Sample Size Computation
In this study, a group of 33 MDD patients were recruited based on the given formula.^{27,28}
where P is the expected proportion (e.g., expected diagnostic sensitivity); e is the error limit, which is one half the desired width of the confidence interval; and Z_{1a/2} is the standard normal Z value corresponding to a cumulative probability of 1— a/2. The investigator must specify the best guess for the proportion that is expected to be found after performing the study.^{2} The recommended threshold for the statistical parameters used in the computation of the sample size was defined as follows:
 • significance a = 0.05 (alpha)
 • power of test = 80%, в = 0.2 (Beta)
 • expected diagnostic accuracy^{29} P = 90.5%
 • expected error e = 10%
Therefore, for statistical parameters P = 0.905, a = 0.05, e = 0.10, Z_{1— a/2} = 1.96, the sample size is calculated as follows:
Participant Recruitment
In this study, 33 MDD outpatients (16 males and 17 females, mean age = 40.33 ± 12.861) were recruited from the psychiatry clinic at Hospital Universiti Sains Malaysia (HUSM) with signed consent forms. The patients met the internationally recognized diagnostic criteria for depression, as defined in the Diagnostic and Statistical Manual IV (DSMIV).^{30} In addition, a second group including 19 agematched normal controls (8 males and 10 females, mean age = 38.277 ± 15.64) was also recruited. The normal controls were examined medically and were found to be without any psychiatric conditions. The participants from both groups were briefed about the experiment design before its commencement. For MDD patients, after completing 2 weeks of washout time period, the first session of EEG data acquisition was carried out. After the first EEG session, the patients started taking the antidepressants under the general category of SSRIs (see Table 3.1).
Ethics Approval
The experimental design protocol for this study was approved by the Research Ethics Committee of the Hospital Universiti Sains Malaysia (HUSM), Kelantan, Malaysia (FWA Reg. No. 00007718; IRB Reg. No. 00004494). The Subject Information and Consent Form is provided in Appendix 2C.
Table 3.1 Available clinical characteristics of SSRI responders and nonresponders who participated in the study
Information R NR Total p values
Information 
R 
NR 
Total 
p values 
Age (years) 
40.733 
41.176 
40.33 (±12.861) 
0.9224 
Gender 


17/16 
0.9896 
(female/male) Pretreatment 
18.444 
22.8235 
20.633 (±8.582) 
0.2521 
BDI Pretreatment 
(±7.384) 11 (±1.581) 

10.727 (±2.439) 
0.7336 
HADS SSRI treatment^{3} 
E:9,F:2,S:4,Fl:1 
(±3.297) E:4,F:7,S:4,Fl:2 
E:13,F:9,S:8,Fl:3 
Mean (±standard deviation) are shown for the relevant variables
^{a}SSRI medication administered: E, Escitalopram; F, Fluvoxamine; 5, Sertraline; FI, Fluxetine