Saturday, September 10, 2016

Impact of SAT scores and part-time students on university graduation rates

Impact of SAT scores and part-time students on university graduation rates

 A previous post showed that SAT scores had a 25% larger impact on on-time graduation rates for public universities than for private universities.


This post expands the model to also consider how part-time students impact the on-time graduation rate.


Question:   Add information on the percent of students attending a university part-time to the on-time graduation rate model.  Is an increase in the percent of students attending a university part-time related to the on-time graduation rate?   Does the inclusion of this information alter the impact of SAT scores on on-time graduation rates?

Analysis:   I follow the previous post and considered different models for private and public universities.   The regression coefficients for the two models are presented below. 


On-Time Graduation Rate Model Results
Public Universities
Private Universities
Coeff.
p-Value
Coeff.
p-Value
SAT Measure
0.011
0
0.010
0
Part Time Student %
-1.549
0.197
0.816
0.315
Constant
-5.253
0
-5.179
0
Sample Size
31
20
R2
86.7
84.4


Observations:

The SAT Measure remains highly significantly related to on-time graduation rates for both private and public universities


The variable percent of students attending a university part time is not significantly related to on-time graduation rates for either public or private universities.

The coefficient of the SAT Measure in the public university model is 5.7% higher than the coefficient of the SAT Measure in the private university model.   (This differential was much larger (around 25%) when the part-time percentage variable was excluded from the model.   See previous post on this.)


Comments:

The part-time percentage variable is not significant but its inclusion in the model has a large impact on the differential between the impact of SAT Scores on graduation rates in public versus private universities.


The sample sizes (31) for public universities and (20) for private universities are too small.   To paraphrase the movie Jaws I need a bigger boat.


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