class="fragment" -->
    - blind bias surveys.
    - editorial reviews.
    - third party research.
    - community voting.
- Originally scraped website, but direct access eventually. <!-- .element: class="fragment" -->


==

# Why AllSides? 

- Behavioral: One of the first google results on bias apis. <!-- .element class="fragment" -->
- Convenient: Ordinal ratings [-2: very left, 2: very right]. <!-- .element class="fragment" -->
- Convenient: Easy format. <!-- .element class="fragment" -->
- Archival: Covers 1400 publishers. <!-- .element class="fragment" -->

===

<section data-background-iframe="https://huggingface.co/models" data-background-interactive></section>

===

# HuggingFace.com

- Deep Learning library. <!-- .element: class="fragment" -->
- Lots of pretrained models. <!-- .element: class="fragment" -->
- Easy, off the shelf word/sentence embeddings and text classification models. <!-- .element: class="fragment" -->

==

# Why HuggingFace? 

- Behavioral: Language Models are HOT right now. <!-- .element: class="fragment" -->
- Behavioral: The dataset needed more features.<!-- .element: class="fragment" -->
- Convenient: Literally 5 lines of python.<!-- .element: class="fragment" -->
- Convenient: Testing different model performance was easy.<!-- .element: class="fragment" -->
- Archival: Lots of pretrained classification tasks.<!-- .element: class="fragment" -->

===

# Data Structures
## Stories

- Top level stories. <!-- .element: class="fragment" -->
    - title.
    - publisher.
    - author.
- Related discussion. <!-- .element: class="fragment" -->
    - publisher.
    - uses 'parent' story as a source.
- Stream of stories (changes constantly). <!-- .element: class="fragment" -->

==

# Data Structures
## Bias

- Per publisher. <!-- .element: class="fragment" -->
    - name.
    - label.
    - agree/disagree vote by community. 
- Name could be semi-automatically joined to stories. <!-- .element: class="fragment" -->

==

# Data Structures
## Embeddings

- Per story title. <!-- .element: class="fragment" -->
    - sentence embedding (n, 384).
    - sentiment classification (n, 1).
    - emotional classification (n, 1).
- ~ 1 hour of inference time to map story titles and descriptions. <!-- .element: class="fragment" -->

===

# Data Collection

==

# Data Collection

## Story Scraper (simplified)

```python
day = timedelta(days=1)
cur = date(2005, 10, 1)
end = date.today()
while cur <= end:
    cur = cur + day
    save_as = output_dir / f"{cur.strftime('%y-%m-%d')}.html"
    url = f"https://www.memeorandum.com/{cur.strftime('%y%m%d')}/h2000"
    r = requests.get(url)
    with open(save_as, 'w') as f:
        f.write(r.text)
```

==

# Data Collection

## Bias Scraper (hard)

```python
...
bias_html = DATA_DIR / 'allsides.html'
parser = etree.HTMLParser()
tree = etree.parse(str(bias_html), parser)
root = tree.getroot()
rows = root.xpath('//table[contains(@class,"views-table")]/tbody/tr')

ratings = []
for row in rows:
    rating = dict()
    ...
```

==

# Data Collection

## Bias Scraper (easy)

![allsides request](https://studentweb.cs.wwu.edu/~jensen33/static/577/allsides_request.png)

==

# Data Collection

## Embeddings (easy)

```python
# table = ...
tokenizer = AutoTokenizer.from_pretrained("roberta-base")
model = AutoModel.from_pretrained("roberta-base")

for chunk in table:
    tokens = tokenizer(chunk, add_special_tokens = True, truncation = True, padding = "max_length", max_length=92, return_attention_mask = True, return_tensors = "pt")
    outputs = model(**tokens)
    embeddings = outputs.last_hidden_state.detach().numpy()
    ...
```

==

# Data Collection

## Classification Embeddings (medium) 

```python
...
outputs = model(**tokens)[0].detach().numpy()
scores = 1 / (1 + np.exp(-outputs))  # Sigmoid
class_ids = np.argmax(scores, axis=1)
for i, class_id in enumerate(class_ids):
    results.append({"story_id": ids[i], "label" : model.config.id2label[class_id]})
...
```

===

# Data Selection

==

# Data Selection

## Stories

- Clip the first and last full year of stories. <!-- .element: class="fragment" -->
- Remove duplicate stories (big stories span multiple days). <!-- .element: class="fragment" -->

==
# Data Selection

## Publishers

- Combine subdomains of stories. <!-- .element: class="fragment" -->
    - blog.washingtonpost.com and washingtonpost.com are considered the same publisher. 
    - This could be bad. For example: opinion.wsj.com != wsj.com. 

==

# Data Selection

## Links

- Select only stories with publishers whose story had been a 'parent' ('original publishers'). <!-- .element: class="fragment" -->
    - Eliminates small blogs and non-original news.
- Eliminate publishers without links to original publishers. <!-- .element: class="fragment" -->
    - Eliminate silo'ed publications. 
    - Link matrix is square and low'ish dimensional. 

==

# Data Selection

## Bias

- Keep all ratings, even ones with low agree/disagree ratio.
- Join datasets on publisher name. 
    - Not automatic (look up Named Entity Recognition). <!-- .element: class="fragment" -->
    - Started with 'jaro winkler similarity' then manually from there.
- Use numeric values
    - [left: -2, left-center: -1, ...]

===

# Descriptive Stats

## Raw

| metric            |   value |
|:------------------|--------:|
| total stories     |  299714 |
| total related     |  960111 |
| publishers        |    7031 |
| authors           |   34346 |
| max year          |    2023 |
| min year          |    2005 |
| top level domains |    7063 |

==
# Descriptive Stats

## Stories Per Publisher

![stories per publisher](/static/577/stories_per_publisher.png)

==

# Descriptive Stats

## Top Publishers

![top publishers](https://studentweb.cs.wwu.edu/~jensen33/static/577/top_publishers.png)

==

# Descriptive Stats

## Articles Per Year

![articles per year](https://studentweb.cs.wwu.edu/~jensen33/static/577/articles_per_year.png)

==

# Descriptive Stats

## Common TLDs

![common tlds](https://studentweb.cs.wwu.edu/~jensen33/static/577/common_tld.png)

==

# Descriptive Stats

## Post Process

| metric            |   value |
|:------------------|--------:|
| total stories     |  251553 |
| total related     |  815183 |
| publishers        |     223 |
| authors           |   23809 |
| max year          |    2022 |
| min year          |    2006 |
| top level domains |     234 |

===

# Experiments

1. **clustering** on link similarity. <!-- .element: class="fragment" -->
2. **classification** on link similarity. <!-- .element: class="fragment" -->
3. **classification** on sentence embedding. <!-- .element: class="fragment" -->
4. **classification** on sentiment analysis. <!-- .element: class="fragment" -->
5. **regression** on emotional classification over time and publication. <!-- .element: class="fragment" -->

===

# Experiment 1

**clustering** on link similarity.

==

# Experiment 1

## Setup

- Create one-hot encoding of links between publishers. <!-- .element: class="fragment" -->
- Cluster the encoding. <!-- .element: class="fragment" -->
- Expect similar publications in same cluster. <!-- .element: class="fragment" -->
- Use PCA to visualize clusters. <!-- .element: class="fragment" -->

Note:
Principle Component Analysis: 
- a statistical technique for reducing the dimensionality of a dataset.
- linear transformation into a new coordinate system where (most of) the variation data can be described with fewer dimensions than the initial data.

==

# Experiment 1

## One Hot Encoding

| publisher |  nytimes|  wsj| newsweek|  ...|
|:----------|--------:|----:|--------:|----:|
| nytimes   |        1|    1|        1|  ...|
| wsj       |        1|    1|        0|  ...|
| newsweek  |        0|    0|        1|  ...|
| ...       |      ...|  ...|      ...|  ...|

==

# Experiment 1

## n-Hot Encoding

| publisher |  nytimes|  wsj| newsweek|  ...|
|:----------|--------:|----:|--------:|----:|
| nytimes   |       11|    1|      141|  ...|
| wsj       |        1|   31|        0|  ...|
| newsweek  |        0|    0|        1|  ...|
| ...       |      ...|  ...|      ...|  ...|

==

# Experiment 1

## Normalized n-Hot Encoding

| publisher |  nytimes|  wsj| newsweek|  ...|
|:----------|--------:|----:|--------:|----:|
| nytimes   |        0|  0.4|      0.2|  ...|
| wsj       |      0.2|    0|      0.4|  ...|
| newsweek  |      0.0|  0.0|      0.0|  ...|
| ...       |      ...|  ...|      ...|  ...|

==

# Experiment 1

## Elbow criterion

![elbow](https://studentweb.cs.wwu.edu/~jensen33/static/577/link_cluster_elbow.png)

Note:

The elbow method looks at the percentage of explained variance as a function of the number of clusters: 

One should choose a number of clusters so that adding another cluster doesn't give much better modeling of the data.

Percentage of variance explained is the ratio of the between-group variance to the total variance,

==

# Experiment 1

## Link Magnitude

![link magnitude cluster](https://studentweb.cs.wwu.edu/~jensen33/static/577/link_pca_clusters_links.png)

==

# Experiment 1

## Normalized

![link normalized cluster](https://studentweb.cs.wwu.edu/~jensen33/static/577/link_pca_clusters_normalized.png)

==

# Experiment 1

## One Hot

![link onehot cluster](https://studentweb.cs.wwu.edu/~jensen33/static/577/link_pca_clusters_onehot.png)

==

# Experiment 1

## Discussion

- Best encoding: One hot. <!-- .element: class="fragment" -->
- Clusters, but no explanation. <!-- .element: class="fragment" -->
- Limitation: need the link encoding to cluster. <!-- .element: class="fragment" -->
    - Smaller publishers might not link very much.
- TODO: Association Rule Mining. <!-- .element: class="fragment" -->

===

# Experiment 2

**classification** on link similarity.

==

# Experiment 2

## Setup

- **clustering**. <!-- .element: class="fragment" -->
- Create features. <!-- .element: class="fragment" -->:
    - Publisher frequency.
    - Reuse link encodings.
- Create classes: <!-- .element: class="fragment" -->
    - Join bias classifications.
- Train classifier. <!-- .element: class="fragment" -->

Note:

==
# Experiment 2

## Descriptive stats

| metric      | value     |
|:------------|:----------|
| publishers  | 1582      |
| labels      | 6         |
| left        | 482       |
| center      | 711       |
| right       | 369       |
| agree range | [0.0-1.0] |

==

# Experiment 2

## PCA + Labels

![pca vs. bias labels](https://studentweb.cs.wwu.edu/~jensen33/static/577/pca_with_classes.png)

==

# Experiment 2

## Discussion

- Link encodings (and their PCA) are useful. <!-- .element: class="fragment" -->
    - Labels are (sort of) separated and clustered.
    - Creating them for smaller publishers is trivial.
==

# Experiment 2

## Limitations

- Dependent on accurate rating. <!-- .element: class="fragment" -->
- Ordinal ratings not available. <!-- .element: class="fragment" -->
- Dependent on accurate joining across datasets. <!-- .element: class="fragment" -->
- Entire publication is rated, not authors. <!-- .element: class="fragment" -->
- Don't know what to do with community rating. <!-- .element: class="fragment" -->

===

# Experiment 3 

**classification** on sentence embedding.

==

# Experiment 3 

## Setup


- **classification**. <!-- .element: class="fragment" -->
- Generate sentence embedding for each title. <!-- .element: class="fragment" -->
- Rerun PCA analysis on title embeddings. <!-- .element: class="fragment" -->
- Use kNN classifier to map embedding features to bias rating. <!-- .element: class="fragment" -->

==

# Experiment 3

## Sentence Embeddings

1. Extract titles.
2. Tokenize titles.
3. Pick pretrained Language Model.
4. Generate embeddings from tokens.

==

# Experiment 3

## Tokens

**The sentence:**

"Spain, Land of 10 P.M. Dinners, Asks if It's Time to Reset Clock"

**Tokenizes to:**

```
['[CLS]', 'spain', ',', 'land', 'of', '10', 'p', '.', 'm', '.', 
    'dinners', ',', 'asks', 'if', 'it', "'", 's', 'time', 'to', 
    'reset', 'clock', '[SEP]']
```

Note:
[CLS] is unique to BERT models and stands for classification.

==

# Experiment 3

## Tokens

**The sentence:**

"NPR/PBS NewsHour/Marist Poll Results and Analysis"

**Tokenizes to:**

```
['[CLS]', 'npr', '/', 'pbs', 'news', '##ho', '##ur', '/', 'maris', 
    '##t', 'poll', 'results', 'and', 'analysis', '[SEP]', '[PAD]', 
    '[PAD]', '[PAD]', '[PAD]', '[PAD]', '[PAD]', '[PAD]']
```

Note:
The padding is there to make all tokenized vectors equal length.

The tokenizer also outputs a mask vector that the language model uses to ignore the padding.

==

# Experiment 3

## Embeddings

- Using a BERT (Bidirectional Encoder Representations from Transformers) based model.
- Input: tokens.
- Output: dense vectors representing 'semantic meaning' of tokens.

==

# Experiment 3

## Embeddings

**The tokens:**

```
['[CLS]', 'npr', '/', 'pbs', 'news', '##ho', '##ur', '/', 'maris', 
    '##t', 'poll', 'results', 'and', 'analysis', '[SEP]', '[PAD]', 
    '[PAD]', '[PAD]', '[PAD]', '[PAD]', '[PAD]', '[PAD]']
```

**Embeds to a vector (1, 384):**

```
array([[ 0.12444635, -0.05962477, -0.00127911, ...,  0.13943022,
        -0.2552534 , -0.00238779],
       [ 0.01535596, -0.05933844, -0.0099495 , ...,  0.48110735,
         0.1370568 ,  0.3285091 ],
       [ 0.2831368 , -0.4200529 ,  0.10879617, ...,  0.15663117,
        -0.29782432,  0.4289513 ],
       ...,
```
==

# Experiment 3

## Results

![pca vs. classes](https://studentweb.cs.wwu.edu/~jensen33/static/577/embedding_sentence_pca.png)

Note:
Not a lot of information in PCA this time.

==

# Experiment 3

## Results

![pca vs. avg embedding](https://studentweb.cs.wwu.edu/~jensen33/static/577/avg_embedding_sentence_pca.png) <!-- .element: class="r-stretch" -->


Note:
What about average publisher embedding?

==

# Experiment 3

## Results

![knn embedding confusion](https://studentweb.cs.wwu.edu/~jensen33/static/577/sentence_confusion.png)

Note:
Trained a kNN from sklearn.

Set aside 20% of the data as a test set.

Once trained, compared the predictions with the true on the test set.

==

# Experiment 3

## Discussion

- Embedding space is hard to condense with PCA. <!-- .element: class="fragment" -->
- Maybe the classifier is learning to guess 'left-ish'? <!-- .element: class="fragment" -->

===

# Experiment 4

**classification** on sentiment analysis.

==
# Experiment 4

## Setup

- Use pretrained Language Classifier. <!-- .element: class="fragment" -->
- Previously: Mapped twitter posts to tokens, to embedding, to ['positive', 'negative'] labels. <!-- .element: class="fragment" -->
- Predict: rate of neutral titles decreasing over time.

==

# Experiment 4

## Results

![sentiment over time](https://studentweb.cs.wwu.edu/~jensen33/static/577/sentiment_over_time.png)

==
# Experiment 4

## Results

![bias vs. sentiment over time](https://studentweb.cs.wwu.edu/~jensen33/static/577/bias_vs_sentiment_over_time.png)

==

# Experiment 4

## Discussion

-

===

# Experiment 5

**regression** on emotional classification over time and publication.

==
# Experiment 5

## Setup

- Use pretrained language classifier. <!-- .element: class="fragment" -->
- Previously: Mapped reddit posts to tokens, to embedding, to emotion labels. <!-- .element: class="fragment" -->
- Predict: rate of neutral titles decreasing over time.
- Classify: 
    - features: emotional labels
    - labels: bias

==

# Experiment 5

## Results

![emotion over time](https://studentweb.cs.wwu.edu/~jensen33/static/577/emotion_over_time.png)

==

# Experiment 5

## Results

![emotion regression time](https://studentweb.cs.wwu.edu/~jensen33/static/577/emotion_regression.png)

==

# Experiment 5

## Discussion

- Neutral story titles dominate the dataset. <!-- .element: class="fragment" -->
- Increase in stories published might explain most of the trend. <!-- .element: class="fragment" -->
- Far-right and far-left both became less neutral. <!-- .element: class="fragment" -->
- Left-Center and right-center became more emotional, but also neutral. <!-- .element: class="fragment" -->
- Not a lot of movement overall. <!-- .element: class="fragment" -->

===

# Experiment 6 (**TODO**)

## Setup

- Have a lot of features now. <!-- .element: class="fragment" -->
    - Link PCA components.
    - Embedding PCA components.
    - Sentiment.
    - Emotion.
- Can we predict with all of them: Bias. <!-- .element: class="fragment" -->
- End user: Is that useful? Where will I get all that at inference time? <!-- .element: class="fragment" -->

===

# Overall Limitations

- Many different authors under the same publisher. <!-- .element: class="fragment" -->
- Publishers use syndication. <!-- .element: class="fragment" -->
- Bias ratings are biased. <!-- .element: class="fragment" -->

===

# Questions

===

<!-- .section: id="references" -->

# References

[1]: Stewart, A.J. et al. 2020. Polarization under rising inequality and economic decline. Science Advances. 6, 50 (Dec. 2020), eabd4201. DOI:https://doi.org/10.1126/sciadv.abd4201.

Note: