Experimental Design

Experimental Design - Experimental Design Once you have...

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Experimental Design Once you have determined the hypotheses to be tested there are several other issues that you must decide as you begin to design your  experiment. 1. The number of variables to be manipulated (1) If more than one variable is altered, there is no certainty about which variable caused the effect you were examining - at least without  using a very complicated experiment.   2. Controls You need a standard to compare your results to, something in order to know if the condition you varied had any effect. For instance, to know if additional light resulted in increase in plant growth rate, you 1 st  must know the plant's growth rate under the  same conditions without additional light. You need to control for any factors that might create an effect due to your experimental design. For instance, the lamp in a plant growth  experiment will give off both light and heat.   3. Replicates Replicates assist in determining whether variation detected is experimental error or true biological variability. The number of replicates  depends on how reliable the data need to be. For instance, are you testing the safety of a drug?   4.  Scale of measurements  (decide before doing experiment, so that you do not bias results) If you are measuring the rate of a response, you need to pick a reasonable time frame. For instance, copepods will respond fast (seconds),  while Isopods will respond slowly (minutes)   5.  Criteria for Accepting/Rejecting hypothesis  (decide before doing experiment, do not bias results); How big of a  difference do you need to see before you consider it a response?   6. Analysis of data See "Data Analysis" section below. You need to think about how you are going to analyze your data prior to starting your experiment.  
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Graphing Graphs are used to show trends, while Tables are used to show the exact value of something. Often, we (scientists) are more interested in  the trend in the data than the exact values of the data. A Graph illustrates a trend better than a Table. It is kind of like seeing a picture  of the Grand Canyon versus reading a description of it.   Procedures for Making Graphs 1. Put information on appropriate axis. X Axis = independent variable (what you manipulated goes on this axis) Y Axis = dependent variable (what you measured goes on this axis) For instance, if you measured meters of tree growth over years, then you will graph Growth (e.g., meter) on the y-axis and Time (e.g.,  years) on the x-axis. 2. Label both axes.
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This note was uploaded on 09/18/2008 for the course BIOL 1005 taught by Professor Ta during the Fall '07 term at LSU.

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Experimental Design - Experimental Design Once you have...

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