Lesson 13: Cross-over Repeated Measure Designs

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Key Learning Goals for this Lesson:
  • Recognition of cross-over repeated measures designs
  • Understand what a wash-out period is and the potential for carry-over effects
  • General understanding about how to adjust treatment means for the presence of carry-over effects
  • General understanding about how to test for the significance of carry-over effects.

The Cross-over design is briefly discussed Section 28.8, pages 564-567 of the textbook.  This is a very advanced topic in ANOVA, which we provide some exposure to in this lesson.  However this topic is covered in much more detail in Experimental Design (STAT 503).  Our objective for this lesson is to provide some familiarity with the topic.  Unlike other foundational aspects of this course, it is assumed that this introductory material will be elaborated on in further courses. 

Consistent with the learning objectives for this unit, the expectation is that students can recognize and understand in theory, how to test for and adjust for carry over.  Again, the refinement of this knowledge is left for a subsequent course.

When experimental units over time are given each of the treatment levels, then we have a cross-over design, a special case of repeated measures.

In ordinary repeated measures we are simply looking at multiple (repeat) measurements on the experimental units through time, having been assigned to receive a treatment level. Here, we have sequences of applications of treatments over time wherein experimental units are given each of the treatment levels in an ordered sequence.