How can I Interpret the slope of year variable?

Question

I was trying to model the relationship between time and mean egg laying dates across multiple farms.

lmer(mean_egg_dates ~ scale (Years) + (1|region), 
                    data = DF)

The time period was 60 years (1930-1990), and slope which I got was 32 for this model. Can I interpret it as a laying date shift of approximately 0.5 days/year (32/60) (which is sensible), OR should the output be interpreted as 32 days/year, which does not make any sense?.

Please advise.

Thanks

Rahul

Answer 1

It is clearly 0.5 days/year, because the 32-day shift occurred over a 60 year period. If you think this is an average hiding a sharper increase happening over a shorter period of time (in the extreme, the entire 32-day shift happing from, say, 1935 to 1936), then you should compute the slope over different smaller time periods.