Lots of discussion around the blogosophere about polling yesterday. One thing that struck me is that political bloggers like to present polls as time-series data going back to before the last election while the mainstream media outlets that pay for all this data present them as cross-sectional, and generally only compare them to the previous poll that they conducted. Why is that? In my experience people like to be able to look at ‘the big picture’ and see the trends. TVNZ (for example) has conducted fourteen polls since the 2011 election. They’ve spent a load of money on them: why not throw that all up on the screen instead of just comparing the new poll to the one before it?