How to decide whether an effect is fixed or random in mixed models

If you need help going from wide to long format, see these videos: https://youtu.be/_86IlMSI3o4 https://youtu.be/4-sqsCANxHU https://youtu.be/dcWuHcC98EU To see other mixed model videos, see this link: https://youtube.com/playlist?list=PL8F480DgtpW9_IT7xN1XeRF_dglZmK0nM