Logistic regression
Recall the simple linear regression model:
y = 0 + 1x +
where we are trying to predict a continuous dependent variable y from a continuous independent variable x.
This model can be extended to Multiple linear regression model:
y = 0 + 1x1 + 2x2 + … + + pxp + Here we are trying to predict a continuous dependent variable y from a several continuous dependent variables x1 , x2 , … , xp .
Now suppose the dependent variable y is binary.
It takes on two values “Success” (1) or “Failure” (0)
This is the situation in which Logistic Regression is used
We are interested in predicting a y from a continuous dependent variable x.
Example
We are interested how the success (y) of a new antibiotic cream is curing “acne problems” and how it depends on the amount (x) that is applied daily.
The values of y are 1 (Success) or 0 (Failure).
The values of x range over a continuum
The logisitic Regression ModelLet p denote P[y = 1] = P[Success].
This quantity will increase with the value of x.
The ratio: 1
p
pis called the odds ratio
This quantity will also increase with the value of x, ranging from zero to infinity.
The quantity: ln1
p
p
is called the log odds ratio
Example: odds ratio, log odds ratio
Suppose a die is rolled:Success = “roll a six”, p = 1/6
1 16 6
516 6
1
1 1 5
p
p
The odds ratio
1ln ln ln 0.2 1.69044
1 5
p
p
The log odds ratio
The logisitic Regression Model
i. e. :
0 1
1xp
ep
In terms of the odds ratio
0 1ln1
px
p
Assumes the log odds ratio is linearly related to x.
The logisitic Regression Model
0 1
1xp
ep
or
Solving for p in terms x.
0 1 1xp e p
0 1 0 1x xp pe e
0 1
0 11
x
x
ep
e
0
0.2
0.4
0.6
0.8
1
0 2 4 6 8 10
Interpretation of the parameter 0
(determines the intercept)
p
0
01
e
e
x
0
0.2
0.4
0.6
0.8
1
0 2 4 6 8 10
Interpretation of the parameter 1
(determines when p is 0.50 (along with 0))
p 0 1
0 1
1 1
1 1 1 2
x
x
ep
e
x
00 1
1
0 or x x
when
Also0 1
0 11
x
x
dp d e
dx dx e
0
1
x
when
0 1 0 1 0 1 0 1
0 1
1 1
2
1
1
x x x x
x
e e e e
e
0 1
0 1
1 12 41
x
x
e
e
1
4
is the rate of increase in p with respect to x when p = 0.50
0
0.2
0.4
0.6
0.8
1
0 2 4 6 8 10
Interpretation of the parameter 1
(determines slope when p is 0.50 )
p
x
1slope 4
The data
The data will for each case consist of
1. a value for x, the continuous independent variable
2. a value for y (1 or 0) (Success or Failure)
Total of n = 250 cases
case x y
1 0.8 02 2.3 13 2.5 04 2.8 15 3.5 16 4.4 17 0.5 08 4.5 19 4.4 110 0.9 011 3.3 112 1.1 013 2.5 114 0.3 115 4.5 116 1.8 017 2.4 118 1.6 019 1.9 120 4.6 1
case x y
230 4.7 1231 0.3 0232 1.4 0233 4.5 1234 1.4 1235 4.5 1236 3.9 0237 0.0 0238 4.3 1239 1.0 0240 3.9 1241 1.1 0242 3.4 1243 0.6 0244 1.6 0245 3.9 0246 0.2 0247 2.5 0248 4.1 1249 4.2 1250 4.9 1
Estimation of the parameters
The parameters are estimated by Maximum Likelihood estimation and require a statistical package such as SPSS
Using SPSS to perform Logistic regression
Open the data file:
Choose from the menu:
Analyze -> Regression -> Binary Logistic
The following dialogue box appears
Select the dependent variable (y) and the independent variable (x) (covariate).
Press OK.
Here is the output
The Estimates and their S.E.
The parameter Estimates
SE
X 1.0309 0.1334Constant -2.0475 0.332
1 1.03090 -2.0475
Interpretation of the parameter 0
(determines the intercept)
0
0
-2.0475
-2.0475intercept 0.1143
1 1
e e
e e
Interpretation of the parameter 1
(determines when p is 0.50 (along with 0))
0
1
2.04751.986
1.0309x
Another interpretation of the parameter 1
1
4
is the rate of increase in p with respect to x when p = 0.50
1 1.03090.258
4 4
The Multiple Logistic Regression model
Here we attempt to predict the outcome of a binary response variable Y from several independent variables X1, X2 , … etc
0 1 1ln1 p p
pX X
p
0 1 1
0 1 1 or
1
p p
p p
X X
X X
ep
e
Multiple Logistic Regression an example
In this example we are interested in determining the risk of infants (who were born prematurely) of developing BPD (bronchopulmonary dysplasia)
More specifically we are interested in developing a predictive model which will determine the probability of developing BPD from
X1 = gestational Age and X2 = Birthweight
For n = 223 infants in prenatal ward the following measurements were determined
1. X1 = gestational Age (weeks),
2. X2 = Birth weight (grams) and3. Y = presence of BPD
The datacase Gestational Age Birthweight presence of BMD
1 28.6 1119 12 31.5 1222 03 30.3 1311 14 28.9 1082 05 30.3 1269 06 30.5 1289 07 28.5 1147 08 27.9 1136 19 30 972 0
10 31 1252 011 27.4 818 012 29.4 1275 013 30.8 1231 014 30.4 1112 015 31.1 1353 116 26.7 1067 117 27.4 846 118 28 1013 019 29.3 1055 020 30.4 1226 021 30.2 1237 022 30.2 1287 023 30.1 1215 024 27 929 125 30.3 1159 026 27.4 1046 1
The resultsVariables in the Equation
-.003 .001 4.885 1 .027 .998
-.505 .133 14.458 1 .000 .604
16.858 3.642 21.422 1 .000 2.1E+07
Birthweight
GestationalAge
Constant
Step1
a
B S.E. Wald df Sig. Exp(B)
Variable(s) entered on step 1: Birthweight, GestationalAge.a.
ln 16.858 .003 .5051
pBW GA
p
16.858 .003 .505
1BW GAp
ep
16.858 .003 .505
16.858 .003 .5051
BW GA
BW GA
ep
e
Graph: Showing Risk of BPD vs GA and BrthWt
0
0.2
0.4
0.6
0.8
1
700 900 1100 1300 1500 1700
GA = 27
GA = 28
GA = 29
GA = 30
GA = 31
GA = 32
Discrete Multivariate Analysis
Analysis of Multivariate Categorical Data
Example 1
Data Set #1 - A two-way frequency table Serum Systolic Blood pressure
Cholesterol <127 127-146 147-166 167+ Total <200 117 121 47 22 307 200-219 85 98 43 20 246 220-259 119 209 68 43 439 260+ 67 99 46 33 245 Total 388 527 204 118 1237
In this study we examine n = 1237 individuals measuring X, Systolic Blood Pressure and Y, Serum Cholesterol
Example 2
The following data was taken from a study of parole success involving 5587 parolees in Ohio between 1965 and 1972 (a ten percent sample of all parolees during this period).
The study involved a dichotomous response Y– Success (no major parole violation) or – Failure (returned to prison either as technical
violators or with a new conviction)
based on a one-year follow-up.
The predictors of parole success included are: 1. type of committed offence (Person offense or
Other offense), 2. Age (25 or Older or Under 25), 3. Prior Record (No prior sentence or Prior
Sentence), and 4. Drug or Alcohol Dependency (No drug or
Alcohol dependency or Drug and/or Alcohol dependency).
• The data were randomly split into two parts. The counts for each part are displayed in the table, with those for the second part in parentheses.
• The second part of the data was set aside for a validation study of the model to be fitted in the first part.
Table
No drug or alcohol dependency Drug and/or alcohol dependency 25 or older Under 25 25 or Older Under 25 Person
offense Other
offense Person offense
Other offense
Person offense
Other offense
Person offense
Other offense
No prior Sentence of Any Kind Success 48 34 37 49 48 28 35 57 (44) (34) (29) (58) (47) (38) (37) (53) Failure 1 5 7 11 3 8 5 18 (1) (7) (7) (5) (1) (2) (4) (24) Prior Sentence Success 117 259 131 319 197 435 107 291 (111) (253) (131) (320) (202) (392) (103) (294) Failure 23 61 20 89 38 194 27 101 (27) (55) (25) (93) (46) (215) (34) (102)
Analysis of a Two-way Frequency Table:
Frequency Distribution (Serum Cholesterol and Systolic Blood Pressure)
Serum Systolic Blood pressure Cholesterol <127 127-146 147-166 167+ Total
<200 117 121 47 22 307 200-219 85 98 43 20 246 220-259 119 209 68 43 439
260+ 67 99 46 33 245 Total 388 527 204 118 1237
Joint and Marginal Distributions (Serum Cholesterol and Systolic Blood Pressure)
Serum Systolic Blood pressure Marginal distn Cholesterol <127 127-146 147-166 167+ (Serum Chol.)
<200 9.46 9.78 3.80 1.78 24.82 200-219 6.87 7.92 3.48 1.62 19.89 220-259 9.62 16.90 5.50 3.48 35.49
260+ 5.42 8.00 3.72 2.67 19.81 Marginal distn (BP)
31.37 42.60 16.49 9.54 100.00
The Marginal distributions allow you to look at the effect of one variable, ignoring the other. The joint distribution allows you to look at the two variables simultaneously.
Conditional Distributions ( Systolic Blood Pressure given Serum Cholesterol )
The conditional distribution allows you to look at the effect of one variable, when the other variable is held fixed or known.
Serum Systolic Blood pressure Cholesterol <127 127-146 147-166 167+ Total
<200 38.11 39.41 15.31 7.17 100.00 200-219 34.55 39.84 17.48 8.13 100.00 220-259 27.11 47.61 15.49 9.79 100.00
260+ 27.35 40.41 18.78 13.47 100.00 Marginal distn (BP)
31.37 42.60 16.49 9.54 100.00
Conditional Distributions
(Serum Cholesterol given Systolic Blood Pressure)
Serum Systolic Blood pressure Marginal distn Cholesterol <127 127-146 147-166 167+ (Serum Chol.)
<200 30.15 22.96 23.04 18.64 24.82 200-219 21.91 18.60 21.08 16.95 19.89 220-259 30.67 39.66 33.33 36.44 35.49
260+ 17.27 18.79 22.55 27.97 19.81 Total 100.00 100.00 100.00 100.00 100.00
GRAPH: Conditional distributions of Systolic Blood Pressure given Serum Cholesterol
127-146 147-166<127 167+
SYSTOLIC BLOOD PRESSURE
<200
200-219
260+
220-259
Marginal Distribution
SERUM CHOLESTEROL
40%
50%
30%
20%
10%
Notation:
Let xij denote the frequency (no. of cases) where X (row variable) is i and Y (row variable) is j.
1
c
i i ijj
x R x
1
r
j j iji
x C x
1 1 1 1
r c r c
ij i ji j i j
x N x x x
Different Models
,ij P X i Y j
11 1211 12 11 12
11
, , , rcxx xrc rc
rc
Nf x x x
x x
The Multinomial Model:
Here the total number of cases N is fixed and xij follows a multinomial distribution with parameters ij
11 1211 12
11
!
! !rcxx x
rcrc
N
x x
ij ij ijE x N
11 1211 12 1| 2| |
1 1
, , , ic
ri xx x
rc i i c ii i ic
Rf x x x
x x
The Product Multinomial Model:
Here the row (or column) totals Ri are fixed and for a given row i, xij follows a multinomial distribution with parameters j|i
|ij ij i j iE x R
11 121 1
, , ,!
ij
ij
xr cij
rci j ij
f x x x ex
The Poisson Model:
In this case we observe over a fixed period of time and all counts in the table (including Row, Column and overall totals) follow a Poisson distribution. Let ij denote the mean of xij.
ij ijE x
!
ij
ij
xij
ij ijij
f x ex
Independence
Multinomial Model
,ij P X i Y j P X i P Y j
i j
ij ij i jN N
if independent
and
The estimated expected frequency in cell (i,j) in the case of independence is:
ˆ ˆ ˆ jiij ij i j
xxm N N
N N
i j i jx x R C
N N
The same can be shown for the other two models – the Product Multinomial model and the Poisson model
namely
The estimated expected frequency in cell (i,j) in the case of independence is:
ˆ i j i jij ij
R C x xm
N x
Standardized residuals are defined for each cell:
ij ijij
ij
x mr
m
The Chi-Square Statistic
2
2 2
1 1 1 1
r c r cij ij
iji j i j ij
x mr
m
The Chi-Square test for independence
Reject H0: independence if
2
2 2/ 2
1 1
1 1r c
ij ij
i j ij
x mdf r c
m
TableExpected frequencies, Observed frequencies,
Standardized Residuals
Serum Systolic Blood pressure Cholesterol <127 127-146 147-166 167+ Total
<200 96.29 130.79 50.63 29.29 307 (117) (121) (47) (22) 2.11 -0.86 -0.51 -1.35
200-219 77.16 104.80 40.47 23.47 246 (85) (98) (43) (20) 0.86 -0.66 0.38 -0.72
220-259 137.70 187.03 72.40 41.88 439 (119) (209) (68) (43) -1.59 1.61 -0.52 0.17
260+ 76.85 104.38 40.04 23.37 245 (67) (99) (46) (33) -1.12 -0.53 0.88 1.99
Total 388 527 204 118 1237 2 = 20.85 (p = 0.0133)
Example
In the example N = 57,407 cases in which individuals were victimized twice by crimes were studied.
The crime of the first victimization (X) and the crime of the second victimization (Y) were noted.
The data were tabulated on the following slide
Table 1: Frequencies
Second Victimization in Pair Ra A Ro PP/PS PL B HL MV Total Ra 26 50 11 6 82 39 48 11 273 A 65 2997 238 85 2553 1083 1349 216 8586
First Ro 12 279 197 36 459 197 221 47 1448 Victimization PP/PS 3 102 40 61 243 115 101 38 703
in pair PL 75 2628 413 229 12137 2658 3689 687 22516 B 52 1117 191 102 2649 3210 1973 301 9595 HL 42 1251 206 117 3757 1962 4646 391 12372 MV 3 221 51 24 678 301 367 269 1914 Total 278 8645 1347 660 22558 9565 12394 1960
Table 2: Standardized residuals
Second Victimization in Pair Ra A Ro PP/PS PL B HL MV Ra 21.5 1.4 1.8 1.6 -2.4 -1.0 -1.9 0.6 A 3.6 47.4 2.6 -1.4 -14.1 -9.2 -11.7 -4.5
First Ro 1.9 4.1 28.0 4.7 -4.6 -2.8 -5.2 -0.3 Victimization PP/PS -0.2 -0.4 5.8 18.6 -2.0 -0.2 -4.1 2.9
in pair PL -3.3 -13.1 -5.0 -1.9 35.0 -17.9 -16.8 -2.9 B 0.8 -8.6 -2.3 -0.8 -18.3 40.3 -2.2 -1.5 HL -2.3 -14.2 -4.9 -2.1 -15.8 -2.2 38.2 -1.5 MV -2.1 -4.0 0.9 0.4 -2.7 -1.0 -2.3 25.2
11,430 (highly significant)
Table 3: Conditional distribution of second victimization given the first victimization (%)
Second Victimization in Pair Ra A Ro PP/PS PL B HL MV Ra 9.5 18.3 4.0 2.2 30.0 14.3 17.6 4.0 100.0 A 0.8 34.9 2.8 1.0 29.7 12.6 15.7 2.5 100.0
First Ro 0.8 19.3 13.6 2.5 31.7 13.6 15.3 3.2 100.0 Victimization PP/PS 0.4 14.5 5.7 8.7 34.6 16.4 14.4 5.4 100.0
in pair PL 0.3 11.7 1.8 1.0 53.9 11.8 16.4 3.1 100.0 B 0.5 11.6 2.0 1.1 27.6 33.5 20.6 3.1 100.0 HL 0.3 10.1 1.7 0.9 30.4 15.9 37.6 3.2 100.0 MV 0.2 11.5 2.7 1.3 35.4 15.7 19.2 14.1 100.0
Marginal 0.5 15.1 2.3 1.1 39.3 16.7 21.6 3.4 100.0
Log Linear Model
Recall, if the two variables, rows (X) and columns (Y) are independent then
ij ij i jN N
and
ln ln ln lnij i jN
In general let
1( ) 2( ) 12( , )ln ij i j i ju u u u
1ln ij
i j
urc
1( )
1lni ij
j
u uc
2( )
1lnj ij
i
u ur
12( , ) 1( ) 2( )lni j ij i ju u u u
then
where1( ) 2( ) 12( , ) 12( , ) 0i j i j i j
i j i j
u u u u
(1)
Equation (1) is called the log-linear model for the frequencies xij.
Note: X and Y are independent if
1( ) 2( )ln ij i ju u u
In this case the log-linear model becomes
12( , ) 0 for all ,i ju i j
Three-way Frequency Tables
ExampleData from the Framingham Longitudinal Study of Coronary Heart Disease (Cornfield [1962])
Variables
1. Systolic Blood Pressure (X)– < 127, 127-146, 147-166, 167+
2. Serum Cholesterol– <200, 200-219, 220-259, 260+
3. Heart Disease– Present, Absent
The data is tabulated on the next slide
Three-way Frequency Table
Coronary Heart
Serum Cholesterol
Systolic Blood pressure (mm Hg)
Disease (mm/100 cc) <127 127-146 147-166 167+ <200 2 3 3 4
Present 200-219 3 2 0 3 220-259 8 11 6 6 260+ 7 12 11 11 <200 117 121 47 22
Absent 200-219 85 98 43 20 220-259 119 209 68 43 260+ 67 99 46 33
Log-Linear model for three-way tables
Let ijk denote the expected frequency in cell (i,j,k) of the table then in general
1( ) 2( ) 3( ) 12( , )ln ij i j k i ju u u u u
1( ) 2( ) 3( ) 12( , ) 12( , )0 i j k i j i ji j k i j
u u u u u
13( , ) 23( , ) 123( , , )i k j k i j ku u u where
13( , ) 13( , ) 23( , ) 23( , )i k i k j k j ki k j k
u u u u 123( , , ) 123( , , ) 123( , , )i j k i j k i j k
i j k
u u u
Hierarchical Log-linear models for categorical Data
For three way tables
The hierarchical principle:
If an interaction is in the model, also keep lower order interactions and main effects associated with that interaction
1.Model: (All Main effects model)
ln ijk = u + u1(i) + u2(j) + u3(k)
i.e. u12(i,j) = u13(i,k) = u23(j,k) = u123(i,j,k) = 0.
Notation:
[1][2][3]
Description:
Mutual independence between all three variables.
2.Model:
ln ijk = u + u1(i) + u2(j) + u3(k) + u12(i,j)
i.e. u13(i,k) = u23(j,k) = u123(i,j,k) = 0.
Notation:
[12][3]
Description:
Independence of Variable 3 with variables 1 and 2.
3.Model:
ln ijk = u + u1(i) + u2(j) + u3(k) + u13(i,k)
i.e. u12(i,j) = u23(j,k) = u123(i,j,k) = 0.
Notation:
[13][2]
Description:
Independence of Variable 2 with variables 1 and 3.
4.Model:
ln ijk = u + u1(i) + u2(j) + u3(k) + u23(j,k)
i.e. u12(i,j) = u13(i,k) = u123(i,j,k) = 0.
Notation:
[23][1]
Description:
Independence of Variable 3 with variables 1 and 2.
5.Model:
ln ijk = u + u1(i) + u2(j) + u3(k) + u12(i,j) + u13(i,k)
i.e. u23(j,k) = u123(i,j,k) = 0.
Notation:
[12][13]
Description:
Conditional independence between variables 2 and 3 given variable 1.
6.Model:
ln ijk = u + u1(i) + u2(j) + u3(k) + u12(i,j) + u23(j,k)
i.e. u13(i,k) = u123(i,j,k) = 0.
Notation:
[12][23]
Description:
Conditional independence between variables 1 and 3 given variable 2.
7.Model:
ln ijk = u + u1(i) + u2(j) + u3(k) + u13(i,k) + u23(j,k)
i.e. u12(i,j) = u123(i,j,k) = 0.
Notation:
[13][23]
Description:
Conditional independence between variables 1 and 2 given variable 3.
8.Model:
ln ijk = u + u1(i) + u2(j) + u3(k) + u12(i,j) + u13(i,k) + u23(j,k)
i.e. u123(i,j,k) = 0.Notation:
[12][13][23] Description:Pairwise relations among all three variables, with each two variable interaction unaffected by the value of the third variable.
9.Model: (the saturated model)
ln ijk = u + u1(i) + u2(j) + u3(k) + u12(i,j) + u13(i,k) + u23(j,k) + u123(i,j,k)
Notation:
[123]
Description:
No simplifying dependence structure.
Hierarchical Log-linear models for 3 way table
Model Description
[1][2][3] Mutual independence between all three variables.
[1][23] Independence of Variable 1 with variables 2 and 3.
[2][13] Independence of Variable 2 with variables 1 and 3.
[3][12] Independence of Variable 3 with variables 1 and 2.
[12][13] Conditional independence between variables 2 and 3 given variable 1.
[12][23] Conditional independence between variables 1 and 3 given variable 2.
[13][23] Conditional independence between variables 1 and 2 given variable 3.
[12][13] [23] Pairwise relations among all three variables, with each two variable interaction unaffected by the value of the third variable.
[123] The saturated model
Maximum Likelihood Estimation
Log-Linear Model
For any Model it is possible to determine the maximum Likelihood Estimators of the parameters
Example
Two-way table – independence – multinomial model
11 1211 12 11 12
11
, , , rcxx xrc rc
rc
Nf x x x
x x
11 12
11 12
11
!
! !
rcxx x
rc
rc
N
x x N N N
ij ij ijE x N orij
ij N
Log-likelihood
11 12, , ln ! ln !rc iji j
l N x
ln lnij ij iji j i j
N x x lnij ij
i j
K x where ln ! ln ! lnij
i j
K N x N N
1 2ln ij i ju u u
With the model of independence
and
1 1 1 2 1 2, , , , , ,c rl u u u u u K
1 2ij i ji j
x u u u
with 1 2 0i ji j
u u
1 2i ji ji j
K Nu x u x u
1 2 1 2i j i ju u u u uuij
i j i j i j
e e e e N
also
Let
1 2 21 1 1 2 1 2, , , , , , , , ,c rg u u u u u
1 2
1 11 2i ju uu
i ji j i j
u u e e e N
1 2i ji ji j
K Nu x u x u
Now
1 2 1 0i ju uu
i j
gN e e e N
u
1
1 2
1
1
i ju uui
ji
gx e e e
u
1
11 0
i
i
u
i u
i
ex N
e
1
1
1i
i
u
i iu
i
x xe
N Ne
1 111 and 0
ii i
i
xx
rN N N
Since
Now 1
1iu
ie x K
or 11 ln lniiu x K
11 ln ln 0iii i
u x r K
Hence
1
1ln lni ii
i
u x xr
1
1ln ln i
i
K xr
and
2
1ln lnj jj
i
u x xc Similarly
1 2 1 2i j i ju u u u uuij
i j i j i j
e e e e N
Finally
Hence
2
1
1
ju j
c c
jj
xe
x
Now
1 2i j
uu u
i j
Ne
e e
and
1
1
1
iu i
r r
ii
xe
x
11
1 1
r c cru
i ji ji j
i j
Ne x x
x x
11
1 1
1 r c cr
i ji j
x xN
Hence
Note
1 1ln ln lni j
i j
u x x Nr c
1 2ln ij i ju u u 1 1
ln ln lni ji j
x x Nr c
1 1ln ln ln lni i j j
i i
x x x xr c
ln ln lni jN x x
or i jij
x x
N
Comments
• Maximum Likelihood estimates can be computed for any hierarchical log linear model (i.e. more than 2 variables)
• In certain situations the equations need to be solved numerically
• For the saturated model (all interactions and main effects), the estimate of ijk… is xijk… .
Goodness of Fit Statistics
These statistics can be used to check if a log-linear model will fit the
observed frequency table
Goodness of Fit StatisticsThe Chi-squared statistic
2
2 Observed Expected
Expected
The Likelihood Ratio statistic:
2 2 ln 2 lnˆ
ijkijk
ijk
xObservedG Observed x
Expected
d.f. = # cells - # parameters fitted
2ˆ
ˆijk ijk
ijk
x
We reject the model if 2 or G2 is greater than2
/ 2
Example: Variables
Coronary Heart
Serum Cholesterol
Systolic Blood pressure (mm Hg)
Disease (mm/100 cc) <127 127-146 147-166 167+ <200 2 3 3 4
Present 200-219 3 2 0 3 220-259 8 11 6 6 260+ 7 12 11 11 <200 117 121 47 22
Absent 200-219 85 98 43 20 220-259 119 209 68 43 260+ 67 99 46 33
1. Systolic Blood Pressure (B)Serum Cholesterol (C)Coronary Heart Disease (H)
MODEL DF LIKELIHOOD- PROB. PEARSON PROB. RATIO CHISQ CHISQ ----- -- ----------- ------- ------- ------- B,C,H. 24 83.15 0.0000 102.00 0.0000 B,CH. 21 51.23 0.0002 56.89 0.0000 C,BH. 21 59.59 0.0000 60.43 0.0000 H,BC. 15 58.73 0.0000 64.78 0.0000 BC,BH. 12 35.16 0.0004 33.76 0.0007 BH,CH. 18 27.67 0.0673 26.58 0.0872 n.s. CH,BC. 12 26.80 0.0082 33.18 0.0009 BC,BH,CH. 9 8.08 0.5265 6.56 0.6824 n.s.
Goodness of fit testing of Models
Possible Models:1. [BH][CH] – B and C independent given H.2. [BC][BH][CH] – all two factor interaction model
Model 1: [BH][CH] Log-linear parameters
Heart disease -Blood Pressure Interaction
Bp Hd <127 127-146 147-166 167+ Pres -0.256 -0.241 0.066 0.431 Abs 0.256 0.241 -0.066 -0.431
,HB i ju
Bp Hd <127 127-146 147-166 167+ Pres -2.607 -2.733 0.660 4.461 Abs 2.607 2.733 -0.660 -4.461
,
,
HB i j
HB i j
u
uz
Multiplicative effect
,
, ,exp HB i ju
HB i j HB i ju e
Bp Hd <127 127-146 147-166 167+ Pres 0.774 0.786 1.068 1.538 Abs 1.291 1.272 0.936 0.65
, ,ln ijk H i B j C k HB i j HC i ku u u u u u
, ,H i B j C k HB i j HC i ku u u u uuijk e e e e e e
Log-Linear Model
, ,H i B j C k HB i j HC i k
Heart Disease - Cholesterol Interaction
Chol Hd <200 200-219 220-259 260+ Pres -0.233 -0.325 0.063 0.494 Abs 0.233 0.325 -0.063 -0.494
,HC i ku
,
,
HC i k
HC i k
u
uz
Chol Hd <200 200-219 220-259 260+ Pres -1.889 -2.268 0.677 5.558 Abs 1.889 2.268 -0.677 -5.558
Multiplicative effect
,
, ,exp HB i ku
HC i k HB i ku e
Chol Hd <200 200-219 220-259 260+ Pres 0.792 0.723 1.065 1.640 Abs 1.262 1.384 0.939 0.610
Model 2: [BC][BH][CH] Log-linear parameters
Blood pressure-Cholesterol interaction: ,BC j ku
Bp Chol <200 200-219 220-259 260+ <200 0.222 -0.019 -0.034 -0.169 200-219 0.114 -0.041 0.013 -0.086 220-259 -0.114 0.154 -0.058 0.018 260+ -0.221 -0.094 0.079 0.237
,
,
BC j k
BC j k
u
uz
Bp Chol <200 200-219 220-259 260+ <200 2.68 -0.236 -0.326 -1.291 200-219 1.27 -0.472 0.117 -0.626 220-259 -1.502 2.253 -0.636 0.167 260+ -2.487 -1.175 0.785 2.051
Bp Chol <200 200-219 220-259 260+ <200 1.248 0.981 0.967 0.844 200-219 1.120 0.960 1.013 0.918 220-259 0.892 1.166 0.944 1.018 260+ 0.802 0.910 1.082 1.267
Multiplicative effect ,
, ,exp HB j ku
BC j k BC j ku e
Heart disease -Blood Pressure Interaction
Bp Hd <127 127-146 147-166 167+ Pres -0.211 -0.232 0.055 0.389 Abs 0.211 0.232 -0.055 -0.389
,HB i ju
Bp Hd <127 127-146 147-166 167+ Pres -2.125 -2.604 0.542 3.938
Abs 2.125 2.604 -0.542 -3.938
,
,
HB i j
HB i j
u
uz
Multiplicative effect
,
, ,exp HB i ju
HB i j HB i ju e
Bp Hd <127 127-146 147-166 167+ Pres 0.809 0.793 1.056 1.475
Abs 1.235 1.261 0.947 0.678
Heart Disease - Cholesterol Interaction
Chol Hd <200 200-219 220-259 260+ Pres -0.212 -0.316 0.069 0.460
Abs 0.212 0.316 -0.069 -0.460
,HC i ku
,
,
HC i k
HC i k
u
uz
Chol Hd <200 200-219 220-259 260+ Pres -1.712 -2.199 0.732 5.095
Abs 1.712 2.199 -0.732 -5.095
Multiplicative effect
,
, ,exp HB i ku
HC i k HB i ku e
Chol Hd <200 200-219 220-259 260+ Pres 0.809 0.729 1.071 1.584
Abs 1.237 1.372 0.933 0.631
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