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How to run Simple Linear Regression on SPSS

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How to run Simple Linear Regression on SPSS

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How to run Simple Linear Regression on SPSS

  1. 1. Running Simple Linear Regression on SPSS http://www.palmx.org/drtamil/spss/ sga-ttest-youtube.sav
  2. 2. ©drtamil@gmail.com 2016 Factors Affecting SGA SGA (Y/N) (Birth weight) Mother’s Nutrition (BMI/Obesity) •Weight •Height Smoking Hypertension
  3. 3. ©drtamil@gmail.com 2016 Dependent Outcome  Birth weight of the babies  Small for gestational age i.e. less than 2.7kg for term babies – Y/N By Yehudamalul - Own work, CC BY-SA 3.0,
  4. 4. ©drtamil@gmail.com 2016 What test to use?  Pearson’s Correlation done earlier showed that there is a significant positive and fair correlation between MOTHERS’ BODY MASS INDEX (in kg) and BIRTH WEIGHT (in kg)  Now model the relationship between MOTHERS’ BODY MASS INDEX (in kg) and BIRTH WEIGHT (in kg) by fitting a linear equation to observed data.  y = a + bx
  5. 5. ©drtamil@gmail.com 2016 Factors Affecting SGA Birth weight (in kg) Proxy for Mother’s Nutrition; Body Mass Index in kg/m2 Smoking (Y/N) Hypertension (Y/N)
  6. 6. ©drtamil@gmail.com 2016 What test to use?  Birth weight – interval/continuous data.  Body Mass Index – interval/continuous data.  The aim here to model the relationship between MOTHERS’ BODY MASS INDEX (in kg) and BIRTH WEIGHT (in kg) by fitting a linear equation to observed data.  Assuming both BMI & birth weight are normally distributed, most suitable test is Simple Linear Regression.
  7. 7. ©drtamil@gmail.com 2016 y = a + bx, “a” is y-intercept.
  8. 8. ©drtamil@gmail.com 2016 y = a + bx, “b” is slope/steepness of line.
  9. 9. Running Simple Linear Regression on SPSS http://www.palmx.org/drtamil/spss/ sga-ttest-youtube.sav
  10. 10. ©drtamil@gmail.com 2016 Results y = a + bx Birth weight = 1.524 + 0.053 mBMI For every increase of 1 unit of mother’s BMI, the baby’s birth weight increases 53 grams. Equation valid since p<0.05
  11. 11. ©drtamil@gmail.com 2016 Conclusion  Birth weight = 1.524 + 0.053 mBMI  For every increase of 1 unit of mother’s BMI, the baby’s birth weight increases 53 grams.  So if the mother’s BMI is 20, then the birth weight would be around: 1.524 + 0.053 x 20 = 2.584 kg  If the mother’s BMI is 40, then the birth weight would be around: 1.524 + 0.053 x 40 = 3.644 kg  r2 = 0.186, therefore 18.6% of the birth weight variability is contributed by mBMI.
  12. 12. ©drtamil@gmail.com 2016 Exercise  Repeat the same statistical test between; ◦ Mothers’ Weight and Birth Weight ◦ You can also swap Weight for Age or Height but take note of the p-values for a & b, some won’t be significant, indicating that the linear equation is not valid.

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