You can show in 3 different plots:

- the data from this year

- the data from last year

- the differences between this year and last year

Alternatively, you can make a 2D scatter plot showing this year's data on the Y-axis and last year's data on the X-axis, while using different symbols/colors to indicate the treatment groups.

Alternatively, you can show the difference between the two years against the mean of the two years (it's called a "mean difference plot"), again indication the three treatment groups by different symbols/colors (looks like a rotated & scaled version of the 2D scatterplot from above).

@Jochem have well answered but I just want to inquire further mean difference plot. What is the base statistics behind it? Which software is best for it?

Jochen Wilhelm Thank you for your answer, and thanks for explaining it very clearly also!

Would you think that a scatter plot with all 3 treatment groups is best, or a single scatter plot for each treatment? I want to display as clearly as possible.

Also, I know you have suggested many plots, do you think this is better than having tables indicating the significant differences?

The mean difference plot, is this a bland altman?

Thanks so much, when it comes to stats i am better at the descriptive part rather than the visuals!

Kind regards

a) I think that's a matter of taste. If the plot look too busy, simplify it. Otherweise, keep the information together, so that the reader gets a comprehensive overview.

b) yes, it's also called a Bland-Altman plot

Jochen Wilhelm amazing, thanks you've been a big help :)