Observed (O) and expected (E) frequencies under the independence hypothesis considering risk factors.

<p>Observed (O) and expected (E) frequencies under the independence hypothesis considering risk factors.</p

Pearson's chi-square tests, corrected chi-square tests and logistic regressions for the search of viruses' interactions.

<p>Pearson's chi-square tests, corrected chi-square tests and logistic regressions for the search of viruses' interactions.</p

Robustness of the two approaches.

<p>Type I error (%) for the logistic regressions approach (blue empty points) and the corrected chi-square test (red full points) depending on the ratio of the number of factors to the sample size (N_F/n), considering three scenarios: i) all factors are qualitative (A); ii) all factors are quantitative (B) and iii) half of the factors are quantitative and the other half are qualitative (C). The type I error of the corrected chi-square tests represented here is based on P-value2 but similar results were observed with P-value1 (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0029618#pone.0029618.s003" target="_blank">Fig. S3</a>). Note that for the logistic regression approach, points resulting from a given sample size were linked to see the effect of the N_F/n ratio for different sample sizes (solid line: n = 100, dashed line: n = 200, dotted line: n = 300). The dashed horizontal line represents a type I error of 5%.</p