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_{1-a/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 (DSM-IV).^{30} In addition, a second group including 19 age-matched 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

(±13.0245)

8/7

(±12.47)

9/8

17/16

0.9896

(female/male)

Pretreatment

18.444

22.8235

20.633 (±8.582)

0.2521

BDI

Pretreatment

(±7.384) 11 (±1.581)

(±12.476)

10.454

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