A famous example of a significant absence is the the dog that didn’t bark in the night in the Sherlock Holmes story Silver Blaze. Holmes correctly spots that the absence of reaction from the dog is significant, and indicates that the crime was an inside job.
A classic example of as significant absence from research is the Michelson-Morley experiment in 1887. The researchers set out to measure the speed at which the earth moved through ‘luminiferous ether’. They found a significant absence of any evidence of movement (and of luminiferous ether). This was a complete surprise and sparked a massive flowering of new ideas in physics, the most prominent of which was Einstein’s theory of relativity.
On the social and political front, there are numerous significant absences in the media, literature, history books, and in most forms of high culture. Minority groups, for instance, are often significantly absent from these domains. So are social taboos; sex, for example, is a significant feature of human life, but there’s a significant absence of departments of sexual studies in universities.
Another more specific example is the concept of silence ownership. This concept comes from the field of discourse analysis. As the name implies, this involves analysing discourse such as conversations between people.
One of the things you find when you analyse conversations systematically is that people take turns in a conversation. This in itself is no great surprise. However, the turn-taking includes some less obvious conventions about what happens during a silence. Some silences are treated as pauses, where the person who has been speaking is temporarily silent; other silences are treated as endings, when the speaker has finished speaking. If you start talking during a pause, that’s generally perceived as rude, whereas if you start talking after an ending, that’s acceptable. So, the silence during a pause belongs to the person who has been speaking. It’s a neat example of how there can be different types of silence, and different types of absence.
A major issue in content analysis is the things that aren’t mentioned in the text. You’ll need to decide which things to treat as significant absences and which to treat as non-significant absences.
Some absences are because of Taken For Granted or Not Worth Mentioning assumptions; the person has assumed that those points were so obvious that there was no need to mention them (for instance, the assumption that a product shouldn’t kill someone using it).
Other absences are because of taboos; for instance, if you did a content analysis of classic 1950s Westerns, you’d find few or no mentions of people using the toilet.
Some absences are just because of chance. Say you select a batch of texts that happen not to include mentions of a particular topic, but that topic is mentioned in similar texts outside your sample. This is most likely to occur with topics that are relatively rare; you need to be sure your sampling process can detect whether mentions of that topic are at the level that would be expected by chance.