How to increase INTEGER for each checkbox marked?

For each box a User checks off, how can we add +1 to t.integer :missed?

Currently,

The index shows <%= habit.missed %>.

The form <%= f.check_box :missed %>. Should I use f.collection_check_boxes instead?

The model

scope :missed, -> { where(missed: 1) }
scope :nonmissed, -> { where(missed: 0) }

I couldn't get it to work with scope.

Right now even if a User clicks on the :missed checkbox the integer still shows up as 0 in the index (this is because the checkmark isn't saving upon submitting).

How can we make this work with 15 checkboxes in the _form?

Thank you in advance =]