How to run Simple Linear Regression on SPSS

1. Running Simple Linear
Regression on SPSS
http://www.palmx.org/drtamil/spss/
sga-ttest-youtube.sav

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Factors Affecting SGA
SGA
(Y/N)
(Birth
weight)
Mother’s
Nutrition
(BMI/Obesity)
•Weight
•Height
Smoking
Hypertension

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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,

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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

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Factors Affecting SGA
Birth
weight
(in kg)
Proxy for
Mother’s
Nutrition; Body
Mass Index in
kg/m2
Smoking
(Y/N)
Hypertension
(Y/N)

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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.

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y = a + bx, “a” is y-intercept.

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y = a + bx, “b” is slope/steepness of line.

10. Running Simple Linear
Regression on SPSS
http://www.palmx.org/drtamil/spss/
sga-ttest-youtube.sav

11. ©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

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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.

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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.