StoryArcs

Galvanize Data Science Capstone Project

Demetria McAleer

Story shapes

• The emotional ups and downs of every story form its shape.

• We can plot these shapes using sentiment analysis, specifically polarity (a measure of how positive or negative the words are in a given window of the story).

• The purpose of this project is to see what we can learn about how stories work by analyzing their shapes.

Creating story shapes

• I web-scraped about 1100 movie scripts from the Internet Movie Script Database.

• Then, I split each script into equal sized windows, and for each window, took the mean polarity score using TextBlob.

• Now, each movie is represented at a vector of the sentiments at each point in the movie.

• When you plot all the movie scripts together, you get... story shape spaghetti, like so:

Clusters

• My next step was to use K-means clustering to group common story shapes together. But a problem immediately emerged...

Change in sentiment vs. absolute sentiment

• Because some movies just are happier or sadder than others, movies wind up clustered on their overall average sentiment rather than the actual shape of the story.

• For this reason, at this point I switch to representing each story as a vector of the differences between the sentiments at each point, rather than the absolute sentiment.

Clusters, but actually working this time

• Using K-means, four distinct clusters of movies occur.

• Why four clusters, you might ask? Whenever I chose a number higher than four, the clusters would overlay each other - essentially, wanting to form four clusters even when I tried higher numbers.

• It's fun to see which movies fall into each cluster! For example, the green cluster that goes sad-happy-sad is Star Wars: The Empire Strikes Back, and the yellow cluster that has some ups and downs but ends happy is Star Wars: Return of the Jedi.

But what do the clusters mean?

• Because I used unsupervised learning to form the clusters, I was worried that they weren't "real" - that is, I was only seeing this shapes because I had told the algorithm to cluster, rather than because all the stories in each cluster actually had something in common.

• So, I started trying to tie the clusters to observable characteristics of the movies.

• Results were... mixed.

• Two of the clusters had a statistically significant relationship with box office revenues, two didn't.

• There were patterns in which clusters tended to have more of each genre (for example, many romances follow the yellow shape). But overall, a chi-squared test on genre and clusters was only marginally statistically significant.

• Overall, results were not as strong as I had hoped for. Time to keep thinking!

What are story shapes telling us?

• Stories tend to follow up-and-down patterns. We do not see any movies that are flat, or even always trending up or always trending down. Every movie has a mix.

• But the shapes of these patterns are largely unrelated to popularity (as measured by box office) or content (as measured by genre).

• However, sentiment in one part of the story does seem to be correlated with sentiment in other parts of the story. What else might we be able to do with that?

Ending prediction!

• For this part of the analysis, I remove the ending of the story (approximately the final 20%), and use the pattern of sentiment change (i.e. story shape) in the first 80% to predict the ending.

• The dependent variable is binary: happy (1) or sad (0).

• Again, it looks at change in sentiment at the end rather than absolute sentiment. (That is, a movie can be fairly bleak, but if it takes an upturn at the end, it counts as a happy ending.)

• Classes are relatively balanced (about 55% of movies turn upward at the end).

• Tried both Random Forest and Gradient Boosting model, but performance was similar. Final analysis refers to Random Forest.

Results

• Baseline models that either always predict a happy ending or predict a happy ending 55% of the time have relatively poor performance in both accuracy and F1 score.

• Adding other features of the movie such as box office, genre, and release year improve model performance to accuracy in the high 50s and F1 in the low 60s.

• Finally, adding sentiment from the first 80% of the movie bring both accuracy and F1 up to 70%.

• I think this is a cool result! It means that we don't have to know anything about the substantive content of a story - just the story's mood - to make a pretty good prediction about how the story is going to end.