The question is an important one, and perhaps one that we don't tend to think about so much as songwriters. What happens when we practice conscious lyric and melody writing as opposed to just letting a particular emotion or feeling flow. I will sit down sometimes with the conscious approach, meaning that I have made a decision on a particular day to write a song that is as far away from a cliched love song for instance... or a decidedly positive song because the last two were negative ones. We can thusly affect the percentage of positive to negative. It might seem counter productive as a song writing approach which some might say should be born entirely out of emotion, but for me a forced song is good exercise. This approach expands my options. To answer the question, I would say that I write about 50/50 positive to negative.