Although the most common ribbing combinations are those that are even (that is, the rib uses the same number of knitted versus purl columns), the columns don't have to be even. Many attractive and functional ribs have wider knit columns than purl columns.
4 x 2 and 2 x 4 ribbing
There's no reason to keep knit ribs and purl ribs the same number of stitches. You can work ribs in uneven combinations, such as 4 x 2, 2 x 4, and so on. To create 4 x 2 ribbing:
Cast on a multiple of 6 sts, plus 4 sts. (You can work this pattern over a multiple of 6 stitches, but it won't be symmetrical.)
Row 1: * K4, p2; rep from * to last 4 sts, k4.
Row 2: * P4, k2; rep from * to last 4 sts, p4.
Rep Rows 1 and 2 for pattern.
If you turn this swatch over, you'll have a very different looking pattern — thin vertical stripes instead of thick ones.