Kwok_edit_Cardiology_book_temp 08/03/2010 16:05 Page 54
Brain Trauma Stroke
Figure 2: Latent Curve Model for Quality of Life of
depressive symptoms over the seven-year time period. The data
Stroke Patients were collected from 607 MS patients over a seven-year period, with
initial recruitment in 1999 as part of an ongoing longitudinal study
MB11 MB12 MB13 LHS1 LHS2 LHS3 GDS1 GDS2 GDS3
of QoL
16
in chronic illness.
1.0 3.0
1.0 1.0
1.0 3.0
1.0 1.0
1.0 3.0
1.0 1.0 A non-linear trajectory in depression for the sample was suggested
1.0
0.0
1.0
0.0
1.0
0.0
by an examination of randomly selected empirical growth plots. A
Intercept Slope Intercept Slope Intercept Slope
three-factor LCM was used to model the trajectories of depression forξ
1
ξ
2
ξ
3
ξ
4
ξ
5
ξ
6
the MS sample:
y
it
= α
i
+ t
i
β
i
+ t
2
i
γ
i
+ ε
it
(4)
μ
1 Intercept Slope
μ
2
η
1
η
2
1.0 0.0
1.0
1.0 1.0
3.0 where α
i
, β
i
and γ
i
represent the random intercept, slope and
quadratic slope for individual i, respectively. As depicted in Figure 3,
PHY1 PHY2 PHY3
the change pattern and the correlations between the characteristics
of change in depressive symptoms were examined. Furthermore,
Source: Pan et al., 2008.
predictors of change of depression were examined by regressing the
intercept, slope and quadratic slope on the co-variates of interest,
Figure 3: Quadratic Latent Curve Model of
which leads to the following equations:
Depression Across Seven Time-points
α
i
= µ
α
+b
α1
(Age) + b
α2
(TMS) + b
α3
(YMS) + b
α4
(FL) +δ
αi
(5)
β
i
= µ
β
+b
β1
(Age) + b
β2
(TMS) + b
β3
(YMS) + b
β4
(FL) +δ
βi
(6)
Intercept Conditional Quadratic
slope
γ
i
= µ
γ
+b
γ1
(Age) + b
γ2
(TMS) + b
γ3
(YMS) + b
γ4
(FL) +δ
γi
(7)
Findings associated with the aforementioned three specific issues
were obtained.
Time Time Time Time Time Time Time
First, there was no significant increasing or decreasing trend in
1 2 3 4 5 6 7
depressive symptoms, although it fluctuated over time for
E1 E2 E3 E4 E5 E6 E7 individuals. Second, younger age, longer time since diagnosis of MS,
progressive forms of MS and greater extent of FL would result in
Source: Beal et al., 2007.
greater depressive symptoms at time one. Third, FL showed
an association with depression at all time periods, but other
HRQoL of the stroke survivors, while changes in basic functional co-variates did not. In addition, gender did not predict the changes
status and handicap had less significant effects. In this longitudinal in depressive symptoms. These results indicated that screening for
study, LCMs played an important role in delineating the relative depression in all patients with MS was necessary and important.
contribution of basic functional status, handicap and depression in
the HRQoL of stroke patients in a prospective manner. Multilevel Latent Curve Models
In some circumstances, clinical trials involve a multilevel design,
Since the current care services in the sub-acute phase of stroke leading to hierarchically longitudinal data. For example, to evaluate
recovery do not specifically address the problem of post-stroke the effects of a neighbourhood walking programme on QoL among
depression, this study suggests that, apart from drug treatment, there older adults, Fisher and Li
9
used a multilevel sampling scheme to
is a need to devise alternative strategies to manage post-stroke collect a sample of neighbourhoods from a large metropolitan city,
depression for better QoL for stroke survivors. from which older adult residents were randomly recruited. This two-
level design resulted in a nested data structure in which participants
Non-linear Latent Curve Models were clustered within neighbourhoods.
Basic LCMs can be extended to incorporate non-linear trajectories
and effects of co-variates. With this extension, a higher-order The substantive interest of this study focused on whether a six-month
polynomial is used to describe a non-linear pattern of dynamic neighbourhood walking programme would improve neighbourhood-
change in individual characteristics. A longitudinal study about level QoL for senior residents. A two-level LCM of QoL, with individual-
depression in multiple sclerosis (MS)
7
is used for illustration. and neighbourhood-level data structures, is shown in Figure 4. All of
the involved measures were assessed at baseline and at three and six
The study goals focused on three research issues: to reveal the months of the study period.
patterns of change in depressive symptoms over time; to identify
substantial effects of co-variates such as age, type of MS (TMS), Compared with the control neighbourhoods, results from the
years since diagnosis of MS (YMS) and functional limitation (FL) on two-level LCM indicated that physical, mental and satisfaction with
the trajectory of depression over time; and to examine the life aspects of QoL were significantly improved over the course of the
correlations between characteristics of change in FL and six-month intervention. The study concluded that it was feasible and
54 EUROPEAN NEUROLOGICAL REVIEW
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