Data Analysis Now that you have collected a significant amount of data it is time to complete the data analysis portion of Step 5: Data Collection & Analysis. In the next section, you will determine what your data mean and draw a conclusion. Below are some sample raw data sets, analysis, and graphs. Your mentor and/or chapter coordinator will help you determine which type of graph is best for your data. If you are inexperienced in Excel or another computer graphing program, ask your mentor for assistance in creating your graphs. Calculating Your Data The mean of your data is the average. To calculate the mean of a set of data, add all the values and divide by the number of data entries. The mode is the value that occurs most frequently in your data set. To compute the mode, count the number of times each value occurs in the data set and then choose the data value with the highest sum. The median is the central value of an ordered distribution. To obtain the median, order the values from the lowest to the highest and select the data value that occurs in the middle of your distribution. If your data set has an even number of entries, the median is the mean of the middle two values. (Almost everyone will need to calculate mean values for their data sets. Calculating the mode and median values may not be useful. If you’re not sure, consult your mentor.) Graphing Your Data: Basic Graph Types Bar Graphs are used to show relationships between groups. The values being compared do not need to affect each other. This type of graph is an easy way to show large differences. Line Graphs are used to show how changes in one variable affect changes in another variable. Most line graphs are created by plotting the independent variable on the x-axis (bottom) and the dependent variable on the y-axis (left). Line graphs can also be used to show how data change over time. Pie Graphs are used to show how part of something relates to the whole. Pie graphs are used to effectively show percentages.
Example 1: Using a bar chart to show the differences in rates of water percolation through different types of soil.
A student set up her experiment by placing a clean piece of filter paper in four different funnels. To three of the funnels, she added 25 mL of sand, clay, and soil, respectively. The fourth funnel had just the filter paper, and served as the control data set. She then poured 25 mL of water through each funnel, and measured the time, in seconds, it took for all the water to percolate through the funnels. She repeated her experiment a total of three times. Her raw data sets, her mean values, and her bar chart are shown below. Notice that she used her mean values to create her bar chart.
Trial 1
Soil type
Trial 2
Trial 3
Mean
Time (seconds)
Sand
40
41
45
42
Clay
55
60
57
57.3
Potting Soil
21
23
27
23.7
Control
8
5
4
5.7
Comparing Water Percolation Through Different Soil Types 70
Percolation Time (sec.)
60 50 40 30 20 10 0 Sand
Clay
Soil Soil Type
Control
Example 2: Using a line chart to show the changes in river flowrate over time. A student measured the flowrate of water in four of his local rivers. Note that in this experiment, there is no control group, the student is comparing the different experimental data sets to each other. The student measured the flowrate three times during the transition from winter to spring with the assistance of his mentor and a park ranger. His raw data sets and his line chart are shown below.
January 1
River
February 1
March 1
Flowrate (cubic feet per second)
Klamath River
375,000
327,000
320,000
Eel River
647,000
542,000
498,000
Trinity River
166,000
161,000
131,000
Mad River
62,000
57,000
38,000
Comparing River Flowrates 7.0E+05
Flowrate (cu. ft/sec)
6.0E+05 5.0E+05 4.0E+05 3.0E+05 2.0E+05 1.0E+05 0.0E+00
1-Jan
1-Feb Klamath
Eel
1-Mar Trinity
Mad
Example 3: Using a pie chart to show the different bird species observed on the Outer Banks of North Carolina.
A student counted the number of different types of birds she observed during a two-hour period at a specific beach location. She returned to the same location three days in a row and counted birds during the same two-hour time block. Her raw data sets, her mean values, and her pie chart are shown below. Notice that she used her mean values to create her pie chart.
Day 1
Type of Bird
Day 2
Day 3
Mean
Number of birds
Pelican
10
12
15
12.3/66.8= 18%
Sanderling
20
18
17
18.3/66.8= 27%
Great Egret
15
16
15
15.3/66.8= 23%
Snowy Egret
9
8
11
9.3/66.8= 14%
Other
12
10
13
11.6/66.8= 17%
Birds Observed at Emerald Beach 17%
18%
14%
27%
23%
Pelican Sanderling Great Egret Snowy Egret Other