 key ideas prerequisites and misconceptions key ideas introduced in this unit environmental data contain many variables and they are often linked a graph is a visual representation of data analysis and a useful tool in science judging whether or not differences are meaningful concepts and relationship  students will learn to create meaningful graphs learn to read different types of graphs and understand what they show analyze data to determine relationships or differences learn to interpret data vocabulary  learning the vocabulary to talk about data can be difficult here are some key terms you might begin to establish with your class as you work toward final presentations  mean  for our purposes the average add all the values and divide by the number of values statisticians will tell you there are lots of types of means but this isn t relevant to our level of inquiry median  the middle value in a set of numbers for example of 34567 5 is the median the middle value  variability  the spread of the data  meaningful differences  when comparing groups we want to know if the differences if any are large enough that they mean something in the real world for example if someone offered you 10000 and someone else offered you 10001 you really wouldn t care which you picked it s just a penny but if someone offered you 10000 and someone offered you 12000 you d probably want the 120 it s definitely more and the extra 20 makes a difference to you our data plots give us tools to help make the judgment whether a difference is meaningful or not  correlation  the degree to which two things are related for example if bigger fish have more mercury and this pattern is clear we would say that mercury concentration and fish size are correlated we talk about strong or weak correlations strong correlations mean the relationship is very tight whereas weak correlations mean that there s a lot of variability in the data things may be positively correlated as one thing gets bigger the other gets bigger too or negatively correlated as one thing gets bigger the other gets smaller see the activities below for more detail student prerequisites  the purpose of a graph and what it looks like basic math skills calculate an average etc  misconceptions about mercury  it doesn t matter which is the x axis and which is the y axis data can be put on a graph in any order graphs are only used in math class all the data given should be plotted as opposed to judging and choosing relevant data in a complex system   mercury in watersheds  