.Wefoundthatthemodelcontainingthefactorsanxiety,gloominessandsomatic/vege-tativewasonaveragethebestpredictingandthemostcorrectmodel. (IDS-C ),threetimesinahalfyearperiod.DuringthisperiodthesubjectsreceivedCognitiveBehaviouralTherapy.Tofindtheunderlyingfact

The underlying factors of depression

A factor analysis on the items of the IDS-C 30

Bachelor thesis in Mathematics

January 2015

Student: Leslie Zwerwer, s2183846

Primary supervisor: prof. dr. E.C. Wit

Secondary supervisor: dr. W.P. Krijnen

Abstract

In this research we investigated the underlying factors of depression. The sample contained 2981 subjects with the following characteristics: "healthy", suffering from Major Depressive Disorder or suffering from Bipolar II Disorder. They completed the Inventory of Depressive Symptomatology-Clinican 30 (IDS-C 30 ), three times in a half year period. During this period the subjects received Cognitive Behavioural Therapy.

To find the underlying factors we used different methods. First we generated three

models using exploratory factor analysis. Subsequently we tested these models using

confirmatory factor analysis. We also tested a model that was suggested by the IDS-C ₃₀ .

We found that the model containing the factors anxiety, gloominess and somatic/vege-

tative was on average the best predicting and the most correct model.

Contents

Introduction 4

Methods 5

Inventory of Depressive Symptomatology-Clinican 30 . . . . 5

Initial data analysis . . . . 6

Exploratory factor analysis . . . . 12

Interpretation . . . . 15

Estimating scores on factors or variables . . . . 17

Confirmatory factor analysis . . . . 18

Goodness of fit indices . . . . 21

Confirmatory factor analysis with ordinal data . . . . 23

Measurement invariance . . . . 26

Missing values . . . . 27

Results 28 Results exploratory factor analysis . . . . 28

Results confirmatory factor analysis . . . . 30

Results confirmatory factor analysis with ordered variables . . . . 31

Results measurement invariance . . . . 32

Results multiple imputation . . . . 34

Discussion 35 Discussion exploratory factor analysis . . . . 35

Discussion confirmatory factor analysis . . . . 37

Discussion measurement invariance . . . . 39

Discussion multiple imputation . . . . 39

Some suggestions for further research . . . . 39

References 41 Appendices 43 Appendix A . . . . 43

Appendix B . . . . 43

Appendix C . . . . 47

Introduction

Almost everyone has dealt with depression in some way. It is the most common psy- chological illness in the world. According to the World Health Organization (www.who.int), globally more than 350 million people are suffering from depression. Moreover it is the most common cause of disability in the world and a major contributor to the global burden of diseases. Depression is a rich concept and there are a lot of unanswered questions about this psychological illness. For example: why are some people more sensitive to develop a depression than others? And why does the length of a depres- sion differ among people? Therefore it is important to research the different symptoms and causes of depression. There are different kinds of depression. The three most important kinds are: Major Depressive Disorder (MDD), Dysthemic Disorder (DD) and Bipolar Disorder (BD). In this article we focus on the Major Depressive Disorder and Bipolar II Disorder. According to the DSM-IV (American Psychiatric Association, 1994, pp.327), "someone is suffering from Major Depressive Disorder if he is experiencing five (or more) of the following symptoms. These symptoms have to be present during the same 2-week period and they represent a change from previous functioning. More- over at least one of the symptoms is either (1) depressed mood or (2) loss of interest or pleasure. Note: symptoms that are clearly due to a general medical condition or mood-incongruent delusions or hallucinations are excluded.

1. depressed mood most of the day, nearly every day.

2. markedly diminished interest or pleasure in all, or almost all, activities most of the day, nearly every day.

3. significant weight loss when not dieting or weight gain (e.g., a change of more than 5% of body weight in a month), or decrease or increase in appetite nearly every day.

4. insomnia or hypersomnia nearly every day.

5. psychomotor agitation or retardation nearly every day.

6. fatigue or loss of energy nearly every day.

7. feelings of worthlessness or excessive or inappropriate guilt (which may be delusional) nearly every day.

8. diminished ability to think or concentrate, or indecisiveness, nearly every day.

9. recurrent thoughts of death (not just fear of dying), recurrent suicidal ideation without a specific plan, or a suicide attempt or a specific plan for committing suicide.

Moreover the symptoms should not meet criteria for a Mixed Episode. The symp-

toms cause clinically significant distress or impairment in social, occupational, or other

important areas of functioning. Furthermore the symptoms are not due to the direct

physiological effects of a substance (e.g., a drug of abuse, a medication) or a general

medical condition (e.g., hypothyroidism). Last, the symptoms are not better accounted

for by bereavement, i.e., after the loss of a loved one, the symptoms persist for longer

than 2 months or are characterized by marked functional impairment, morbid preoc- cupation with worthlessness, suicidal ideation, psychotic symptoms, or psychomotor retardation."

Bipolar II Disorder differs in some ways from Major Depressive Disorder. According to the DSM-IV (American Psychiatric Association, 1994, pp. 362), ”someone is suffering from Bipolar II Disorder if he is experiencing all of the following symptoms:

1. Presence (or history) of one or more Major Depressive Episodes.

2. Presence (or history) of at least one Hypomanic Episode.

3. There has never been a Manic Episode or a Mixed Episode.

4. The mood symptoms in Criteria (1) and (2) are not better accounted for by Schizoaffective Disorder and are not superimposed on Schizophre- nia, Schizophreniform Disorder, Delusional Disorder, or Psychotic Dis- order Not Otherwise Specified.

5. The symptoms cause clinically significant distress or impairment in social, occupational, or other important areas of functioning.”

A Hypomanic Episode is defined as a distinct period during which there is an ab- normally and persistently elevated, expansive, or irritable mood that lasts at least four days. Moreover a manic episode is defined by a distinct period during which there is an abnormally and persistently elevated, expansive, or irritable mood. This period of abnormal mood must last at least one week. Furthermore a Mixed Episode is charac- terized by a period of time (lasting at least 1 week) in which the criteria are met both for a Manic Episode and for a Major Depressive Episode nearly every day.

In this article we will start discussing the initial data analysis. Moreover we will ex- plain exploratory factor analysis and confirmatory factor analysis for continuous vari- ables. We will continue with a subsection about goodness of fit indices and a subsection about confirmatory factor analysis for ordinal variables. Subsequently we will explain the concepts of measurement invariance and multiple imputation. After that the results of the different analyses are shown. In the last section we will discuss these results.

Methods

Inventory of Depressive Symptomatology-Clinican ₃₀

In this research we used data from Nesda ("Nederlandse Study naar Depressie en Angst", translates as "The Dutch Study of Depression and Anxiety") (Boschloo et al., 2014). The Inventory of Depressive Symptomatology-Clinican ₃₀ (IDS-C ₃₀ ) was filled in by 2981 subjects. There were three kinds of subjects participating in this research:

subjects suffering from major depression, subjects suffering from bipolar II disorder

and subjects who did not suffer from depression. It would be interesting to look at the

differences in the factor structure between these three groups, however this falls out-

side the scope of the thesis. At three different moments subject were asked to fill in the

IDS-C ₃₀ . The first moment was at the starting point of the cognitive behavioural ther- apy, the second and the third moment were respectively three months and six months later.

The IDS-C 30 contains 30 items about criterion symptoms of depression, commonly associated symptoms and items relevant to melancholic or atypical symptom features.

All DSM-IV criterion items for major depressive episodes are included in the test. There is evidence of the psychometric properties of the IDS-C 30 for depressed inpatients (Corruble, Legrand, Duret, Charles & Guelfi, 1999) as well as depressed outpatients (Trivedi et. al., 2004). Moreover it can be used to evaluate depressive symptom sever- ity (Rush, Gullion, Basco, Jarrett & Trivedi, 1996). Furthermore factor analysis on the IDS, Hamilton Depression Rating Scale (HDRS) and Beck Depression Inventory (BDI) has revealed that the IDS provided more complete factor coverage than the HDRS or BDI did (Gullion & Rush, 1998).

There are four options for every item in the IDS-C ₃₀ . Each item can be rated from 0 to 3 , where 0 is indicating no suffering and 3 is indicating extreme suffering from this symptom. The IDS-C 30 was not completed by all subjects at all three measurements.

Some subjects participated just in one or two measurements.

One can find the IDS-C 30 in Appendix B. To complete the IDS-C 30 one needs to answer 28 items, because items 11 and 12 , and items 13 and 14 are each other opposites.

Therefore one needs to complete either item 11 or 12 and either item 13 or 14 . We will refer to items 11 or 12 as item 11 and to items 13 or 14 as item 12 . Moreover we will refer to items number 15 − 30 as respectively items 13 − 28 .

Items number 1 − 4 were concerned with sleep. Items number 5 − 10 were con- cerned with mood. Items number 12 , 18 − 26 and 28 were concerned with evaluating somatic symptoms. The symptoms concerning appetite were measured with item 11 . The mental symptoms of depression were measured with items 13 − 17 and item 27 . Initial data analysis

The frequencies of the answers to the different questions are shown in figure 1, figure 2 and figure 3. It is easy to see that the most common answer was 0 . So the majority of the subjects did not experience any suffering from the symptoms. The most rare answer was option 3 , indicating that most subjects did not experience severe suffering from the symptoms.

We now look more precisely at figure 1. We will refer to the first, second and third measurement moment, using respectively T1, T2 and T3. Item number 9 was the most unanswered item. This could be due to comprehensibility of the question or the item was too confronting for some subjects. Also items number 3 , 8 and 20 were more often unanswered than other items. Item number 28 was filled in by every subject who participated at T1. Furthermore item number 14 shows a different pattern with respect to the other items. When we look at the frequency of answers in item 14 , one can see that far more people answered option 3 than 2 . At T1 there were 2947 participants and 2640 participants answered all items (i.e. there were 307 subjects with missing values).

The frequencies of the answers to the different questions with respect to T2 are

shown in figure 2. In accordance with the first measurement item number 9 was the most unanswered item. Also items number 3 , 8 and 20 were more often unanswered than other items. Items number 1 and 5 were most frequently filled in. Notice that item 14 has the same pattern as at T1. At T2 there were 2444 participants and 2108 subjects answered all items (i.e. there were 336 subjects with missing values).

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28

3 2 1 0 First measurement

Items (1−28)

0 500 1000 1500 2000 2500 3000

Figure 1. : Frequencies of the answers at the first measurement moment (T1)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28

3 2 1 0 Second measurement

Items (1−28)

0 500 1000 1500 2000 2500 3000

Figure 2. : Frequencies of the answers at the second measurement moment (T2)

The frequencies of the answers to the different questions with respect to T3 are

shown in figure 3. In accordance with T1 and T2 item number 9 was the most unan-

swered item. Also item number 8 was more often unanswered than other items. Item

number 6 was completed by almost every subject participating at T3; just one partici- pant did not answer this item. Notice that item 14 has the same pattern in T1, T2 and T3. In T3 there were 2505 participants and 2312 participants answered all items (i.e.

there were 193 subjects with missing values).

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28

3 2 1 0 Third measurement

Items (1−28)

0 500 1000 1500 2000 2500 3000

Figure 3. : Frequencies of the answers at the third measurement moment (T3)

Now we added the answers of the items concerning sleep, mood, somatic, appetite and mental for every subject. We did this for all three measurement moments. We want to find correlations between these sum variables. We make use of Spearman’s rank order, because all variables are ordinal. Spearman’s rank order is a nonparamet- ric technique. This means that it is not affected by the distribution of the population (Gauthier, 2001). The spearman rank order coefficient ranges from −1 to 1 . The for- mula for spearman rank order is the following:

r _s =

n ³ −3 6 − P _n

i=1 d ² _i − P T _x − P T _y r h

n ³ −3

6 − 2 P T _x i h

n ³ −3

6 − P T _y i

where n is the number of data pairs and d i is the difference between the rank of x i

and y i . Moreover P T _x and P T _y are defined in the following way:

X T x =

n

X

j=1

t ³ _j − t _j

12 ⁽¹⁾

X T _y =

n

X

j=1

t ³ _j − t _j

12 ⁽²⁾

where t _j is the numbers of ties in group j . Moreover equation 1 is for the x values and equation 2 is for the y values. Subsequently we calculated Spearman’s rank order for the sum variables. We only used the complete cases. The results are presented in table 1, 2 and 3.

Table 1: Spearman’s rank order for the first measurement moment (T1) Appetite Mental Mood Sleep Somatic Appetite 1.000 0.492 0.463 0.278 0.539

Mental 0.492 1.000 0.795 0.410 0.772

Mood 0.463 0.795 1.000 0.425 0.765

Sleep 0.278 0.410 0.425 1.000 0.472

Somatic 0.539 0.772 0.765 0.472 1.000

Table 2: Spearman’s rank order for the second measurement moment (T2) Appetite Mental Mood Sleep Somatic Appetite 1.000 0.409 0.383 0.227 0.470

Mental 0.409 1.000 0.748 0.352 0.714

Mood 0.383 0.748 1.000 0.324 0.695

Sleep 0.227 0.352 0.324 1.000 0.431

Somatic 0.470 0.714 0.695 0.431 1.000

Table 3: Spearman’s rank order for the third measurement moment (T3) Appetite Mental Mood Sleep Somatic Appetite 1.000 0.400 0.384 0.216 0.468

Mental 0.400 1.000 0.751 0.383 0.712

Mood 0.384 0.751 1.000 0.362 0.693

Sleep 0.216 0.383 0.362 1.000 0.426

Somatic 0.468 0.712 0.693 0.426 1.000

All sum variables have positive correlation between each other. We define a corre- lation of bigger than 0.70 as very large (cf. Hemphill, 2003). Therefore the following sum variables seem to be highly correlated ( |r| > 0.70 ) at T1: ”Somatic and Mental”,

”Mood and Mental” and ”Somatic and Mood”. At T2 and T3 the correlations of ”Somatic

and Mental” and ”Mood and Mental" are very large. At all measurement moments the

correlation of "Sleep and Appetite" seem to have a low correlation ( |r| < 0.30 ). One

interesting thing is that all correlations of T2 and T3 are lower than the correlations of

T1. It is possible that the dropouts had equality in terms of their rank score. If so the

correlations will be lower at T2 and T3.