Question on what is being repeated in this repeated measures ANOVA

Question

I am replicating a two-way repeated measures ANOVA in a journal for practice. There are:

• One dependent variable density (I chose one from multiple dv presented in journal)
• Fixed factor of drought (wet/dry year) Years
• Fixed factor of grazing (no/light/moderate intensity) Land_use

The data is collected from 10 plots for each grazing treatment for three months in each of the two years (wet/dry). The paper considered monthly observations as replications (thus 30 replicates per treatment), and integrated month as random factor.

Question: Is this a repeated measure because the drought factor was examined in the same plots (experience wet (2012) and then dry (2013))? Or is it because the dependent variable was measured in the same plot for three months (Jul-Sep for each grazing&drought pair)?

I don't think the latter is correct since month is considered as replications. But I saw from many websites that in repeated measures we compare more than two timepoints or conditions, whereas I only have two drought conditions.

Could someone clarify please? I am struggling ...

Answer 1

The repeated-measures tag description is your friend here:

Repeated measures data occur when more than one measurement is collected on the same unit (e.g. subject).

As multiple data values were collected from each of the plots of land, there are repeated measures on those plots. That's the key, as observations collected from the same plot are likely to be correlated across times and conditions. Analysis of repeated measures must take potential lack of independence within each plot of land into account, whether you have 2 or 20 treatments or time points.

The issues of what's considered replications of the same experimental time point/condition versus different time points/conditions have to do with the way that the modeling accounts for the repeated measures. But if you have more than one measurement on the same "unit" you have repeated measures.