The PICO framework was originally developed in 1995. It was designed to facilitate research into clinical questions on the efficacy of interventions.
Over time this popular framework has been modified for use with questions with additional factors, such as types of studies. Variants include PICO, PICOS, PICOT, PICOTS, PICOTT, PICo, PICOC, PIO, PECO, PECODR, PECOT and PEO.
I is for Intervention. E is for Exposure.
There is a lot of content, so to make it more manageable for you, the Intervention variants are on one page and the Exposure variants are on another.