Original Research

Application of statistical contrasts to mean refractive state

S Abelman
African Vision and Eye Health | South African Optometrist: Vol 65, No 1 | a250 | DOI: https://doi.org/10.4102/aveh.v65i1.250 | © 2006 S Abelman | This work is licensed under CC Attribution 4.0
Submitted: 19 December 2006 | Published: 19 December 2006

About the author(s)

S Abelman, Centre for Numerical Analysis and Computational Mathematics, School of Computational and Applied Mathematics, University of the Witwatersrand, Private Bag 3, Wits, 2050, South Africa

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Testing  for  differences  between  specific groups  or  combinations  of  groups  is  referred to as comparison or contrast testing. Statistical significance of comparisons can be assessed by first forming contrasts and then testing for their significance. A contrast essentially tests wheth-er or not two means are significantly different, where each mean could be a weighted average of two or more means. Gillan  investigated  whether  the  instillation of a cycloplegic (Mydriacyl 1% (tropicamide)) into the right eye of a 30-year-old female sub-ject would affect the variability of her distance refractive state as measured by an autorefractor.The  purpose  of  this  paper  is  to  introduce mutually orthogonal linear contrasts of sample data  to  optometric  research.  By  constructing particular contrasts, mean refractive states are compared  before  instillation,  before  and  after instillation, and after instillation.


Multiple comparisons, contrasts, hypothesis testing


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