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Biology: Biology Basics: 05: Interpreting Graphs
MEDICAL ANIMATION TRANSCRIPT: Let's look at different types of graphs and see how they work. Graphs are diagrams that display data in an organized and easy-to-read fashion. Note that all graphs must have a title that summarizes this data. There are different kinds of graphs, so it's important to know how to interpret each type. When you know how to do that, you will be able to create a graph of your own. The types of graphs we will look at are X-Y graphs, line graphs, area graphs, bar graphs, and pie charts. First, we'll look at X-Y graphs. X-Y graphs, also known as scatter plots, look at how two events or variables are possibly related. The horizontal X-axis shows data that represents the independent variable. Remember, the independent variable is the variable you're intentionally changing or testing in an experiment. For example, the independent variable might be how long a student studies. The vertical Y-axis shows data that represents the dependent variable. You may recall that the dependent variable is the outcome you're observing or measuring as a result of exposure to the independent variable. For example, the dependent variable could be the grade that corresponds with how long a student studied. You can use X-Y graphs to look for trends in the relationship between the independent and dependent variables. If the values of both of these variables rise, then a line connecting the data points will show an upward trend. This means the variables are positively correlated. Now, let's change the graph to show how class grades are affected as the study time goes down. If the values of both variables go down, then a line connecting the data points will show a downward trend on the graph. Note that this is also described as a positive correlation. A positive correlation means the values of both variables are increasing or that the values of both variables are decreasing. So, what is a negative correlation? In a negative correlation, one variable goes up while the other goes down. Here, we're showing how class grades might go down as the number of missed classes goes up. So a line connecting the data points will show a downward trend. Remember, variables are negatively correlated when one value is increasing while the other value is decreasing. In some cases, the variables might follow a random pattern and have no relationship. As an example, this graph plots student height with class grades. As you can see, these variables demonstrate no correlation. Now, let's talk about line graphs. Line graphs are used to track certain changes as measured on the Y-axis, usually, over a period of time, as measured on the X-axis. This line graph shows the number of magazines sold over the course of a week. Reading this graph, you can see the most magazines were sold on Thursday and the least number of magazines were sold on Friday. Next up are area graphs. Area graphs are a combination of multiple line graphs. When making an area graph, each line graph usually has a different color underneath, with a color key that identifies what each line represents. Area graphs are useful for comparing datasets and identifying trends, such as what items are hot sellers or weak sellers in each month. Now, we move to bar graphs. A bar graph can compare different groups, such as the number of people who own different pets. Like line graphs, a bar graph can also track changes over time. The last type of graph we'll talk about is a pie chart. A pie chart shows the various parts that make up a whole. A pie chart often looks like a pizza cut into uneven slices. Just like all the pizza slices put together make up 100% of the pizza pie, all the sections of a pie chart represent different amounts that add up to 100% of the total amount. For example, in a classroom of 30 students, this pie chart represents how many have brown eyes versus blue eyes versus green eyes. Pie charts don't show trends, they just show how things are distributed within a group. So to review, graphs are an organized way to show data. X-Y graphs show how an independent variable on the X-axis relates to a dependent variable on the Y-axis. Line graphs also have X and Y axes but track changes that take place usually over time. Area graphs are a combination of multiple line graphs. Bar graphs compare values or track changes over time. And pie charts show the various percentages of things within a whole group.