Welcome to science buddies and thank you for the question.
It is very important to pick your variables correctly. Independent variables are those that you as the scientist changes. A good experiment should have only one independent variable. The dependent variable are those parameters that change and are observable in response to the change in independent variable. There can be more than one dependent variable. In your case, the independent variable is ball cost. Your dependent variable is distance. The reason I suggest your independent be cost instead of ball type is that you could get 2 different ball types for the same price,and get different performance out of each, but not prove/disprove that cost=performance. In fact, to really prove this, i would get 3 differently priced golf balls but ensure they were from the same manufacturer (i.e. all made by ping). I might even take it a step further and get three ball types from the three top manufacturers to see if the performance difference between each price point is consistent across manufacturing. Also, i would ensure i got all balls from the same store location to ensure unit price markup was the same, or else find the manufacturers suggested retail price for each.
In this case you don't have a control group, per se. You are doing a comparison analysis across all ball types. Your control is measuring distance from a single location, such as from the tee.
For more info on variables, visit the project guide on this site located at the following link:http://www.sciencebuddies.org/science-f ... ndex.shtml
Hope this helps.
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