Biology Reference
In-Depth Information
TABLE 5.7 Likelihood Ratio Tests for the Two-Way Logistic Regression
Model Fitting Criteria
Likelihood Ratio Tests
Effect
e
2 Log Likelihood of Reduced Model
Chi-Square
df
Sig.
Intercept
183.2665
0
0
e
INA
238.2002
54.9337
5
0.00000
IOB
207.4619
24.1953
2
0.00001
NAW
193.9302
10.6637
2
0.00484
NBS
199.0345
15.7680
4
0.00335
PBD
191.4299
8.1634
2
0.01688
INA
¼
inferior nasal aperture
IOB
¼
interorbital breadth
NAW
¼
nasal aperture width
NBS
¼
nasal bone structure
PBD
¼
post-bregmatic depression
TABLE 5.8 Classification Matrix for Two-Way Logistic Regression
Black
White
% Correct
Black
200
17
92.17
White
19
117
86.03
Total
89.80
Logistic regression analysis can also be carried out in SPSS
using the NOMREG proce-
dure. We suggest a forward stepwise selection procedure. When we ran that analysis on
a sample of data collected by JTH (
2009
) the LR stepwise selected five variables: (1) inferior
nasal aperture, (2) interorbital breadth, (3) nasal aperture width, (4) nasal bone structure,
and (5) post-bregmatic depression. The likelihood ratio test (
Table 5.7
) is significant and
demonstrates that the reduced model is equivalent to the final LR model. The Cox and Snell
pseudo R-squared statistics (not shown) (0.553) imply that approximately 56% of the vari-
ation in morphoscopic trait expression is explained by ancestry. This LR model is accurate
for nearly 90% of the individuals in the sample (
Tabl e 5 . 8
).
Each of these presented methods has advantages and disadvantages and each is suited to
a particular task. We present these two statistics not to suggest they are the best or most appro-
priatemethods but todemonstrate the flexibility of statisticalmethods tohandle categorical data
and to encourage the reader to explore these and other statistics for use in their own projects.
CASE
STUDY: ASSESSING ANCESTRY FOR AN UNKN
OWN
In statistical models morphoscopic traits perform as well as a metric analysis (
Hefner 2007,
2009
). The following section guides the reader through a typical analysis of morphoscopic
traits, and presents reporting strategies to use following data analysis.
