How One Choice Burned the New Period-Spacing Study

Every once in a while, a study is published that that seems to catch fire. Whether it adds to an existing debate or sparks a new one, it somehow seems to resonate with an issue that some may not have been aware even existed. One such article was recently published in Attention, Perception, & Psychophysics by a group of researchers from Skidmore College. Its premise- at the end of a sentence, two spaces after the period may be better than one.

While this may not be earth-shattering to you, it is for some. In fact, the period-space conundrum is quite vehemently debated among many journalists and typographers. The study, headed by Dr. Rebecca Johnson, recruited 60 college students to read several paragraphs, which used either the one-space or two-space convention. Johnson and her colleagues assessed the time it took students to read, as well as the reading comprehension of each paragraph. They also used an eye-tracker to examine how the students read the ends of each sentence (consisting of the punctuation mark as well as the word immediately preceding and following it), acquiring measures such as fixation time, probability of skipping the section, and likelihood of going back to it later. They found that participants who use two spaces when they type read the two-spaced paragraphs about 3% faster than one-spaced paragraphs. For all students, reading comprehension was the same for both styles of typing. Eye-tracking also revealed that all students fixated on the sentence-ends less for two-space paragraphs and skipped over the sections more. While this finding does not seem to be extraordinarily meaningful, given the available global speed measure, the researchers suggest that the eye-tacking may provide a sign that the stimuli needed to consist of more text for the reading-speed effects to become more apparent.

The article was quickly touted as a decisive blow to the one-space camp- science had finally made up its mind. Then, almost as quickly, it was torn to shreds by all sorts of bloggers and journalists. The criticisms are completely valid. The effect sizes were small and very specific. The student-based population made results difficult to generalize. In any subject, one study only proves so much. Yet, the most damning critique was perhaps that the researchers used a monospaced font for all of the stimulus paragraphs. That means the letters are all allotted the same width, as opposed to having a variable width, like essentially all modern fonts. Though this seems small, it is essential to the debate, since the argument in favor of one space after a period is largely based off the idea that modern fonts, with their variable widths, are designed to look best with one space after the period. Monospace fonts were only ever really used back when the typewriter was king, and that spacing was one of the main reasons why typists followed the two-space rule- otherwise, everything just seemed to blend together. Johnson defended her choice by explaining that most eye-tracking studies of this nature used a monospace font. Indeed, it is a boon when attempting to quantify how people read each sentence, since its consistency makes the study much more resistant to confounds brought about by the structure of different words. Yet, regardless, this does not overturn the fact that the choice left a glaring hole in the study’s applicability.

This leads into my main point. When we strip away the context, what we find is a classic research problem- does one emphasize internal or external validity? Internal validity can be defined as how well a study measures what it means to measure. Are there confounds that influence the data in ways that are not related to the topic of interest? Are the measuring tools accurate and used in the correct context? External validity refers to how well a study relates to the real world. Once you take the findings out of the lab setting and into the much more complicated environment of real life, do they still apply? Obviously, both are important, but any experienced researcher will know that one often has to make a choice that partially sacrifices one for the sake of the other. For the more you try to control a study, the less like real-life it often becomes. So, assuming (just for sake of argument) that we do not live in a perfect, fantast world where all of our dreams come true, researchers have to be able to discern when to emphasize each type of validity. Johnson emphasized internal validity over external validity, but because the subject of that choice was central to the one-space vs two-space argument, the article ended up getting burned. Arguably, if she had chosen a more modern font, the loss of internal validity would not have been nearly as detrimental.

This choice is often emphasized in market research. Marketers don’t want to know how people will react in a lab. Their business depends on how people respond in real life. Thus, many market research studies tend to skew toward being more externally valid. While this is extremely important, it is also imperative to remember that a certain amount of internal validity is needed to be able to conclude anything meaningful at all. It takes an experienced researcher to walk the validity tightrope, which is why any good researcher will let their client know if the protocol skews too far from either standard. At the end of the day, every choice counts, and even small details can throw this balance off. And when the study can potentially save a company millions of dollars, their researcher really has no room to space.

The article in question

Johnson, R. L., Bui, B., & Schmitt, L. L. (2018). Are two spaces better than one? The effect of spacing following periods and commas during reading. Attention, Perception, & Psychophysics, 1-8.