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Nature of Science

Performance Benchmark N.12.A.3
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Nature of Science
Scientific Inquiry
  N.12.A.1
  N.12.A.2
  N.12.A.3
  N.12.A.4
  N.12.A.5
 

N.12.A.6

Science, Technology, and Society
Content Areas
Nature of Science (NOS)
Life Science
Earth Science
Physical Science

Students know repeated experimentation allows for statistical analysis and unbiased conclusions. E/S

The National Science Education Standards (NSES p. 23) defines scientific inquiry as "the diverse ways in which scientists study the natural world and propose explanations based on the evidence derived from their work. Scientific inquiry also refers to the activities through which students develop knowledge and understanding of scientific ideas, as well as an understanding of how scientists study the natural world." The Science as Inquiry Standard in NSES includes the abilities necessary to do scientific inquiry and understanding about scientific inquiry.

Scientific inquiry reflects how scientists come to understand the natural world, and it is at the heart of how students learn. From a very early age, children interact with their environment, ask questions, and seek ways to answer those questions. Understanding science content is significantly enhanced when ideas are anchored to inquiry experiences.

Scientific inquiry is a powerful way of understanding science content. Students learn how to ask questions and use evidence to answer them. In the process of learning the strategies of scientific inquiry, students learn to conduct an investigation and collect evidence from a variety of sources, develop an explanation from the data, communicate and defend their conclusions.

For a complete list of NSTA Position Statements visit
http://www.nsta.org/about/positions.aspx#list

Figure 1. Natural world collage.
(from http://www.chemistryland.com/ChemEdArticle/PowerPoint.html)

Science Demands Evidence
Sooner or later, the validity of scientific claims is settled by referring to observations of phenomena. Hence, scientists concentrate on getting accurate data. Such evidence is obtained by observations and measurements taken in situations that range from natural settings (such as a forest) to completely contrived ones (such as the laboratory). To make their observations, scientists use their own senses, instruments (such as microscopes) that enhance those senses, and instruments that tap characteristics quite different from what humans can sense (such as magnetic fields). Scientists observe passively (earthquakes, bird migrations), make collections (rocks, shells), and actively probe the world (as by boring into the Earth's crust or administering experimental medicines).

From Science for All Americans Online at
http://www.project2061.org/publications/sfaa/online/chap1.htm

Science places great emphasis on evidence and data, therefore great value is placed on the development of better instruments and techniques of observation. Additionally, the findings of any one investigator or group are usually checked by others. Accuracy and precision are two terms related to the significance of scientific measurements and calculations.

Accuracy is the correctness of a measured or calculated quantity to its actual (true) value. In scientific investigations, oftentimes the accuracy of the experiment is presented as a percent error through the following equation:

Precision is the degree to which repeated measurements of the same quantity yield the same or similar results (often referred to as reproducibility or repeatability of the measurement).

Oftentimes a dartboard and darts are used to model the difference between these two terms.  Aiming at the target, your goal is to hit the bull’s eye (target center) with all five darts. The resulting patterns provide insight into the meanings of accuracy and precision.

Figure 2a-d. Dart images.
(from http://honolulu.hawaii.edu/distance/sci122/SciLab/L5/accprec.html)
Figure 2a. Neither Precise Nor Accurate. This is a random pattern, neither precise nor accurate. The darts are not clustered together and are not near the bull’s eye.
Figure 2b. Precise, Not Accurate. This is a precise pattern, but not accurate. The darts are clustered together but did not hit the intended mark.
Figure 2c. Accurate, Not Precise. This is an accurate pattern, but not precise. The darts are not clustered but their average position is the center of the bull’s eye.
Figure 2d. Accurate and Precise. This pattern is both precise and accurate.  The darts are tightly clustered and their average position is the center of the intended mark.

 

Adapting the dartboard model to scientific experimentation, poor accuracy among measurements and calculations arise from procedural or equipment flaws while poor precision results from poor technique. Individual measurements can be precise without having accuracy. This oftentimes occurs with an incorrectly used or incorrectly calibrated piece of scientific equipment such as a balance that was not zeroed prior to massing an object. Repeated measurements of the sample will yield very similar (if not identical) masses for that sample but will not reflect the true mass of the sample. However, it is not possible to reliably achieve accuracy in individual measurements without precision. As in the dartboard model, if the darts are not grouped close to one another, they cannot all be close to the bull’s eye. (Their average position might be an accurate estimation of the bull’s eye, but the individual arrows are inaccurate.  As in Figure 2c.)

Let’s explore an example using collected data.
A traditional lab experience in an introductory physics class is to determine the acceleration due to earth’s gravity (gEarth). This investigation used technology and graphical analysis software (Vernier’s LoggerPro software) to measure the acceleration of a freely falling body (g) using a Picket Fence and a Photogate.

Trail #1
         

The slope of a velocity verse time graph yields average acceleration. The analysis box in the graph above displays a slope value of 10.31 m/s2. The accepted value for acceleration due to Earth’s gravity (gEarth) is 9.81 m/s2.  Substituting the values into the percent error equation for this one trial yields an error of 5.1%.

The same experiment is repeated two more times, indicated in the data table as “Run 2” and “Latest”.

 

The acceleration (slope of the best fit line) of Run #1 is 10.31 m/s2, Run #2 is 9.83 m/s2, and Latest (Run 3) is 9.78 m/s2.  The arithmetic mean is calculated to determine the experimental average acceleration of Earth’s gravity (gEarth). Using the equation below, the experimental average acceleration due to Earth’s gravity is 9.97 m/s2.

Where,
   
x is the arithmetic mean of all the trials (or samples)
x is the experimental value from a single trial (or single sample)
n is the number of trials (or samples)

 

Using the average experimental acceleration due to Earth’s gravity from our three trials yields an error of 1.6%.

Increasing the number of trails in our experiment has reduced the error and shown that the experiment is repeatable and close to the accepted value; in other words accurate.

The average acceleration determined represents a single best value, derived from all the measurements. The minimum and maximum values give an indication of how much the measurements can vary from trial to trial; that is, they indicate the precision of the measurement. One way of stating the precision is to take half of the difference between the minimum and maximum values and use the result as the uncertainty of the measurement.

For our example, the minimum, average, and maximum values are 9.78 m/s2, 9.97 m/s2, and 10.31 m/s2. The result is g = 10.0 ± 0.25 m/s2. The precision of this experiment is 2.5%.

Scientists Try to Identify and Avoid Bias
When faced with a claim that something is true, scientists respond by asking what evidence supports it. But scientific evidence can be biased in how the data is interpreted, in the recording or reporting of the data, or even in the choice of what data to consider in the first place. Scientists' nationality, sex, ethnic origin, age, political convictions, and so on may incline them to look for or emphasize one or another kind of evidence or interpretation. For example, for many years the study of primates—by male scientists—focused on the competitive social behavior of males. Not until female scientists entered the field was the importance of female primates' community-building behavior recognized. Economic factors can also introduce bias into research. Limited resources may prohibit the scientist from access to the most advanced techniques and equipment thereby limiting the accuracy and precision of his analysis and conclusion.

Bias attributable to the investigator, the sample, the method, or the instrument may not be completely avoidable in every instance, but scientists want to know the possible sources of bias and how bias is likely to influence evidence. Scientists want, and are expected, to be as alert to possible bias in their own work as in that of other scientists, although such objectivity is not always achieved. One safeguard against undetected bias in an area of study is to have many different investigators or groups of investigators working in it.

Taken from Science for All Americans Online, found at
http://www.project2061.org/publications/sfaa/online/chap1.htm

 

Same Data Sets Can Result in Alternate (and often very different) Conclusions
Global warming and global climate change are hot topics today. Earth’s climate has changed through time as discovered through the study of ice cores, tree rings, glacier lengths, ocean sediments, and studying changes in the Earth’s orbit around the sun. Climate scientists are analyzing this data in an attempt to determine the causes of global climate change. The fact that Earth’s climate has changed in the past is not in question, however, the reasons for that change (especially since the American Industrial Revolution) is. Some scientists attribute rising levels of CO2 to human causes while others conclude these changes result from Earth’s natural cycles. Different interpretations of the data sets illustrate scientists’ disagreement in what the data means.

For more information on past climate change visit
http://www.epa.gov/climatechange/science/pastcc.html

For a detailed discussion of Earth’s atmosphere and the Green House Effect see
TIPS E12A3 Benchmark

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Performance Benchmark N.12.A.3

Students know repeated experimentation allows for statistical analysis and unbiased conclusions. E/S

Common misconceptions associate with this benchmark

 1. Students incorrectly think that evidence accumulated carefully will result in sure knowledge and that scientists are particularly objective.

Facts need to be taken in without bias to reach a conclusion.  However, it is both impossible to make all observations pertaining to a given situation and unattainable to secure all relevant facts for all time, past, present, and future.  With advancements in technology, the precision and amount of data available to scientists is greater today than ever before.  Scientists, like all observers, hold a multitude of preconceptions and biases about the way the world operates.  Therefore, it is impossible to collect and interpret facts without any bias.  Students should be aware that individuals’ experiences play a role in the interpretation of data and that alternate interpretations may be valid.  Scientists can legitimately hold different explanations for the same set of observations.

Myth 4 and 8 from McComas, William, "Ten myths of science: Reexamining what we think we know....," Vol. 96, School Science & Mathematics, 01-01-1996, pp 10.  To access this paper, visit http://www.bluffton.edu/~bergerd/NSC_111/TenMyths.html.

 2. Students may not realize that changed theories sometimes suggest new observations or reinterpretation of previous observations.

Although most students believe that scientific knowledge changes, they typically think changes occur mainly in facts and mostly through the invention of improved technology for observation and measurement.  One of the strengths of science is that experiments are the sole route to scientific knowledge and that scientific conclusions are continually reviewed.

From Benchmarks for Science Literacy On-Line by the American Association for the Advancement of Science (AAAS) found at
http://www.project2061.org/publications/bsl/online/ch15/findings.htm#Ch1

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Performance Benchmark N.12.A.3

Performance Benchmark N.12.A.3

Students know repeated experimentation allows for statistical analysis and unbiased conclusions. E/S

Sample Test Questions

1st Item Specification: Explain that repeated trials and increased sample size increase the validity of experimental results.

Depth of Knowledge Level 1

  1. A student measures the length of a pendulum three times. The measurements were 1.42 meters, 1.43 meters, and 1.45 meters.  The actual length of the pendulum was 1.89 meters. What can be said about these measurements? The measurements are
    1. accurate.
    2. precise.
    3. aligned.
    4. exact.

  1. Which term represents the degree to which data matches the true or accepted value?
    1. Accuracy
    2. Precision
    3. Correlation coefficient
    4. Alignment standard

Depth of Knowledge Level 2

  1. Use the data tables and provided information to answer the following question. Working in groups, students were instructed to develop and conduct an investigation to determine the density of silver. Each lab group was provided with an identical sample of silver. The data tables for two groups are shown below.

Group 1

 

Trail 1

Trial 2

Trail 3

Average

Mass (g)

89.3

91.5

90.2

90.3

Volume (cm3)

12.3

11.9

12.1

12.1

Density (g/cm3)

7.3

7.7

7.5

7.5


Group 2

 

Trail 1

Mass (g)

91.5

Volume (cm3)

12.8

Density (g/cm3)

7.1

Which group’s data is most likely closest to the accepted value for the density of silver?

    1. Group 1, because they conducted the experiment three times with measurements that are close to each other.
    2. Group 2, because with careful measurements only one run of the experiment is needed to ensure accuracy.
    3. Group 1, because the averaged data helps to confirm errors throughout each trial.
    4. Group 2, because they were able to complete the measurements more efficiently.

  1. Use the data tables and provided information to answer the following question. For a final lab grade, a Physics class is asked to find the rate of acceleration due to gravitational force. The class divided into five groups and began to discuss their experimental design. All of the groups decided to perform different experiments and began to collect data. The data tables of the five different experiments are shown below.

Class Data

 

Group 1

Group 2

Group 3

Group 4

Group 5

 

Velocity (m/s)

12.4

11.2

25.5

5.35

5.86

 

Time (s)

1.22

1.21

2.56

0.703

0.480

 

Calculated Acceleration (m/s2)

10.2

9.26

9.96

7.61

12.2

 

What should the class decide to do next to insure the lowest amount of error in their data?

  1. The class decides that the data is too varied so they should ignore it and run the experiments over again.
  2. Group 4 is asked to do the lab over because they have collected data that doesn’t match the other groups.
  3. The groups decide to compare their results with the other Physics classes’ results before committing to a final answer.
  4. The groups decides to vote on the best experiment and have that group run the lab again to use the new results as the correct answer.

2nd Item Specification: Explain the importance of independent replication of experimental results.

Depth of Knowledge Level 1

  1. What makes a scientific explanation different from a non-scientific explanation? Scientific explanations are
    1. based on assumptions.
    2. predictable.
    3. not able to be changed.
    4. testable.

  1. Scientists publish the details of important experiments. Which of the following is NOT a reason for this?
    1. Their work can be repeated.
    2. Their experimental procedures can be reviewed.
    3. Others can try to reproduce the results.
    4. Others can turn their experiments into technology.

Depth of Knowledge Level 2

  1. A student just received their license to drive and is in the market for a used car. After saving her money she decides to go to the dealership to look for a suitable car. The salesman points out a car that she likes, but the car doesn’t sound normal after starting. What would be the best approach the student could use to evaluate the car?
    1. The student should trust the salesman because the car has been tested at the dealership.
    2. The student should take the car to an independent mechanic because the mechanic does not have an interest in the purchase of the car.
    3. The student should ask the salesman to take the car to their mechanic to evaluate the odd sound.
    4. The student should not worry about the noise because all cars sound different.   

  1. Use the data tables and provided information to answer the following question. Working in groups, students were instructed to develop and conduct an investigation to determine the density of silver. Each lab group was provided with an identical sample of silver. The data tables for two groups are shown below.

Group 1

 

Trail 1

Trial 2

Trail 3

Average

Mass (g)

79.5

81.5

80.2

80.4

Volume (cm3)

12.4

11.8

12.1

12.1

Density (g/cm3)

6.4

6.9

6.6

6.6


Group 2

 

Trail 1

Trial 2

Trail 3

Average

Mass (g)

89.3

91.5

90.2

90.3

Volume (cm3)

12.3

11.9

12.1

12.1

Density (g/cm3)

7.3

7.7

7.5

7.5

The accepted value for the density of silver is 7.3 g/cm3

Which of the following statements below BEST explains the importance of independent replication of experimental results.
    1. Group 1 has data that is independent of Group 2, and that is why their data is more accurate.
    2. If Group 2 was not independent of Group 1, then Group 1 would not have found that they had calculated the incorrect density for silver.
    3. Because Group 1 and Group 2 were independent they could compare their results for discrepancies. 
    4. Because the groups were independent they were sure that their calculated densities were correct.

  1. A new drug, said to cure Attention Deficit Disorder, was presented to the United States Food and Drug Administration (FDA) for approval. The makers of this drug conducted a study on 20 people, in the South American rainforest, and found that 18 out of 20 patients improved their concentration while taking this medication. Based on this information, should the FDA approve this new drug?
    1. Yes, because the drug proved to be effective for most of the people that took it.
    2. No, because the drug is meant for people in cities so it needs to be tested by the drug company, on people in cities.
    3. Yes, because the drug will help people with Attention Deficit Disorder.
    4. No, because the drug company that makes the drug should hire an independent company to test the drugs effectiveness.

3rd Item Specification: Given two or more sets of data among which there is some disagreement, discuss conclusions that can or cannot be supported based on the combined data.

Depth of Knowledge Level 1

  1. In August 2006, the International Astronomical Union removed Pluto’s status as a planet and named it a dwarf planet. What prompted the reclassification of Pluto?
    1. A new telescope introduced in 2006 allowed scientists to see a better view of Pluto.
    2. Scientists based their decision on known data from Pluto and other objects in the solar system.
    3. A manned mission to Pluto provided evidence to make it a dwarf planet.
    4. Scientists were biased to make the solar system have ten planets.  
       
  1. Scientists have observed data that shows the average temperature of the Earth has risen over the past century. However, there is a debate among some scientists if the temperature rise is caused by human activity or natural climate change. What is the source of the global warming debate?
    1. Errors in the data collection process.
    2. Political bias among scientists and their position.
    3. Different interpretations of the same data.
    4. Failure of some scientists to publish their data.

Depth of Knowledge Level 2

  1. During the early 20th century stomach ulcers were common in people with high stress jobs, such as Physicians. Due to the high stress of these professions and the high rate of stomach ulcers of people in the profession, it was thought that stomach ulcers were caused by high stress. In 1982 data showed that ulcers were caused by a bacterium. The data was not widely supported as it refutes the common idea that ulcers are caused by stress. Which of the following statements are NOT supported by both lines of data?
    1. When the human body is under high stress the immune systems function slows.
    2. Pilots are at a high risk for ulcers because of their stress level and contact with many different diseases due to travel.
    3. Watchmakers are at a low risk for ulcers because they typically work in a low stress environment and have little contact with others.
    4. All people have stress, but not all people have ulcers.


  2. Pellagra is a disease that first appeared in the United States in the 1820s and was known as the disease of the four Ds: dermatitis, diarrhea, dementia, and death. There was a debate among scientists if pellagra was caused by poor diet or an infectious agent. Which of the following supports the fact that pellagra is caused by a poor diet?
    1. Pellagra was common in the North, especially in universities and business offices.
    2. Orphans provided with fresh vegetables, meat, and milk recovered from Pellagra or never got it.
    3. Staff at institutions such as hospitals, prisons, and orphanages did not develop Pellagra.
    4. Pellagra was not common in sailors, especially sailors that crossed the Atlantic Ocean.

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Performance Benchmark N.12.A.3

Students know repeated experimentation allows for statistical analysis and unbiased conclusions. E/S

Answers to Sample Test Questions

  1. B, DOK Level 1
  2. A, DOK Level 1
  3. A, DOK Level 2
  4. C, DOK Level 2
  5. D, DOK Level 1
  6. D, DOK Level 1
  7. B, DOK Level 2
  8. C, DOK Level 2
  9. D, DOK Level 2
  10. B, DOK Level 1
  11. C, DOK Level 1
  12. D, DOK Level 2
  13. B, DOK Level 2

 

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Performance Benchmark N.12.A.3

Students know repeated experimentation allows for statistical analysis and unbiased conclusions. E/S

Intervention Strategies and Resources

The following list of intervention strategies and resources will facilitate student understanding of this benchmark.

1. Accuracy vs. Precision, and Error vs. Uncertainity

A comprehensive review of measurement and error from Bellevue Community College.  Scroll down through the text to participate in a practice quiz reviewing these concepts.

To access the tutorial and practice quiz, go to
http://scidiv.bcc.ctc.edu/Physics/Measure&sigfigs/B-Acc-Prec-Unc.html

 

2. Visualizing Scientific Data: An Essential Component of Research by Visionlearning

This site contains a wealth of information related to both science process and content standards.  Emphasized here is importance of collecting and analyzing data as a fundamental component of any scientific endeavor. 

A simple three step procedure helps with reading any kind of graph. 

  1. Describe the graph: What does the title say? What is on the x-axis? What is on the y-axis? What are the units?  
  2. Describe the data: What is the numerical range of the data? What kinds of patterns can you see in the data? 
  3. Interpret the data: How do the patterns you see in the graph relate to other things you know?

To access the information on data presentation, go to
http://www.visionlearning.com/library/module_viewer.php?mid=109&l=&c3=

 

3. Scientific Writing: Peer Review and Scientific Journals by Visionlearning

This article outlines the process of peer review, in which scientists evaluate the value and credibility of research before allowing it to appear in print.  Reviewers consider only the quality of the science before from the materials and methods used in the experiment to the data collected and the author’s interpretation.

To access this article visit
http://www.visionlearning.com/library/module_viewer.php?mid=123&l=&c3=

 

4. Measurements and Calculations from Science Help Online for Chemistry

This site has been designed to aid students who are learning Chemistry, by providing them with additional lessons, worksheets, and review materials.  Each of the lessons on this site were written by Greg Curran, a Chemistry teacher and the author of Homework Helpers: Chemistry.  Most of the support materials were produced by the students of Fordham Preparatory School. Specific to assisting with this benchmark is Chapter 2: Measurements and Calculations, and further exploration of the various chapters will provide resources across the science disciplines.

To access the Accuracy and Precision background and supporting resources follow
http://www.fordhamprep.com/gcurran/sho/sho/lessons/lesson22.htm

To explore the chapters of this online book and its available resources, go to
http://www.fordhamprep.com/gcurran/sho/sho/review/revindex2.htm


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