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The Living Environment, Standard 1, Key Idea 3, Performance Indicator 3.4

Original Statement:
Based on the results of the test and through public discussion, revise the explanation and contemplate additional research.

Interpretation:
Depending on the results of your experiment, you may need to change your conclusions and do another experiment

Example:
A student hypothesized that, "If a pond is next to land on which pesticides are sprayed, then there will be an unusually large number of fish tumors ". After completing an experiment to test the hypothesis, the data showed that 50% of the fish from a pond near a field that had been sprayed with pesticides, had tumors. The student concluded that pesticides do cause an increase in tumors." However, other students pointed out that the conclusions might not be correct because there were no control ponds studied (ponds near unsprayed fields). How do we know whether or not the fish in ponds near unsprayed fields also have a 50% tumor rate ? The experiment needed to be repeated in ponds near unsprayed fields.

Case Study
From 1942 to 1953, Hooker Chemical in Buffalo N.Y. dumped 22,000 tons of mixed chemicals in a canal called Love Canal. The 55 gallon drums were then covered with dirt.
In 1955 the dump site was sold to the Niagara Falls School Board for $1.00. The school board built a school on the site and a neighborhood of several thousand people developed on and around the site. In 1975-76, heavy rains forced some of the barrels and chemicals to surface. Residents soon complained of various health problems, including miscarriages, rashes, and various illness, etc.. In 1978, because of complaints from residents, the NYS Department of Health performed a survey and blood tests to determine if the site was dangerous to the health of the residents. As a result of this study and several others, over 2500 residents were eventually relocated by the government to places outside the Love Canal area. Some people, however, continued to live at the site.
In 1980 the Environmental Protection Agency undertook a study, because of a concern over high cancer rates in the area, to determine if there was a high rate of chromosome abnormalities in the area. The study found abnormalities in 12 of 36 residents sampled and concluded that chromosome abnormalities were significantly higher in the Love Canal residents as compared to a historical control group (prior residents). The study, however,
was criticized because no similar studies were performed in the area surrounding Love Canal community. In 1981 the Center for Disease Control (CDC) conducted another chromosome study that included the area around the Love Canal site. This study found no significant difference in chromosome damage between the Love Canal residents and surrounding residents. This study, however, has also been criticized.

Questions:
A. Why was the chromosome study performed and what was the problem in the original chromosome study ?
B. How did the CDC study address the concerns over the original chromosome study ?
C. What might be some reasons why even the CDC study was criticized ?

References: ____________________________________________________________

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Copyright 2000 by Stephen J. Pitoniak. All rights reserved. See exemptions on title page.

TEACHER LESSON GUIDE

The Living Environment, Standard 1, Key Idea 3, Performance Indicator 3.4

Tips

Ask the students to discuss situations in which they made a decision and then had to change their mind. Discuss the reason for the changed decision.

Ask students to compare how police might be forced to change their minds about a murder suspect as they obtain more evidence, to what happens as scientists collect more evidence about a certain theory or problem. You might want to create a murder mystery game in which clues are gradually introduced.

Relate the student experiences, mentioned above, to revisions in scientific ideas (ex. biologist previously thought humans had 47, not 46 chromosomes, etc.).

Supply students with textbook reference pages to read articles that are related to controversial ideas that have been or are being revised (ex. certain ideas related the evolution of the first forms of life, etc.)

Answers to Questions

A. The chromosome study was performed to see if exposure to the toxic chemicals had caused chromosome damage. The problem with the study was that the original chromosome investigation did not include a control group to compare to the Love Canal residents.

B. The CDC conducted a chromosome study of people that did not live in the Love Canal community .

C. The CDC might have been criticized if they did not survey a large number of people, if they did not take into account variables such as smoking or drinking habits, if they did not investigate whether these other people might also be exposed to toxic chemicals, etc.