Statistics for Action Activities
Facilitator Instructions
Averages: Imagine the Extremes
Activity Overview
Since some EPA regulations are based on an average, a claim like, “Our
emissions are under the limit,” could cover up a potentially hazardous
scenario. Participants imagine numbers and make a graph with low, high,
and middle values that could be represented by the average given. Graphing
the possibilities empowers community members to show an actual or
potentially harmful situation.
When to Use It
When reported results include averages that seem to conflict with suspected
problems.
Suggested companion activities
Skill: Make a case that a harmful or not harmful
situation exists; Unpack an average to show what
extremes an average could hide.
Time: 10-20 minutes
Data set: Provided, or substitute your own
Versions available: Opacity; Soil Composites;
Trihalomethanes in the Drinking Water
Materials & Prep
Copy the participant instructions (1 per pair or
participant).
Calculators
• Follow up with Design a Poster
Graph paper
Steps
1. Launch the activity: People in this community have witnessed problems
with the [air/soil/water], but the data don’t show it. Let’s look at what the
data could be hiding.
2. In pairs or as a group: Follow the directions to create a data set.
3. Debrief:
• What possible readings did you come up with?
• How else could we use data like this?
• What readings are a concern that we should highlight in flyers (or other
outreach materials/conversations/hearings)?
Worth Noting
Averages are more appropriate in some situations than in others. One loud
blast could damage your hearing, but averaged over a year the sound would
seem acceptable.
Below are sample data sets for the Soil Composite version.
Test Pit 1
lead result in mg/kg (ppm)
0-2 feet
450
2-4 feet
350
4-6 feet 25
Test Pit 2
Sample Opacity Readings
lead result in mg/kg (ppm)
0-2 feet
375
2-4 feet 275
4-6 feet 175
Time in Minutes
Smart Moves
• Compare it.
• Play with different ways to show and say it.
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Averages: Imagine the Extremes
Opacity
Background
The North Carolina Division of Air Quality regulations require that visible
emissions for hot mix asphalt plants have an opacity* of less than 20%
when averaged over a six-minute period.
Neighbor
Facility Employee
Imagine a scenario where the readings taken by the facility employee agree
with what the neighbor saw.
Directions
1. Describe in words what could be going on.
2. Create a graph to show six opacity observations made at 1-minute
intervals that fit the scenario. (Use the grid provided.)
3. Discuss with your partner: What readings are a concern that you would
highlight in a flyer or in a letter to the editor?
Note: *Opacity means the capacity to block light. Informally we say “thick” smoke. EPA Method 9 - Visual
Determination of the Opacity of Emissions from Stationary Sources requires that more opacity observations be
recorded than in this example: at 15-second intervals for a total of 24 observations over 6 minutes. Violations of
opacity standards indicate hazardous particulate matter.
Averages: Imagine the Extremes
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Opacity
(%)
100
80
60
40
20
0
0
1
2
3
4
5
6
Time (minutes)
Averages: Imagine the Extremes
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Averages: Imagine the Extremes
Trihalomethanes in the drinking water
Background
EPA regulations require that the average of any four samples of drinking
water have no more than 80 ppb of trihalomethanes.
Iʼm sorry to report that the townʼs November
sample was high in trihalomethanes. Our average
the last two months is above the limit set by the
EPA.
City Worker
Directions
1. Imagine and describe the levels for the year.
2. Create a graph to show four possible trihalomethane levels taken during
the year with an average over 80 ppb.
3. Discuss with your partner: What readings would you mention to
explain your concern to a decision maker, in a letter to the editor, or to a
neighbor?
Note: Trihalomethanes are a toxic carcinogen created when chlorine reacts with water. Decreasing trihalomethanes
in drinking water is easy. Leave the water in an open pitcher for 3-4 hours. (Source: Columbia Missiourian, July 15,
2008 and www.theolivebranch.com/water/trihalo.htm)
Averages: Imagine the Extremes
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Averages: Imagine the Extremes
Soil Composites
Background
Soil samples are often mixed together into a composite from various
depths. The lab tests the composite sample and reports one level for each
contaminant.
Of course we want to start building
houses on this former industrial
property. All the soil test results came
back below the regulatory limits
established by the state DEP. Look at
the data in the report yourself!
Whatʼs the problem?
Community Member:
These samples are composites.
They are an average and that
doesnʼt tell us enough. Is there
any risk for future residents of
the property?
Two test pits were completed with composite soil samples at various depth and analyzed for lead.
The average is 267 mg/kg, which is below the residential standard in this state (300 ppm).
Directions
1. Create a graph to show the levels taken at 0-2 ft, 2-4 feet, and 4-6 feet.
(You can use graph paper or a calculator.)
2. Discuss: Use your graph and practice explaining your concern to a
decision maker, to a neighbor, or in a letter to the editor.
3. What additional information would be important when looking at this
data? Think about source and exposure.
Averages: Imagine the Extremes
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