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Experimental design

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  • 1. BY: LIPSA RAY MARIE ARBUDA LINGARAJ MALLICK
  • 2. Introduction:  A survey among statisticians employed by different national authorities to find out what they understand under the term “experimental design” would elicit a variety of different replies. The purpose of the introduction is to explain as many aspects of statistical experimental design as possible while trying to avoid formal definition such as;  “Experimental design is a specific form of statistical decision making problem”
  • 3.  Experimental design is a planned interference in the natural order of events by the researcher. He does something more than carefully observe what is occurring  This emphasis on experiment reflects the higher regard generally given to information so derived  There is good rationale for this. Much of the substantial gain in knowledge in all sciences has come from actively manipulating or interfering with the stream of events  There is more than just observation or measurement of a natural event  A selected condition or a change (treatment) is introduced. Observations or measurements are planned to illuminate the effect of any change in conditions
  • 4. POSTULATES  POSTULATE-I: An appropriate experimental design can be selected only if the question to be answered by the experiment is defined as closely as possible  POSTULATE-II:The closer definition of the experimental question must include selection of the model and specification of accuracies
  • 5. DEFINITION:  A statistical experimental design or an experimental design is a set of rules for performing a statistical experiment in which aspects having no bearing on the analysis of the experiment and not being taken into account in the model ignored
  • 6. PRINCIPLES OF EXPERIMENTAL DESIGN:  Principle of replication  Principle of randomization  Principle of local control
  • 7. •INFORMAL DESIGN •FORMAL DESIGN TYPES OF EXPERIMENTAL DESIGN
  • 8.  COMPLETELY RANDOMIZED DESIGN (CR DESIGN)  RANDOMIZED BLOCK DESIGN (RB DESIGN)
  • 9.  In a completely randomized design, objects or subjects are assigned to groups completely at random. One standard method for assigning subjects to treatment groups is to label each subject, then use a table of random numbers to select from the labelled subjects. This may also be accomplished using a computer.  It involves only two principle viz ; the principle of replication and randomization  It is generally used when experimental areas happen to be homogenous  Technically, when all the variations due to uncontrolled extraneous factors are included under the heading of chance variation , we refer to the design of experiment as CR Design
  • 10.  If an experimenter is aware of specific differences among groups of subjects or objects within an experimental group, he or she may prefer a randomized block design to a completely randomized design.  In a block design, experimental subjects are first divided into homogeneous blocks before they are randomly assigned to a treatment group.  If, for instance, an experimenter had reason to believe that age might be a significant factor in the effect of a given medication, he might choose to first divide the experimental subjects into age groups, such as under 30 years old, 30-60 years old, and over 60 years old.  Then, within each age level, individuals would be assigned to treatment groups using a completely randomized design. In a block design, both control and randomization are considered.  It is an improvement over the CR design.  In the RB design the principle of local control can be applied along with the other two principles
  • 11. LATIN SQUARE DESIGN : (LS DESIGN)  It is used in agricultural research . The treatment in a LS design are also allocated among the plots that no treatment occurs more than once in any row or column
  • 12.  It is used in experiments where the effects of varying more than one factor are to be determined.  They are especially important in several economic and social phenomena where usually a large number of factors affect a particular problem
  • 13.  Researchers are rarely satisfied to simply describe the events they observe. They want to make inferences about what produced, contributed to, or caused events. To gain such information without ambiguity, some form of experimental design is ordinarily required.  As a consequence, the need for using rather elaborate designs ensues from the possibility of alternative relationships, consequences or causes. The purpose of the design is to rule out these alternative causes, leaving only the actual factor that is the real cause.
  • 14. CONCLUSION  There are several research designs and the researcher must decide in advance of collection and analysis of data as to which design would prove to be more appropriate for his research project . He must give due weight to various points such as  Type of Universe and its nature  Objective of his study  Resource list(sample frame)  Desired standard of accuracy
  • 15. HAVE A NICE DAY

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