GED Science Practice Test: Experimental Controls

In many experiments, scientists will want to include an experimental control, sometimes called a control group. An experimental control is an additional test in which the scientist does not manipulate anything.  Experimental controls help scientists be certain that the observed effects in the dependent variable are actually caused by the independent variable.  It provides a point of comparison to check the effects of changing the independent variable.

If this is difficult to understand, it might help to consider the idea of an experimental control in reference to the radish experiment. In this experiment, the experimental control would be a test in which a radish plant was given no magnesium.  This is important, because without it, you might make incorrect conclusions about the collected data.  Consider again the following table:

Table A:  Quantitative Data/No Experimental Control


From this table, you might conclude that magnesium helps the plants grow tallest at a concentration of .25 grams/liter.  Consider however, the same table with an experimental control with no magnesium added to the radish plants:

Table B:  Quantitative Data/Experimental Control

This table would lead you to conclude that the magnesium actually HARMED the growth of the plants at all concentrations.  (Note:  Magnesium does actually help plants to grow, so this data for the experimental control is hypothetical and does not reflect reality.)


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