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The most fundamental critical thinking tool used in science to advance our understanding of the world is stating a hypothesized explanation of an observation and testing that hypothesis with evidence. For example, you return from a trip and find one of your house plants looking dead. Examining what is already known about plants, you suspect that failure to water the plant while you were gone caused it to wilt. Your hypothesis would be that water causes plants to grow.

The next year you go on a trip and ask a friend to water your plants when you are away. When you return, the plant that replaced the one that died the previous year is dead. There is obviously some important factor that you did not take into consideration. What are the other possible factors that you could have overlooked? Such factors that make it difficult to interpret your results correctly are "confounding factors" (CFs) and must be considered in addition to the factor you hypothesized as responsible for what you observed.

Item Included:	Example:	Explanation:
Statement: your explanation	Plants will grow only if they receive water, or they wilt and die.	This statement hypothesizes an effect of water and the response of plants to the lack of it.
Ideas (3) in statement: each single idea in a separate sentence	1. Plants require water to grow. 2. Plants wilt if they lack water. 3. Plants die if they lack water.	These are ideas contained or implied in the statement that you can test, one at a time.
Causal Factor: the factor you think had the effect you observed	Water	Water is the factor that you think had the effect you observed.
AH: what you want to prove	Water causes plants to grow.	Write a simple sentence (one independent clause) using one of the single ideas listed and state how the (causal) factor - water in this example - will exert an effect on something - plants in this example.
NH: direct contrast to AH	Water does not influence plant growth.	Write a sentence that states that the causal factor has no effect, has no influence, or does not make a difference, and provides a direct contrast to the alternative hypothesis.
Null Element: why NH is null	null=no effect of water	Identify the element in the null hypothesis that nullifies the effect of the factor you are testing.
Experiment or analysis: details how you will test if the causal factor has an effect	Two plants, one watered with different amounts (experimental treatments) and one not watered at all (the control). Each condition will be replicated with at least 3 individuals to account for variation in response of the individual plants to the treatments.	You need to include enough detail in your description to show that your test will provide the evidence required to test the hypothesis. Include the kind of subjects you will use and the number of subjects needed.
What are the 3 most important CFs: factors other than water that can affect plant growth	Sunlight, nutrients, herbivores/parasites	Factors other than water can also affect plant growth. Those other factors need to be considered and adjustments made for them so that they don't make it difficult or impossible to estimate the effect on plants of water alone.
E (hypothetical) what you will measure for the causal factor, its effects, and the CFs	Measure the health of the plants by color of foliage, by rigidity of the stem, and by rate of growth. Measure and record the amount of light, the availability of soil nutrients, and the soil moisture. Count herbivores and parasites. Expect greater growth with more water applied.	Not only is it necessary to measure the causal factor, its effect, and all the confounding factors, you need to say what aspects of them you will need to measure to obtain the evidence required to make a valid comparison of the results from the experimental and control conditions.
How to eliminate, control, or adjust for the effects of CFs: so you can see what the causal factor did	Each treatment will use soil from the same source under growth lights. Sterilize the soil to eliminate potential parasites. If the greenhouse contains potential herbivores (e.g., bugs), eliminate them. At the end of the experiment, examine the plants and their roots to detect any signs of parasites or herbivores.	You can eliminate effects of the confounding factors by keeping them all constant. Then the results will be limited to only those constant conditions. On the other hand, you can allow confounding factors to vary and use statistics to estimate the effects of each confounding factor and the combinations of factors so that their effects can be removed from the total combined effect, leaving you with an estimate of the effect of the causal factor by itself.
E (actual): describe an experiment reported in a publication - what was actually measured and what results observed	Plant growth was measured in a greenhouse given increments of water. Growth was greater for each increment of water applied.	This information would come from an experiment conducted by someone else and reported: what was the experimental setup, what was measured, and what were the results.
How were the effects of CFs eliminated, controlled, or adjusted for:	Potassium, phosphorus, and nitrogen were mixed in the soil for all replicates. Standard type A growth lights were used. The greenhouse was kept free of herbivores and parasites.	Describe how the researcher adjusted for the confounding factors in his/her experiment.
Citation for source of information:	Scott, J. 1934. Optimal watering regime for greenhouse plants. Journal of Horticulture. 23:14-18.	Cite the source of the information you included in your answers, according to the class citation format.
Personal Response:	I prefer to have desert plants because it's not necessary to water them much.	Write a comment that is relevant to this week's statement.

Note: Providing your answer in the three cells in red is less preferred than describing your evidence in the three cells above the red cells. Although sample answers are given in both sets of cells, you need to give your own answer in only one of the sets of three cells.