13  Extend the heading rule

In forest_plot(), set heading.rule = TRUE to add a horizontal rule below the column headings for each panel. By default, it will extend to the width of the columns either side of each panel.

forest_plot(list("Observational" = my_resultsA,
                 "Genetic"       = my_resultsB),
            col.key    = "subgroup",
            row.labels = row_labels,
            heading.rule = TRUE)

Use unit() to set how far each rule should extended beyond the plotting area.

forest_plot(list("Observational" = my_resultsA,
                 "Genetic"       = my_resultsB),
            col.key    = "subgroup",
            row.labels = row_labels,
            heading.rule = unit(5, "mm"))

Use a unit() of length 2 to set the left and right extensions. They will be the same for all panels. By increasing the extension to the left, the appearance of a single rule across the row labels and all panels can be created.

forest_plot(list("Observational" = my_resultsA,
                 "Genetic"       = my_resultsB),
            col.key    = "subgroup",
            row.labels = row_labels,
            heading.rule = unit(c(22, 26.5), "mm"))