Merge branch 'develop'

Author: MichaelRoeder

README.md

@@ -14,6 +14,14 @@ Please take a look at the the wikipage to read <a href="https://github.com/AKSW/
 
 If you are using Palmetto for an experiment or something similar that leads to a publication, please cite the paper "Exploring the Space of Topic Coherence Measures" that you can find on the project website. A link to the project website is welcome as well :)
 
+### Applicability
+
+The coherence measures implemented with Palmetto mainly built on a reference index. This index is used to derive counts for the calculation of the coehrence values. These values can be used to measure the human interpretability of topics based on the topics' top words. It should be noted that the preprocessing of the index has an influence on the results. 
+
+_It is highly suggested to use an index that fits to the preprocessing that has been applied to the corpus on which the topics have been generated._
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+We use an English Wikipedia which has been preprocessed using a Lemmatizer. In practice, this means that word groups with non-lemmatized words may lead to unintuitive results simply because these word forms are underrepresented or even missing in our index (e.g., #57). In these cases, it is recommended to [generate an own index](https://github.com/dice-group/Palmetto/wiki/How-to-create-a-new-index).
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 ### Directories
 
 The `palmetto` directory contains the Palmetto library.