The Bayley Scales of Infant Development yield score on two indices – the Psychom

Question

The Bayley Scales of Infant Development yield score on two indices – the Psychomotor Development Index (PDI) and the Mental Development Index (MDI) – that can be used to assess a child’s level of functioning at approximately one year of age. As part of a study investigation the development and neurologic status of children who had undergone reparative heart surgery during the first three months of life, the Bayley Scales were administered to a sample of one-year-old infants born with congenital heart disease. The children had been randomized to one of two different treatment groups, known as “circulatory arrest” and “low-flow bypass”. The groups differed in the specific way the surgery was performed. Unlike circulatory arrest, low-flow bypass maintains continuous circulation through the brain. Although it is felt to be preferable by some physicians, it has its own risks of brain injury. The data for this study are saved in the dataset heart (.xls or .csv) (included in the materials provided). The PDI scores are saved under the variable pdi and the MDI scores under the variable mdi, and indicators of treatment group under trtment (0=circulatory arrest, 1=low-flow bypass)      

a) At the 0.05 level of significance, test the null hypothesis that the mean PDI score at one year of age for
the circulatory arrest group is equal to the mean PDI score for the low-flow group. What is the p-value?
b) At the 0.05 level of significance, test the null hypothesis that the mean MDI score at one year of age for
the circulatory arrest group is equal to the mean MDI score for the low-flow group. What is the p-value?
c) What to these tests suggest about the relationship between a child’s surgical treatment and his/her
subsequent developmental status at one year of age?              

trtment pdi mdi 0 80 74 1 118 124 1 122 109 0 98 78 0 98 91 0 111 130 1 111 119 1 0 82 115 1 99 112 0 86 119 1 92 100 0 122 115 1 98 117 0 78 108 0 92 115 0 86 112 1 90 82 0 92 142 0 104 102 1 92 130 0 105 103 1 98 93 1 80 96 1 50 50 1 87 112 0 67 106 1 80 93 0 76 110 1 98 117 1 98 96 1 92 126 0 80 91 1 98 106 0 86 91 1 92 117 0 86 91 1 105 86 1 115 118

Explanation / Answer

A. p value is 0.28(>0.05) which suggests that the mean value of PDI for circulatory arrest group is equal to that of low flow group. The two tailed t test was conducted in excel using function t.test

B.p value is 0.997 suggests that mean value of MDI for circulatory arrest group is equal to that of low flow group

C. These tests suggests that the surgery has no role in the MDI or PDI for the two different categorization group i.e circulatory arrest and low inflow bypass

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