Two conditions, counterbalanced

Duplicate the control line

Make the control condition first. Then duplicate its chamberline, so that the two lines start the same.

Give the copy a name that tells what it changes.

Change the one thing that differs

Open the chamber of the copy. Change only the manipulation. Here, this is one sentence in the briefing.

All other items stay the same as in the original. Thus a difference in the data comes from that sentence.

Define a counterbalanced condition variable

In Variables, add a counterbalance variable with one value for each condition.

The default strategy is Randomized blocks. Each block uses each value one time, in a random order. Thus the groups stay balanced, also when participants leave the study.

Assign lines by the variable

In the experiment settings, open Chamberline Assignment:

• Set Assignment Method to Variables-based.
• Select the variable.
• Add a rule for each value, with the name of its line.

Deploy to save.

Check that conditions stay apart

Open the link in two windows. The first participant gets one condition and the second participant gets the other condition.

Matching puts participants in groups only in the same chamberline. Thus conditions with shared chat rooms never mix. A condition waits for sufficient participants of its own. It does not use participants from the other condition.