Scatter plots and Bar Graphs

Scatter plots and Bar Graphs

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00:00
hi folks today we're going to be focusing a little bit more on graphing and starting to think about when we might want to use different graphs when we're looking at these large data sets like from project budburst so last class we took a lot of time to explore scatter plots and today we're we're going to introduce bar graphs but when might we want to use each of these and why so scatter plots are really important when we're talking about relationships and bar graphs are more useful when we're talking about comparisons so in a scatter plot you are looking at two
00:31
large sets of numbers on the x-axis you have your independent variable and on your y-axis you have your dependent variable and using a program say like Google Spreadsheets or Excel or any number of other programs you're plotting all of the values that are given and looking for a trend you can help yourself while you're looking for a trend by calculating something called the line of best fit or a trend line and then looking at the r-squared value which tells you how well this line fits the given data there are three kinds of
01:04
relationships that can fall out of a graph like this and that is a positive correlation a negative correlation or no correlation this tells you the relationship between the variables on the x-axis and the variables on the y-axis in the case of a bar graph you're not looking at relationships instead what you're looking at are comparisons so here much like our scatter graph you still have an independent variable on the x-axis and a dependent variable on
01:36
the y-axis and as with the scatter plot you're plotting numbers on the Y but here your x axis is not necessarily a large set of numbers but rather a set of categories so this could be anything but given our budburst data some of the likely categories are a species of tree or a different environment that a plant might live in like urban or rural or even trees of a particular age that could be grouped together into different category
02:07
on your y-axis you still have a large set of numbers and again we're looking at the dependent variable so things like age through diameter at breast height or budburst timing here's a trick why do we see just one number plotted when there are lots and lots of numbers I said it was a large data set where did the rest of the numbers go well one of the ways that scientists create bar graphs is by starting with an average and so today in our own bar graph tutorial the first
02:39
thing that we're going to learn about is how to get Google Spreadsheets to calculate the average for us so the take-home message is this there are two major types of graphs that we're going to see in these science papers one are scatter plots and the second are bar graphs these are useful for different kinds of questions a scatter plot might be useful to say whether or not a tree verse early in the north versus the south but a bar graph would be more important if we are looking at the budburst timing between multiple species
03:10
of trees okay that's all you need to know go ahead and move on to the bar graph tutorial [Music]

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