Experimental planning


When you are preparing to initiate an experimental program, be sure to question yourself and others to help guide your progress. The following questions will help you dig deeper into your project.

  • Why perform the experiments?
  • Can the information you are seeking be found elsewhere (such as literature journals, books, company reports, etc.)?
  • Can you do some calculations instead?
  • Have sufficient time and money been budgeted for the program?
  • Are you restricted to specific materials or equipment?
  • Will the safety of the investigators be endangered to such a degree that the program should not be carried out?

These and other appropriate questions must be answered prior to beginning the experimental program so that the need for the experiments is clearly established.

Define the Objectives of the Experiment

Prepare a list of all the things you want to accomplish. Next try to prioritize your list, keeping in mind the following:

  • What questions regarding your problem would you most like to answer?
  • Are you sure you are not losing sight of the overall objectives and other possible alternative solutions ("can't see the forest for the trees" syndrome)?
  • How comprehensive does the program need to be? Are you looking at an exhaustive study or a cursory examination of a narrow set of conditions?

Specific answers to these questions will guide the rest of the project.

Choose the Responses You Want to Measure

There are generally two different types of variables that are considered in an experimental program. The independent variables make things happen. Changes in the independent variables cause the system to respond. The responses are the dependent variables. Changing any one of the independent variables will change the system response (the dependent variable). As the experimental program is designed, the important dependent variables to be measured must be identified.

  • What are the controlled or independent variables?
  • What are the dependent variables?
  • Are instruments or techniques available to make the measurements?
  • Do they need to be calibrated? If so, have they been?
  • Will the accuracy and precision of the expected results be sufficient to distinguish between different theories or possible outcomes?

In any experimental program there will always be many, many quantities you can measure. However, you must decide which independent variables have the greatest influence on the dependent variable.

  • What are the really important measurements to make?
  • What are the ranges or levels of these variables to be examined?
  • Instead of changing each independent variable separately, can dimensionless ratios or groups be formed and varied so as to produce the same end results with fewer measurements?

Experimental planning

To obtain the maximum benefit from a series of experiments, they must be properly designed. How can the experimental program be designed to achieve the experimental objectives in the simplest manner with the minimum number of measurements and the least expense? A successfully designed experiment is a series of organized trials which enables one to obtain the most experimental information with the least amount of effort. Three important questions to consider when designing experiments are:

· What are the types of errors to avoid?

· What is the minimum number of experiments that must be performed?

· When should we consider repeating experiments?