Slopes of utterance length quartiles temporal regression lines.

<p>Slopes of utterance length quartiles temporal regression lines.</p

Multiple regression of median utterance length with US Census Bureau QuickFacts variables as possible predictors.

<p>Standard errors are presented in parentheses below the corresponding parameter estimates. Bold indicates significance at the 5% level, .</p>**<p>.</p>***<p>.</p

Utterance length distribution of the entire dataset.

<p><b>A.</b> Unfiltered utterance length distribution of the entire dataset <b>B.</b> Utterance length distribution of English tweets with URLs and LOL removed. The solid line in both plots is the best fit of Eq. (1).</p

Utterance length distribution over time.

<p>First quartile Q1 (square), median Q2 (circle) and third quartile Q3 (triangle) of the <b>A.</b> original dataset, <b>B.</b> after resampling into utterances per day, <b>C.</b> removing URLs and <b>D.</b> restricting to English tweets.</p

Representative utterance length distributions per year.

<p>Utterance length distribution of every first available Friday of December in the dataset.</p

Utterance lengths across US states.

<p><b>A.</b> Box plot of the utterance length distribution of each US state sorted by increasing median utterance length. The notches were estimated using 10,000 bootstrap repetitions but the resulting bootstrapped median values are the same as the empirical median values <b>B.</b> Contiguous US states colored with the bootstrapped median utterance length.</p

Exploring possible mechanisms of shortening.

<p>Annual values of <b>A.</b> median word length of all words, <b>B.</b> median word length of the 1000 most frequently occurring words, <b>C.</b> most frequent word length of the 1000 most frequently occurring words, <b>D.</b> fraction of 1000 most frequently occurring words relatively to all occurrences of words, <b>E.</b> median utterance length in number of words <b>F.</b> median tweet length in number of words, and <b>G.</b> median trending topic phrase length.</p

Slopes of utterance length quartiles temporal regression lines.

<p>Visualization of <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0077793#pone-0077793-t001" target="_blank">Table 1</a>.</p

Single-variable linear regression of median utterance length with selected US Census Bureau QuickFacts variables.

<p>Standard errors are presented in parentheses below the corresponding parameter estimates. Bold indicates significance at the 5% level, .</p>**<p>.</p>***<p>.</p

Median message length, in words, for different geographical regions after imposing user tweet count thresholds.

<p>Median message length, in words, for different geographical regions after imposing user tweet count thresholds.</p