Burrows’ Zeta#

Burrows’ Zeta is a method for using the frequencies of mid-range words for a classification exercise. We take a Text Set of Class A samples and a Text Set of Class B samples. Which words which are used regularly in Class A and rarely in Class B, and vice-versa? Each sample in the analysis is then given two scores, based on how many of the words in the two lists occur in it. A mystery sample which has many of the Class A words in its vocabulary and rather few of the Class B words can be assigned to Class A.

An example of how you might use Burrows’ Zeta is to solve an authorship problem. A new version of The Spanish Tragedy was published in 1602 with some added scenes. There is some evidence to connect them with Ben Jonson, but many commentators think they sound Shakespearean. We take a set of Shakespeare plays as Class A, and a set of Jonson plays as Class B, find the Class A words and the Class B words with the highest Zeta index scores, and see how many from each list are in the added scenes. How Shakespearean is the vocabulary of the added scenes, and alternatively how Jonsonian is it?

Platform Process#

  1. From the home page, select Burrows’ Zeta.

  2. Select Text Sets to Add for Experiment.

  3. Click Edit next to a Text Set to change its analysis criteria. Apply the following settings as required:

Segmentation Options

  • Segment by Tag – This option is usually for Text Sets that include XML files that have been segmented as markup. ‘Tag’ refers to markup tags in XML that delineate a section of the text, e.g. ‘Act’. Type tags into this field to separate the Text Set into blocks divided by those tags.

  • Block Method – Defines the method for creating blocks:

    • BlockBigLast – Assign any words left over from creating blocks to the last block, creating one large end block.

    • BlockSmallLast – Assign any words left over from creating blocks to their own block, creating one small end block.

    • OverlappingBigLast – Create blocks that overlap with each other. Any words that are left over from creating blocks are assigned to the last block, creating one large end block.

    • OverlappingSmallLast – Create blocks that overlap with each other. Any words that are left over from creating blocks are assigned to their own block, creating one small end block.

    • Text – Use the entirety of the Texts in the Text Set as single blocks.

  • Block Size – Set the number of words to include in a block.

  • Advancement Size – For overlapping blocks, denote the starting point of the next block, i.e. an advancement size of 100 would mean that each block starts 100 words after the start of the previous block.

Word Selection Criteria – Fill in the fields to define how words are selected in the Text Set.

Test Segments

  • Extract random test segments from this text set – Check this box and set a Test segment proportion to extract random segments to test. The extracted segments play no part in the selection of the words for the analysis so are a genuine test of the method where it is confronted with freshly introduced samples.

  • Zeta Index Calculation

  1. Apply the following settings as required:

General#

Zeta Parameters

  • Output Size – Set the number of Zeta Words that you want to include in the results.

  • Minimum Zeta score to output – In the Zeta procedure each word is given a Zeta index score. This setting allows you to set a cut-off Zeta score, rather than a cut-off number of words to include.

  • Random seed for test segment extraction – Once you have set a random seed, you will be able to return to the same random selection by entering the same seed next time. (Otherwise there is a separate random selection each time.)

  • Words – Type words into this field to specify words to include or hide in the results, depending on the dropdown above.

NGrams

  • Number of NGrams – Define the value of N for the NGram you want to analyse.

What is an NGram? An NGram refers to a number of words in a sequence. An NGram of 1 can be called a 1Gram, and refers to a single word. A 5Gram is a sequence of 5 words, like “how is it with you” or “get thee to a nunnery”.

Inclusions/Exclusions#

Select XML tags to include or exclude in the results.

Words to Exclude from Process – Type words into this field to completely exclude from the Burrows’ Zeta process. By default, we exclude punctuation.

  • Include Homograph Forms – Check this box to separate homograph forms of a word in the results (e.g. separate the noun and verb forms of “will”).

  1. Click Show Results to see the results on the right.

Interpret the Results#

Burrows’ Zeta results are split into a few tabs.

  • Zeta Experiment Summary – This view lists the Zeta Words that have been analysed. Use the dropdown to see the Hits, Frequencies, and Proportions of each Zeta Word in each Text Set, as well as in any random test segments. Hits gives the numbers of segments that include one or more instances of the word, Frequencies gives the total of the instances of the word, and Proportions gives the total of the instances as a percentage of the size of the block.

  • Text Sets – Each Text Set has its own result view, where you can see the frequencies of each Zeta Word in each segment/block of the Text Set. If you chose to extract random test segments from a Text Set, that will have its own tab as well.

Click Copy to Clipboard to copy the results so you can paste them into a document or spreadsheet.

API Process#