Introduction

To speed up screening for your systematic reviews, Covidence provides highlighting to help draw your eye to keywords in a study's title and abstract. You can set highlights for inclusion and exclusion keywords, to quickly determine whether a study is worth reviewing further.

This article covers how our highlighting strategies work, because it's a surprisingly tricky problem to solve. We'll also explain what might be happening if the highlights aren't working as you expect them to, and how we might be able to fix that for you.

If you'd like to read more about how to use highlights in your review, check out How to create and manage keyword and phrase highlights.

 

Approaches to highlighting

We take two approaches to highlighting in Covidence, one for highlighting a phrase, and one for highlighting
a single word.

Highlighting phrases

When highlighting phrases we highlight the entire phase for you without worrying about capitalization.
If you add "Mental Health" to your highlights, it will highlight "Mental Health", "Mental health",
"mental health" etc.

Highlighting single words

When highlighting single words, we apply a process called stemming. When stemming a word, we work out the room "stem" of that word is and then highlight any words that have that stem. The goal of this is to prevent you from needing to add lots of similar single-word highlights.

For example, say you add a single word highlight for "psychological". The stem of this word is "psycholog", so we will highlight "psychological", "psychology", "psychologies" etc.

 

Limits and exceptions

Word length

Words must be at least three characters long to be highlighted. For example, it is not possible to highlight the words "an" or "ex". This is to prevent over-zealous highlighting of your studies!

Words that produce aggressive highlights

Sometimes, stemming doesn't work the way we want it to and stemming is too aggressive. For example, the word "men" is a common prefix to lots of English words. If we applied stem highlighting to "men" we'd be highlighting "Mental", "Menstrual", "Meningitis", "Menopausal" and more all in the same review. This is too broad to be useful, so for words like this we turn stemming off and return to highlighting exact matches.

Prefixes that produce aggressive highlights

We also don't apply stemming to words when the stem produced is a common word prefix. For example, we don't stem anything that reduces down to "immun". Otherwise we'd be highlighting "immunization" and "immunosuppression" at the same time, and this produces a lot of false positives.

Something looks wrong?

We have to add each of these exceptions to our list, and we might have missed some along the way - if something doesn't look right to you, reach out to our support team!