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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


/Mean,%20Median,%20Mode_0