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Variables There are 4 FOUR!
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What? VARIABLES AND CONTROLS: There are four! (The first two are the IF & THEN of your Hypothesis.) Type in outline form, not sentence form: 1. VARIABLE TO BE CHANGED (aka: the independent variable) (This is the IF...If I do this): Example: The amount of aspirin you give to plants: 0 mg, 2 mg, 5 mg, 10 mg, 20 mg, 40 mg, 80 mg, or 100 mg. Be as specific as possible-- First, list everything that can change including amounts, intervals, conditions-- everything! Now choose the one to answer your question. We need to get it down to ONLY one in the end by controlling the rest. Example: In our experiment with plants the ONE VARIABLE you would CHANGE would be different amounts of aspirin your different plants are given in water. All the plants would receive the same amount of water and light (controls). However, you would list the actual aspirin concentrations to be given to the different plants (change). 2. VARIABLE TO BE MEASURED (This is the THEN...Then the effect you are expecting & need to measure) (aka: the dependent variable... the results that depend on what you change): This dependent VARIABLE is the results from that change you are trying. You need TO MEASURE the effect (called quantifying). It is NOT everything else that you measure (those go under controls!) Example: The resulting average growth that you measure following the aspirin administration and 3 weeks of growth time. 3. CONTROLS (things you are trying to keep the same so you will be measuring them!!!): These are factors that must remain the same in ALL GROUPS during the experiment. These factors are known as VARIABLES TO BE CONTROLLED, or simply, "CONTROLS". This IS the stuff you measure to make sure you are controlling them! Example: a) Type of plants is all the same, 5 plants for each category. b) Age of plants: all started at the same time. c) Same water and measured amount administered at the same time of day d) Room temperature, amount of light, and soil measured the same for all plants 4. CONTROL GROUP (a group where you did NOT make the change but did everything else) (the "normal group" used for COMPARISON with the experimental changed group): A CONTROL GROUP is a separate experimental group that is in a "normal" condition in which you do NOT apply the VARIABLE YOU ARE CHANGING IN THE OTHER EXPERIMENTAL GROUPS. The CONTROL group is used for a standard, FOR COMPARISION with the experimental subjects. Our plant experiment would have to contain 1 group of plants given NO ASPIRIN. Example: The control group would be: The group that never receives aspirin. REMEMBER most experiments need: 1. a CONTROL GROUP (that you compare to), 2. ONE CHANGED (independent) VARIABLE, 3. ONE MEASURABLE (dependent) VARIABLE, and 4. ENVIRONMENTAL CONTROLS (that you measured!). **** Don't get "CONTROLS" mixed up with the term "CONTROL GROUP". In our plant experiment, we would make sure ALL PLANT GROUPS were given the same type and amounts of water at the same time of day; they would be exposed to the same controlled temperatures, provided identical environments, lighting would remain the same, etc. Those are the controls. The Control Group would simply not receive any aspirin. Record Variables and Controls in your Science Project Log. You will also need a TYPED copy for your notebook and me. |
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