Transcript Calculating Effect Sizes for Single Subject Designs

10.0
Systematic Reviews for
Single Subject Designs
Source of Effect Size For SSD
3 Classes Typically Reported
– Standard Mean Difference
– Percentage of Non-Overlapping Data (PND)
– Regression
14
N
U
M
B
E
R
C
O
R
R
E
C
T
12
Baseline
Intervention
(A)
(B)
10
8
6
4
2
0
1
2
3
4
5
6
7
8
9
SESSIONS
10
11
12
13
14
15
Simulation Dataset
Baseline (A) Treatment (B)
1.76
3.64
1.96
3.65
1.50
4.00
2.01
6.51
3.94
7.20
9.70
11.83
2.01
6.51
12.00
X=
sd=
2.12 X=
.74 sd=
6.71
3.52
Sources of Effect Size for SSD
1. Standard Mean Difference
•
•
Subtract the mean of the baseline phase
from the mean of the intervention phase
Divided by standard deviation of baseline
d=
Xtx- Xb
sdb
Sources of Effect Size for SSD
d=
Xtx- Xb
sdb
6.71-2.12
d=
.74
= 6.20
14
N
U
M
B
E
R
C
O
R
R
E
C
T
12
10
8
6
4
2
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
SESSIONS
SMD3= 8.25
SMDall= 7.23
15
14
N
U
M
B
E
R
C
O
R
R
E
C
T
12
10
8
6
4
2
0
1
2
3
4
5
6
7
8
9
10
11
SESSIONS
d = 6.20
12
13
14
15
Interpretation for SMD
• A 6 standard deviation advantage for
the treated participants
• .8 standard deviations=large effect
• The SMD for SSD is not the same
metric as the SMD for group
comparisons
Sources of Effect Size For SSD
2. Percentage of Non-Overlapping Data
(PND)
•
Identify the highest baseline point
•
Count the number of intervention points
that exceed the highest baseline point (nonoverlapping).
•
Calculate the proportion of non-overlapping
to total number of intervention points (can’t
use if baseline has a zero point)
14
N
U
M
B
E
R
C
O
R
R
E
C
T
12
10
8
6
4
2
0
1
2
3
4
5
6
7
8
9
10
11
12
SESSIONS
PND = 7/10 = 70%
13
14
15
Interpretation for PND
PND scale
– 90%+
= Highly Effective
– 70%-90%= Moderately Effective
– 50%-70%= Minimally Effective
– >50%
= Ineffective
Sources of Effect Size SSD
3. Mean Baseline Reduction (MBR)
•
Subtract the average of last 3 Tx points from
the average of the last 3 baseline points
•
Divide by the average of the last 3 baseline
points
•
Multiply by 100 for percent of baseline
reduction (MBR)
Simulation Dataset
Baseline (A) Treatment (B)
1.76
3.64
1.96
3.65
1.50
4.00
2.01
6.51
3.94
7.20
9.70
11.83
2.01
6.51
12.00
X=
1.77
X=
6.84
1.77 - 6.84
MBR =
1.77
x 100 = 286.0
(mean percent reduction)
Interpretation for MBR
• Relative effect: 200% is greater than
100%
• ???? There is no standard for
magnitude of effect.