Types of Graphs

Visualizing data in graphs allows scientists to detect patterns and observe the variability of the sampled data.  

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• Click to learn how to graph in Sheets. 
• Click to learn about interpreting error bars on graphs.
• Click to read a short article about the effective use of graphs.

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Pie Chart

A pie chart  is used when there are no "levels" of a manipulated (independent) variable and the responding (dependent) variable is qualitative.  Pie charts show proportions for groups of data in relative to the whole data set. The entire pie represents all the data, while each slice or segment represents a different class or group within the whole. The number of categories should be generally limited to between 2 and 10.

Bar Graph

A bar graph depicts a qualitative manipulated (independent) variable and quantitative responding (dependent) variable.  Use a bar graph if the data sets are not skewed (meaning they fit a normal distribution) and you have calculated the mean as a measure of central tendency and the standard deviation as a measure of spread.  The bar represents the mean and the error bars are the standard deviation of each data set.  If you had less than 5 trials for each level of your manipulated variable, then use the RANGE for the “error” bar instead of the standard deviation.

Box and Whisker

A box-and-whisker plot  depicts the median as a measure of central tendency and the interquartile range as a measure of spread.  Box-and-whisker plots may also identify the outlier data. The spacing between the different parts of the box indicates the degree of dispersion and whether the data distribution is symmetrical or skewed.

Ex:  Comparison of the mean reaction rate for five different enzymes

Histogram

Histograms depicts the frequency of groups (bins) of continuous quantitative  data.  In histograms, there are not gaps between the the bars. Individual data points are grouped together in classes to show the frequency of data in each class. These graphs can be used to check if a data set follows a normal distribution.

Scatter Plot

A scatterplot is used to show the relationship between two variables and whether their values change in a consistent way. Scatterplots are used with qualitative variables to see if they are correlated.  Lines and curves of best fit are used to represent the trend of data points on a scatterplot.

Scatter Plot
with Means

Scatterplots can be use to depict the mean as a measure of central tendency and the standard deviation as a measure of spread.  

Stacked Bar

A stacked-bar chart is used to show how a total amount is divided into different parts (part-to-whole relationships) across multiple categories of a manipulate (independent) variable.