we introduced pandas and the way to work with pandas and dataframe objects pandas very powerful tool we'll use it more in future sectionsbut make sure you're starting to take notice of these things because these are going to be important techniques in your python skills for managing large amounts of data and organizing your data multi-level models it makes sense now to talk about multi-level models this is definitely an advanced topicand ' not going to get into whole lot of detail here my objective right now is to introduce the concept of multi-level models to youand let you understand some of the challenges and how to think about them when you're putting them together that' it the concept of multi-level models is that some effects happen at various levels in the hierarchy for exampleyour health your health might depend on how healthy your individual cells areand those cells might be function of how healthy the organs that they're inside areand the health of your organs might depend on the health of you as whole your health might depend in part on your family' health and the environment your family gives you and your family' health in turn might depend on some factors of the city that you live inhow much crime is therehow much stress is therehow much pollution is there and even beyond thatit might depend on factors in the entire world that we live in maybe just the state of medical technology in the world is factorrightanother exampleyour wealth how much money do you makewellthat' factor of your individual hard workbut it' also factor of the work that your parents didhow much money were they able to invest into your education and the environment that you grew up inand in turnhow about your grandparentswhat sort of environment were they able to create and what sort of education were they able to offer for your parentswhich in turn influenced the resources they have available for your own education and upbringing these are all examples of multi-level models where there is hierarchy of effects that influence each other at larger and larger scales now the challenge of multi-level models is to try to figure out"wellhow do model these interdependencieshow do model all these different effects and how they affect each other?