Constraints on age country random effects

[athowes]

Need to be added, as well as potentially age effects (not by country).

[athowes]

Looks like we got it:

> variance_df %>% select(starts_with("percentage"))
# A tibble: 1 × 5
  percentage_variance_cat_idx percentage_variance_age_idx percentage_variance_iso3_idx percentage_variance_… percentage_vari…
                        <dbl>                       <dbl>                        <dbl>                 <dbl>            <dbl>
1                      0.0146                       0.617                        0.217                 0.127           0.0244