Shorter versus Longer Sentences


We recently had a question from a participant in our online course, "Technical Writing." As you may know. participants in all of our online courses receive feedback on their writing, and I'd shown her how to combine sentences to better illustrate the relationship between two sentences. She works in the financial industry which, as we all know, produces some difficult to read and understand documents (at least for many laypeople, me being one!). So, her question was whether, because the information she relays is often very complex, if she should rely more on shorter or longer sentences. A very good question indeed.
Are shorter sentences always easier to read?
Many of the professionals we work with, regardless of the industry, tend to believe that all information should be relayed in shorter, rather than longer, sentences. The idea for many of them is that shorter equals conciseness and succinctness (and they always seem to want to avoid the dreaded run-on sentence; that the run-on sentence does not mean a long sentence is a discussion for another day). The reality, however, is that shorter sentences do not necessarily enhance reading and may, in fact, prevent readers from understanding how ideas are related. Consider as well that shorter sentences may be so tedious that readers get frustrated and abandon the document altogether.
Consider these two fictional examples
Original: We went to the meeting in San Francisco. The notes from the meeting are attached. The names of those who attended are also attached.
Rewrite: Attached are the meeting notes and the names of attendees from the meeting in San Francisco.
Admittedly, this is not a complex example; the point, however, is that original is so tedious and reads more like first-grade primer than a sentence written by a professional (which may affect the writer's image). The point is that we can easily combine the ideas into one sentence and make it much less cumbersome to read. But the question remains: when do we use shorter or longer sentences? The idea behind choosing between a longer or shorter sentence is based on any number of parameters (who your readers are, what they know, and the purpose of the document, among other things), but is clearly linked to what we know about readers and how they read. Readability studies tell us that readers pay closer attention to shorter, rather than longer, sentences; at first blush, many writers think, "Yes! I was right! I should write in short sentences all the time." But if we carefully analyze this, we understand that this is not telling us to use short sentences all the time, but to reserve them for the most impactful information. Otherwise, we should be using longer, more complex sentences.
What's "impactful" information?
The question then becomes what we mean by impactful. Whether an idea is impactful depends in large part on, you guessed it, the parameters I set out earlier: audience, purpose, etc. In a nutshell, however, if an idea is easy for our readers to understand, a longer sentence is fine; however, if the idea is complex, then a shorter sentence would make more sense. What readability studies tell us about how readers read is useful, but is not "one size fits all"; we have to understand the readers of the documents our organization or industry produces and how they read and make sense of information. 
The point is this: think critically about your document, understand your readers and how they read, and define your purpose to determine when and how to use longer and shorter sentences.