How to run Student's t-test on SPSS

1. Running Student’s
T-Test on SPSS
http://www.palmx.org/drtamil/spss/
sga-ttest-youtube.sav

2. ©drtamil@gmail.com 2016
Factors Affecting SGA
SGA
(Birth
weight)
Mother’s
Nutrition
(BMI/Obesity)
•Weight
•Height
Smoking
Hypertension

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,

5. ©drtamil@gmail.com 2016
What test to use?
 Conduct the appropriate statistical test to
test whether there is any association
between BMI and OUTCOME
(SGA/Normal).

6. ©drtamil@gmail.com 2016
Factors Affecting SGA
SGA
(Y/N)
(Birth
weight)
Mother’s
Nutrition
(BMI)
Smoking
(Y/N)
Hypertension
(Y/N)

7. ©drtamil@gmail.com 2016
Suitable statistical test?
 Body Mass Index – interval/continuous
data.
 Outcome is categorized into Yes (SGA
babies) and No (Normal babies)
Therefore it is categorical data.
 Basically we are comparing the mean
mothers’ BMI between SGA and normal
babies.
 Assuming BMI is normally distributed,
most suitable test is Student’s t-test.

8. ©drtamil@gmail.com 2016
Comparing BMI distribution

9. ©drtamil@gmail.com 2016
Comparing mean BMI
SGA
22.4 + 3.9
Normal
25.4 + 4.4

10. ©drtamil@gmail.com 2016
Which t & p-value to use?

11. ©drtamil@gmail.com 2016
t > than 1.96, p < than 0.05

12. ©drtamil@gmail.com 2016
Conclusion
 Mothers of SGA babies has clearly smaller
BMI (22.4 + 3.9) compared to mothers of
normal babies (25.4 + 4.4).
 The difference is statistically significant
since p value smaller than 0.05.
 Therefore mothers with lower BMI has a
significantly higher risk of getting SGA
babies compared to mothers with higher
BMI.
 “Big Mothers Get Big Babies!”

13. ©drtamil@gmail.com 2016
Exercise
 Repeat the same statistical test between;
◦ Weight and Outcome
◦ Height and Outcome