Table 1.

Design table.

Question and hypotheses			Sampling plan (eg, power analysis)a		Analysis plana		Interpretation given to different outcomes
Does the Contain COVID Anxiety SSIb decrease generalized anxiety symptoms from baseline to 2 weeks later more than the placebo SSI Remain COVID Free?
	H1: Generalized anxiety decreases more when participants are randomized to the Contain COVID Anxiety SSI than when participants are randomized to the Remain COVID Free placebo SSI.	H1: n=400 for 95% power		H1: Test for assumptions and apply transformations as necessary. Take the 2-week follow-up generalized anxiety mean and enter it as the dependent variable in a linear model with the baseline generalized anxiety mean and treatment condition as predictors.		Support for H1: If the P value for condition is <.0167 in the H1 linear model and the 95% CI for the difference in generalized anxiety is negative and does not include 0 when participants are randomized to the Contain COVID Anxiety SSI, we will reject H0 and interpret the study as supporting Contain COVID Anxiety decreasing generalized anxiety more than the placebo SSI Remain COVID Free. Lack of support for H1: If the P value for the equivalence test described in the “Support for H0” section is >.0167, we will interpret the study as producing evidence that the Contain COVID Anxiety SSI is neither superior nor equivalent or inferior to the Remain COVID Free SSI at decreasing generalized anxiety.
	H0: Generalized anxiety either does not increase more when participants are randomized to the Contain COVID Anxiety SSI than when participants are randomized to the Remain COVID Free placebo SSI, or generalized anxiety increases more when participants are randomized to the Remain COVID Free placebo SSI than when participants are randomized to the Contain COVID Anxiety placebo SSI.	H0: n=150 for 95% power		H0: Test for assumptions and apply transformations as necessary. Take the 2 weeks later generalized anxiety mean and predict it with the baseline generalized anxiety mean. Enter the mean and SD of the standardized residuals from that model for when the condition is Remain COVID Free and the mean and SD of the standardized residuals from that model when the condition is Contain COVID Anxiety into a between-groups equivalence test with equivalence bounds of d=–0.66 to d=0.33.		Support for H0: If the P value for condition is <.0167 in the H1 linear model and the 95% CI for the difference in generalized anxiety is positive and does not include 0 when participants are randomized to the Remain COVID Free SSI or the P value or intervention order is >.0167 in the H1 linear model, we will run the between-groups equivalence test described in the analytic plan for H0. If the equivalence test has a P value <.0167, we will interpret the results as indicating the Contain COVID Anxiety SSI was equivalent or inferior to the Remain COVID Free SSI at improving generalized anxiety. Lack of support for H0: If the P value for the equivalence test described in the “Support for H0” section is >.0167, we will interpret the study as producing evidence that the Contain COVID Anxiety SSI is neither superior nor equivalent or inferior to the Remain COVID Free SSI at decreasing generalized anxiety.
Does the Contain COVID Anxiety SSI increase perceived control over anxiety from baseline to immediately post-SSI more than the placebo SSI Remain COVID Free?
	H1: Perceived control over anxiety increases more when participants are randomized to the Contain COVID Anxiety SSI than when participants are randomized to the Remain COVID Free placebo SSI.	H1: n=350 for 95% power		H1: Test for assumptions and apply transformations as necessary. Take the post-SSI perceived control over anxiety mean and enter it as the dependent variable in a linear model with baseline perceived control over anxiety mean and treatment condition as predictors.		Support for H1: If the P value for condition is <.0167 in the H1 linear model and the 95% CI for the difference in perceived control over anxiety is positive and does not include 0 when participants are randomized to the Contain COVID Anxiety SSI, we will reject H0 and interpret the study as supporting Contain COVID Anxiety increasing perceived control over anxiety more than the placebo SSI Remain COVID Free. Lack of support for H1: If the P value for the equivalence test described in the “Support for H0” section is >.0167, we will interpret the study as producing evidence that the Contain COVID Anxiety SSI is neither superior nor equivalent or inferior to the Remain COVID Free SSI at improving perceived control over anxiety.
	H0: Perceived control over anxiety either does not increase more when participants are randomized to the Contain COVID Anxiety SSI than when participants are randomized to the Remain COVID Free placebo SSI or perceived control over anxiety increases more when participants are randomized to the Remain COVID Free placebo SSI than when participants are randomized to the Contain COVID Anxiety placebo SSI.	H0: n=150 for 95% power		H0: Test for assumptions and apply transformations as necessary. Take the post-SSI perceived control over anxiety mean and predict it with the baseline perceived control over anxiety mean. Enter the mean and SD of the standardized residuals from that model for when the condition is Remain COVID Free and the mean and SD of the standardized residuals from that model when the intervention order is Contain COVID Anxiety into a between groups equivalence test with equivalence bounds of d=–0.63 to d=0.21.		Support for H0: If the P value for condition is <.0167 in the H1 linear model and the 95% CI for the difference in perceived control over anxiety is negative and does not include 0 when participants are randomized to the Remain COVID Free SSI or the P value or intervention order is >.0167 in the H1 linear model, we will run the between-groups equivalence test described in the analytic plan for H0. If the equivalence test has a P value <.0167, we will interpret the results as indicating the Contain COVID Anxiety SSI was equivalent or inferior to the Remain COVID Free SSI at improving perceived control over anxiety. Lack of support for H0: If the P value for the equivalence test described in the “Support for H0” section is >.0167, we will interpret the study as producing evidence that the Contain COVID Anxiety SSI is neither superior nor equivalent or inferior to the Remain COVID Free SSI at improving perceived control over anxiety.
Does completing the Contain COVID Anxiety SSI have an association with social distancing intentions statistically equivalent to 0?
	H1: Social distancing intentions do not increase or decrease pre-Contain COVID Anxiety SSIs to immediate post-Contain COVID Anxiety SSI.	H1: n=154 for 95% power		H1: Test for assumptions and apply transformations as necessary. Enter the mean and SD of the social distancing intention composites at baseline and post-Contain COVID Anxiety SSI (only among people who were randomized to the Contain COVID Anxiety) into a paired equivalence test with equivalence bounds of d=–0.33 to d=0.33.		Support for H1: The P value for the paired equivalence test described in the analysis plan column is <.0167. We will interpret this result as support for the hypothesis that social distancing intentions are not increased or decreased pre to post both Contain COVID Anxiety (even if the paired t test for H0 in the analysis plan column also has a P value <.0167).
	H0: Social distancing intentions either increase or decrease pre- to immediate post-Contain COVID Anxiety SSI	H0: n=156 for 95% power		H0: Test for assumptions and apply transformations as necessary. Enter the mean and SD of the social distancing intention composites at baseline and post-Contain COVID Anxiety SSI (only among people who were randomized to the Contain COVID Anxiety) into a paired t test.		Support for H0: The P value for the paired equivalence test in the analysis plan column is >.0167, and the P value for the paired t test in the analysis plan column is <.0167. We will interpret this result as supporting the hypothesis that social distancing intentions either increased or decreased as the result of completing the Contain COVID Anxiety SSI. We will examine the direction of the effect by looking at the direction of the effect size (positive effect size = increase in social distancing intentions; negative effect size = decrease in social distancing intentions).

^aRefer to the R code on the open science framework page for the power analysis and analysis plan [52].

^bSSI: single-session intervention.