We have been using jamovi as a trial at my university (first years stats, compulsory course; 400-ish students; all enrolled in health and science) alongside SPSS (hoping to ditch SPSS in the future).

My students do a free-choice project (with some boundaries) and one group measured ruler bending deflections for wooden and plastic rulers.

As part of their analysis, they were seeking a CI for the difference between the means of the two groups. The CI confused them: The CI given in jamovi is from -Inf to -60.1.

The reason is their choice of alternative hypothesis: as shown on their output (image attached), they used Ha Wooden < Plastic.

Changing the alternative hypothesis to the two-tailed alternative gives CI as -69.2 to -59.2 (so both limits have changed).

The same data in SPSS give -69.2 to -59.2, so the SPSS output agrees with jamovi's when the two-tailed alternative is selected. (Of course, SPSS always does two-tailed tests by default, at least in my experience.)

Now I see where jamovi is going here. But to get a CI for the difference between the means of the two groups, one has to select a two-tailed test, whether a two-tailed test is really what one wants to test for (ignoring all the discussion about deciding on one- or two-tailed tests and their merits...).

So my students want to obtain two things from jamovi:

- A CI for the difference between the means, when they need to set the alternative hypotheses as two-tailed
- A one-tailed test to compare the means, when they need to select a one-tailed alternative hypothesis.

To me this is very confusing for students, especially at this level.

Is this intentional? It seems to me to be a poor choice (IMHO)... Thoughts? Opinions?

P.