PsychologicalReports, 1990, 66, 707-714.
@ Psychological Reports 1990
T H E FACTOR STRUCTURE O F T H E MENSTRUAL DISTRESS QUESTIONNAIRE-DUTCH
University of Leiden Summary.-The factor structure of the Dutch adaptation of the Menstrual Distress Questionnaire (MDQ) was studied in a group of 702 women with high probability of premenstrual symptoms. The original factor pattern could not be replicated. Essentially four factors were found: negative affect, concentration, pain, and water retention. This indicates the importance of psychological and somatic symptoms in the premenstrual syndrome.
The premenstrual syndrome has been defined as a condition in which a woman complains of regularly occurring psychological and/or somatic symptoms, that arise in the second half of the menstrual cycle and that are generally relieved with the onset of menstruation, followed by a symptom-free week (O'Brien, et al., 1983). The Menstrual Distress Questionnaire (MDQ) (Moos, 1968) has been a useful instrument in the diagnosis of the premenstrual syndrome (PMS) (Sampson, 1979; Moos, 1985). Six of the original M D Q factors showed variability during the menstrual cycle to be indicative of the syndrome (Clare, 1977). These factors are water retention, pain, autonomic response, negative affect, concentration difficulties, and behavioral change. The first three include mainly somatic symptoms, the others psychological symptoms. On the original questionnaire responses had to be given on six-point scales (ranging from no experience of the symptom to an acute or partially disabling experience of the symptom). But visual analogue scales, lines of exactly 10 cm, provided greater usefulness, quicker completion, greater discrimination and more reliable measurement of changes during the cycle (O'Brien, et al., 1983). Also evaluation of the symptoms had to be given on several days during a menstrual cycle (Clare, 1977; Steiner, et al., 1980; Goudsmit, 1983; O'Brien, et a[., 1983; van der Ploeg, 1989). Although the scaling methods and the wording of the items of Moos' questionnaire have been improved over the past years, the factor pattern remained relatively undiscussed. Moos (1968), without giving much detail, arrived at the structure of the questionnaire by intercorrelation and factor analyses (principal components solution with orthogonal rotation of the factor matrix) of the retrospectively given responses of the total sample (N = 839), separately for menstrual, premenstrual, and intermenstrual phases of the most recent cycle, and for the worst menstrual cycle. The eight result'Address correspondence to Henk M. van der Ploeg, Ph.D., Division of Medical Psychology, University of Leiden, P.O. Box 1251, 2340 BG Oegstgeest, The Netherlands.
708
H.
M.VAN
DER
PLOEG
ing symptom groups were found in essentially all analyses. These eight factors (Moos, 1968) and the numbers of items on which they are based are pain (6), concentration (8), behavioral change (6), autonomic reactions (41, water retention (4), negative affect (8), arousal ( 5 ) , and control (6). The present investigation was designed to study cross-culturally the responses of Dutch women with menstrual problems. They responded to the questionnaire on several days during their menstrual cycle to cross-validate the factor analytic structure of the original Menstrual Distress Questionnaire. It was aimed to report in detail the factor analytic structure of the questionnaire in Dutch, also because description of the factor structure has not been discussed much in the literature. METHOD Newspaper advertisements were used to recruit women who complained of menstrual symptoms. A total of more than 1600 responded. Women who reported the most symptoms before or during menses, not on oral contraceptives, not under treatment for menstrual problems, and not on medications (like Ldopa or sedatives) (N= 1000) were invited to participate in the study. By mail they received four copies of the Dutch adaptation of the Moos' Menstrual Distress Questionnaire (van der Ploeg, 1986). They were asked to answer on each questionnaire in the evening (between 20.00 and 22.00 hr.) of the 12th, 18th, 22nd, and 26th days of the same menstrual cycle (Goudsmit, 1983). Questionnaires had to be returned to the University of Leiden, separately and immediately after responding in addressed and stamped envelopes which were provided. The Dutch version consists of 46 symptoms, indicative of menstrual problems and allow a respondent to evaluate one day ("how did you feel today"). Responses had to be given on visual analogue scales of exactly 10 centimetres, ranging from "not at all" to "very much so." Part of the items are adaptations of the Moos' symptoms, the others are new. In a study of the most significant symptoms indicative of diagnosis of premenstrual syndrome based on the literature and responses of gynaecologists, 10 symptoms were regarded as crucial and an additional 20 of importance. These 30 items are supposed to be the core symptoms used in diagnosis (van der Ploeg, 1989; van der Ploeg & Schwarzer, 1989). Responses on the visual analogue scales are measured in centimetres, so in fact we could analyse "ten-point scales." The responses of 844 women are used (see also van der Ploeg, 1987). They had regular menstrual cycles (26 to 31 days), and they returned the four questionnaires without missing data. Their average age was 33 yr. (SD= 7 yr.), about 60% had one or more children. Thirty-nine percent stated that they had a high level of education, 2lTo reported a low level, and the others in between. In the group of 844 women, 702 indicated before the
MENSTRUAL DISTRESS QUESTIONNAIRE: FACTOR STRUCTURE
709
study that most of their complaints occurred before menstruation or before and during menstruation. The others had most symptoms during menstruation. Because our interest was in the premenstrual syndrome the responses of the 702 women, who may suffer from the syndrome, were factor analysed. Analyses, using SPSS, were performed for each of the four measurement days and for combinations of days.
Daily Variability of Symptoms According to the nature of the premenstrual syndrome, symptoms must vary day to day over the assessments made. The items of the Dutch version of the questionnaire were grouped into four factors, to be described hereafter, each factor consisting of eight symptoms, except water retention which is composed of six. I n Table 1 means and standard deviations are given for each group of symptoms on the four measurement days. Means on Day 22 and Day 26 are clearly higher than those on Day 12 and Day 18. As may be expected, in this group of women with high probability of having the syndrome, the highest scores are on the average obtained on Day 26, just before menstruation. Water retention and negative affect symptoms seem to be most dominant in these subjects. TABLE 1
Day 12 18 22 26
Negative Affect
Concentration
Pain
Water Retention
M
SD
M
SD
M
SD
M
SD
17.9 16.1 19.5 24.0
14.0 11.8 13.5 14.6
14.8 13.5 15.3 18.4
10.7 9.1 11.3 12.7
18.6 17.1 20.1 26.1
11.7 10.3 11.7 13.8
11.4 13.4 16.2 20.3
6.4 8.0 8.9 10.0
Original Moos Factor Pattern
-
The answers on the 36 items composing the six Moos factors and indicative of premenstrual syndrome were factor analysed for the 702 women separately for Days 12, 18, 22, and 26 of their menstrual cycles. Varimax (orthogonal) rotations were performed. The original factor pattern with six factors could not be replicated. O n Day 12 and Day 26 a six-factor solution was psychologically and statistically meaningless. O n Day 18 the six-factor solution could be labeled (in rank order of eigenvalues): negative affect, concentration, water retention, autonomic reactions, pain, and behavioral change. But some items did not load on any factors, and some loaded on two factors. I n addition, the third, fifth, and sixth factors had only a few salient loadings ( 2 . 4 0 ) . O n Day 22 a
710
H. M. VAN
DER
PLOEG
TABLE 2 SALIENT LOADINGSFORFOUR-FACTOR SOLUTIONS BASEDON FACTOR ANALYSESAND VWAX ROTATIONS OF MENSTRUAL DISTRESSQUESTIONNAIRE FOR DUTCHWOMEN WITHA HIGHPROBABILITY OF PMS 1
Day 12 * 2
4
1
Day 18 2 3
4
1
Day 22 2 3
4
Negative Affect crying$ irritability$ mood swings$ depression$ tension$ loneliness$ restlessness$ wordy quarrel Concentration confusion$ avoid social activity lowered judgment$ difficulty concentr.$
decreased efficiency clumsiness$ Pain lowered performance headache$ stay in bed apathy backache2 fatigue$ feeling sick Water Retention weight gain$ painful breasts$ swelling$ sw&ng of feet impulse for activity (30) (36) (36) change eating habits Eigenvalues(umotated) 10.0 1.9 1.6 1.4 10.0 2.1 1.8 1.2 11.8 1.9 1.5 1.4 Note.-N = 702; all loadings 2 . 4 0 are reported; if no salient loadings, in parentheses loadings between .30 and .40 are given; decimal points omitted. $Items loading originally on a Moos factor with the same name.
six-factor solution was also found, but these factor names were concentration plus behavioral change, negative affect, pain, water retention, behavioral change plus autonomic reactions, and negative affect plus autonomic reac-
7 11
MENSTRUAL DISTRESS QUESTIONNAIRE: FACTOR STRUCTURE
TABLE 2 (CONT'D) SALIENTLOADINGS FORFOUR-FACTOR SOLUTIONS BASEDO N FACTOR ANALYSES AND VARIMAX ROTATIONS OF MENSTRUNDISTRESS QUESTIONNAIRE FORDUTCHWOMEN WIW A HIGHPROBABILP~Y OF PMS 2
3
4
1
2
3
Days 12 + 18 + 22 + 26
Days 22 + 26
Days 12 + 18
Day 26 1
4
1
2
3
4
1
2
3
4
I n addition, five-factor solutions were varimax rotated. Again, on Day 12 and Day 26 the resulting patterns could hardly be interpreted, because items loaded on several factors, factors had only one or two salient loadings, and some items did not load on any factors. The patterns on Days 18 and 22 showed these problems as well but had better psychological meaning. Varimax rotations with four factors produced patterns which could be
712
H. M.
VAN DER
PLOEG
interpreted for each of the four days. Essentially the names of the factors are negative affect, concentration, water retention, and pain. The order of the factors, the factor loadings and the detailed composition of the factors varies over the analyses. Instead of grouping the items into the original six factors, a four-factor solution, without the factors of behavioral change and autonomic reactions, produced the psychologically most meaningful factorial interpretation of the menstrual symptoms in these women with high probability of premenstrual syndrome. Factor structure of the Dutch Version2
In expanding the study of the factor structure of the Dutch version of the Menstrual Distress Questionnaire we used the responses of the 702 women, on measurement Days 12, 18, 22, and 26, respectively, and combinations of them, for the 10 crucial and 20 important symptoms indicative of premenstrual pathology (see also van der Ploeg, 1989; van der Ploeg & Schwarzer, 1989). Of these 30 items 25 appeared in the original Moos factors: pain (4), concentration (6), behavioral change (5), water retention (3), and negative affect (7). The other items were not included in the original questionnaire. The factor solutions for each of the days or combination of days were varimax rotated and five factors were extracted. O n none of the days could the original five factors be found, although the items were included. Hardly any of the five-factor solutions met criteria such as, most items have loadings above .40 on one factor, factors have three or more salient loadings, and factors may be interpreted in a psychologically meaningful way. However, four-factor solutions had better psychological meaning and came closer to meeting these criteria. In Table 2 a summary is given of seven factor analyses after varimax rotation. In general four distinct factors could be found: negative affect, concentration, pain, and water retention. The number of items with high loadings on two factors are relatively small (see: confusion and apathy). Items with weak loadings are also found in a limited number (see: cramps, backache, swelling of feet, impulse for activities, change in eating habits). The first factor, in general negative affect, seems to be the most powerful, concentration is the second most important factor, and water retention seems the weakest with a small number of items having salient loadings. The factor solution on Day 26 permitted the easiest interpretation. Combination of Days (12 plus 18, 22 plus 26, all days together) did not give an essentially 'Supporting tables of data, including correlation matrices, are on file in Document NAPS-04763. Remit $7.75 for photocopy or $4.00 for fiche to Microfiche Publications, POB 3513, Grand Central Station, New York, NY 10017.
MENSTRUAL DISTRESS QUESTIONNAIRE: FACTOR STRUCTURE
713
different factor pattern, although the number of items loading on two factors increased.The Dutch version seems to consist of four factors, each factor consisting of eight symptoms, except water retention which is composed of six (see also Table 1). Cronbach alpha reliabilities, as a measure of internal consistency of the factors or symptom groups, are satisfactory or good. The average alpha, based on the measurements on Days 12, 18, 22 and 26, are for negative affect .91, concentration .87, pain .82, and water retention .69. DISCUSSION In this study of Dutch women, who probably suffer from premenstrual syndrome, the original six-factor structure of responses to the questionnaire (Moos, 1968) could not be replicated. However, it is of interest that four of the original factors were replicated: negative affect, concentration, pain and water retention. This four-factor pattern was observed for the original Moos items and also for a smaller number of them together with additional new Dutch items. It should be noted that changing the item composition of the original questionnaire into the adapted Dutch version could have changed the factor structure. Also, the response categories were changed from six-point scales into visual analogue scales. Furthermore, one may suggest that cultural differences in the perception of the menses and menstrual cornplaints could have influenced response patterns. But, psychological and somatic menstrual symptoms can be seen as being of comparable importance in American and in Dutch women. The internal consistency of the four Dutch factors showed that a reliable measurement can be made. These alpha coefficients are more or less alike those reported by Moos (1985), thereby attesting to cross-cultural comparisons. Essential to the concept of premenstrual syndrome is the variability of symptoms. I n the second half of the menstrual cycle, and especially in the week precelng menstruation, a clear increase in symptomatology can be seen. I t became clear that depending upon the day of measurement, for the same group of women a somewhat different factorial structure could be observed. The order of factors may change, the loadings of items on a particular factor changed, and sometimes the number of items belonging to a factor changed. I n general, symptoms on Day 12 and Day 18 were relatively absent, and on Day 26 symptoms were clearly noticeable. The increase in symptom scores, of course, was different for each item and among the women differential responses were also found. Given these sources of variability taken together, it is remarkable that we were able to describe rather consistently four factors for the MDQ-Dutch format as indicative of premenstrual symptomatology. In studying women with high probability of suffering from premenstrual syndrome, one should look for signs and symptoms of a psychological nature (negative affect, difficulties in concentration), and of a somatic nature (pain
714
H . M.
VAN DER
PLOEG
and water retention). These four factors seem to represent the core concepts of the premenstrual syndrome. REFERENCES
CLARE,A. W. (1977) Psychological profiles of women complaining of premenstrual symptoms. Current Medical Research and Opinion, 4(Suppl. 4), 23-28. Psychological aspects of premenstrual symptoms. Journal of Psychosomatic Obstetrics and Gynaecology, 2, 20-26. MOOS, R. H. (1968) The development of a menstrual distress questionnaire. Psychosomatic Medicine, 30, 853-867. Moos, R. H. (1985) Premenstrual symptoms: a manual and overview of research with the Menstrual Distress Questionnaire. Stanford, CA: University School of Medicine. O'BRIEN, P. M. S., FARATIAN, B., GASPAR,A., FILSHIE,G. M., JOHNSON, I. R., & PRESCO-IT, I? (1983) Quantification of premenstrual syndrome: mood assessment, body image, hormones. In R. W. Taylor (Ed.), Premenstrual syndrome. London: Medical News-Tribune. Pp. 7-12. SAMPSON,G. A. (1979) Premenstrual syndrome: a double-blind controlled trial of progesterone and placebo. British Journal of Psychiatry, 135, 209-215. STEINER,M., HASKETT,R. F., & CARROLL, B. J . (1980) Premenstrual tension syndrome: the development of research diagnostic criteria and new rating scales. Acta Psychiatrica Scandinavia, 62, 177-190. VAN DER PLOEG,H . M. (1986) M D Q Menstruatie Khchten Vragenlijst. Lisse: Swets & Zeitlinger. VAN DER PLOEG,H. M. (1987) Emotional states and the premenstrual syndrome. Personality and Individual Diflerences, 8 , 95-100. V A N DER PLOEG,H. M. (1989) Assessment of the Premenstrual Syndrome. International Psychologist, 29(No. 51, 23-30. V A N DER PLOEG,H. M., & SCHWARZER, R. (1989) Emotional changes within the menstrual cycle: anxiety, anger and depression. Journal of Psychosomatic Obstetrics and Gynaecology, 10, 255-267.
GOUDSMIT, E. M. (1983)
Accepted March 18, 1990.
@ Psychological Reports 1990
T H E FACTOR STRUCTURE O F T H E MENSTRUAL DISTRESS QUESTIONNAIRE-DUTCH
University of Leiden Summary.-The factor structure of the Dutch adaptation of the Menstrual Distress Questionnaire (MDQ) was studied in a group of 702 women with high probability of premenstrual symptoms. The original factor pattern could not be replicated. Essentially four factors were found: negative affect, concentration, pain, and water retention. This indicates the importance of psychological and somatic symptoms in the premenstrual syndrome.
The premenstrual syndrome has been defined as a condition in which a woman complains of regularly occurring psychological and/or somatic symptoms, that arise in the second half of the menstrual cycle and that are generally relieved with the onset of menstruation, followed by a symptom-free week (O'Brien, et al., 1983). The Menstrual Distress Questionnaire (MDQ) (Moos, 1968) has been a useful instrument in the diagnosis of the premenstrual syndrome (PMS) (Sampson, 1979; Moos, 1985). Six of the original M D Q factors showed variability during the menstrual cycle to be indicative of the syndrome (Clare, 1977). These factors are water retention, pain, autonomic response, negative affect, concentration difficulties, and behavioral change. The first three include mainly somatic symptoms, the others psychological symptoms. On the original questionnaire responses had to be given on six-point scales (ranging from no experience of the symptom to an acute or partially disabling experience of the symptom). But visual analogue scales, lines of exactly 10 cm, provided greater usefulness, quicker completion, greater discrimination and more reliable measurement of changes during the cycle (O'Brien, et al., 1983). Also evaluation of the symptoms had to be given on several days during a menstrual cycle (Clare, 1977; Steiner, et al., 1980; Goudsmit, 1983; O'Brien, et a[., 1983; van der Ploeg, 1989). Although the scaling methods and the wording of the items of Moos' questionnaire have been improved over the past years, the factor pattern remained relatively undiscussed. Moos (1968), without giving much detail, arrived at the structure of the questionnaire by intercorrelation and factor analyses (principal components solution with orthogonal rotation of the factor matrix) of the retrospectively given responses of the total sample (N = 839), separately for menstrual, premenstrual, and intermenstrual phases of the most recent cycle, and for the worst menstrual cycle. The eight result'Address correspondence to Henk M. van der Ploeg, Ph.D., Division of Medical Psychology, University of Leiden, P.O. Box 1251, 2340 BG Oegstgeest, The Netherlands.
708
H.
M.VAN
DER
PLOEG
ing symptom groups were found in essentially all analyses. These eight factors (Moos, 1968) and the numbers of items on which they are based are pain (6), concentration (8), behavioral change (6), autonomic reactions (41, water retention (4), negative affect (8), arousal ( 5 ) , and control (6). The present investigation was designed to study cross-culturally the responses of Dutch women with menstrual problems. They responded to the questionnaire on several days during their menstrual cycle to cross-validate the factor analytic structure of the original Menstrual Distress Questionnaire. It was aimed to report in detail the factor analytic structure of the questionnaire in Dutch, also because description of the factor structure has not been discussed much in the literature. METHOD Newspaper advertisements were used to recruit women who complained of menstrual symptoms. A total of more than 1600 responded. Women who reported the most symptoms before or during menses, not on oral contraceptives, not under treatment for menstrual problems, and not on medications (like Ldopa or sedatives) (N= 1000) were invited to participate in the study. By mail they received four copies of the Dutch adaptation of the Moos' Menstrual Distress Questionnaire (van der Ploeg, 1986). They were asked to answer on each questionnaire in the evening (between 20.00 and 22.00 hr.) of the 12th, 18th, 22nd, and 26th days of the same menstrual cycle (Goudsmit, 1983). Questionnaires had to be returned to the University of Leiden, separately and immediately after responding in addressed and stamped envelopes which were provided. The Dutch version consists of 46 symptoms, indicative of menstrual problems and allow a respondent to evaluate one day ("how did you feel today"). Responses had to be given on visual analogue scales of exactly 10 centimetres, ranging from "not at all" to "very much so." Part of the items are adaptations of the Moos' symptoms, the others are new. In a study of the most significant symptoms indicative of diagnosis of premenstrual syndrome based on the literature and responses of gynaecologists, 10 symptoms were regarded as crucial and an additional 20 of importance. These 30 items are supposed to be the core symptoms used in diagnosis (van der Ploeg, 1989; van der Ploeg & Schwarzer, 1989). Responses on the visual analogue scales are measured in centimetres, so in fact we could analyse "ten-point scales." The responses of 844 women are used (see also van der Ploeg, 1987). They had regular menstrual cycles (26 to 31 days), and they returned the four questionnaires without missing data. Their average age was 33 yr. (SD= 7 yr.), about 60% had one or more children. Thirty-nine percent stated that they had a high level of education, 2lTo reported a low level, and the others in between. In the group of 844 women, 702 indicated before the
MENSTRUAL DISTRESS QUESTIONNAIRE: FACTOR STRUCTURE
709
study that most of their complaints occurred before menstruation or before and during menstruation. The others had most symptoms during menstruation. Because our interest was in the premenstrual syndrome the responses of the 702 women, who may suffer from the syndrome, were factor analysed. Analyses, using SPSS, were performed for each of the four measurement days and for combinations of days.
Daily Variability of Symptoms According to the nature of the premenstrual syndrome, symptoms must vary day to day over the assessments made. The items of the Dutch version of the questionnaire were grouped into four factors, to be described hereafter, each factor consisting of eight symptoms, except water retention which is composed of six. I n Table 1 means and standard deviations are given for each group of symptoms on the four measurement days. Means on Day 22 and Day 26 are clearly higher than those on Day 12 and Day 18. As may be expected, in this group of women with high probability of having the syndrome, the highest scores are on the average obtained on Day 26, just before menstruation. Water retention and negative affect symptoms seem to be most dominant in these subjects. TABLE 1
Day 12 18 22 26
Negative Affect
Concentration
Pain
Water Retention
M
SD
M
SD
M
SD
M
SD
17.9 16.1 19.5 24.0
14.0 11.8 13.5 14.6
14.8 13.5 15.3 18.4
10.7 9.1 11.3 12.7
18.6 17.1 20.1 26.1
11.7 10.3 11.7 13.8
11.4 13.4 16.2 20.3
6.4 8.0 8.9 10.0
Original Moos Factor Pattern
-
The answers on the 36 items composing the six Moos factors and indicative of premenstrual syndrome were factor analysed for the 702 women separately for Days 12, 18, 22, and 26 of their menstrual cycles. Varimax (orthogonal) rotations were performed. The original factor pattern with six factors could not be replicated. O n Day 12 and Day 26 a six-factor solution was psychologically and statistically meaningless. O n Day 18 the six-factor solution could be labeled (in rank order of eigenvalues): negative affect, concentration, water retention, autonomic reactions, pain, and behavioral change. But some items did not load on any factors, and some loaded on two factors. I n addition, the third, fifth, and sixth factors had only a few salient loadings ( 2 . 4 0 ) . O n Day 22 a
710
H. M. VAN
DER
PLOEG
TABLE 2 SALIENT LOADINGSFORFOUR-FACTOR SOLUTIONS BASEDON FACTOR ANALYSESAND VWAX ROTATIONS OF MENSTRUAL DISTRESSQUESTIONNAIRE FOR DUTCHWOMEN WITHA HIGHPROBABILITY OF PMS 1
Day 12 * 2
4
1
Day 18 2 3
4
1
Day 22 2 3
4
Negative Affect crying$ irritability$ mood swings$ depression$ tension$ loneliness$ restlessness$ wordy quarrel Concentration confusion$ avoid social activity lowered judgment$ difficulty concentr.$
decreased efficiency clumsiness$ Pain lowered performance headache$ stay in bed apathy backache2 fatigue$ feeling sick Water Retention weight gain$ painful breasts$ swelling$ sw&ng of feet impulse for activity (30) (36) (36) change eating habits Eigenvalues(umotated) 10.0 1.9 1.6 1.4 10.0 2.1 1.8 1.2 11.8 1.9 1.5 1.4 Note.-N = 702; all loadings 2 . 4 0 are reported; if no salient loadings, in parentheses loadings between .30 and .40 are given; decimal points omitted. $Items loading originally on a Moos factor with the same name.
six-factor solution was also found, but these factor names were concentration plus behavioral change, negative affect, pain, water retention, behavioral change plus autonomic reactions, and negative affect plus autonomic reac-
7 11
MENSTRUAL DISTRESS QUESTIONNAIRE: FACTOR STRUCTURE
TABLE 2 (CONT'D) SALIENTLOADINGS FORFOUR-FACTOR SOLUTIONS BASEDO N FACTOR ANALYSES AND VARIMAX ROTATIONS OF MENSTRUNDISTRESS QUESTIONNAIRE FORDUTCHWOMEN WIW A HIGHPROBABILP~Y OF PMS 2
3
4
1
2
3
Days 12 + 18 + 22 + 26
Days 22 + 26
Days 12 + 18
Day 26 1
4
1
2
3
4
1
2
3
4
I n addition, five-factor solutions were varimax rotated. Again, on Day 12 and Day 26 the resulting patterns could hardly be interpreted, because items loaded on several factors, factors had only one or two salient loadings, and some items did not load on any factors. The patterns on Days 18 and 22 showed these problems as well but had better psychological meaning. Varimax rotations with four factors produced patterns which could be
712
H. M.
VAN DER
PLOEG
interpreted for each of the four days. Essentially the names of the factors are negative affect, concentration, water retention, and pain. The order of the factors, the factor loadings and the detailed composition of the factors varies over the analyses. Instead of grouping the items into the original six factors, a four-factor solution, without the factors of behavioral change and autonomic reactions, produced the psychologically most meaningful factorial interpretation of the menstrual symptoms in these women with high probability of premenstrual syndrome. Factor structure of the Dutch Version2
In expanding the study of the factor structure of the Dutch version of the Menstrual Distress Questionnaire we used the responses of the 702 women, on measurement Days 12, 18, 22, and 26, respectively, and combinations of them, for the 10 crucial and 20 important symptoms indicative of premenstrual pathology (see also van der Ploeg, 1989; van der Ploeg & Schwarzer, 1989). Of these 30 items 25 appeared in the original Moos factors: pain (4), concentration (6), behavioral change (5), water retention (3), and negative affect (7). The other items were not included in the original questionnaire. The factor solutions for each of the days or combination of days were varimax rotated and five factors were extracted. O n none of the days could the original five factors be found, although the items were included. Hardly any of the five-factor solutions met criteria such as, most items have loadings above .40 on one factor, factors have three or more salient loadings, and factors may be interpreted in a psychologically meaningful way. However, four-factor solutions had better psychological meaning and came closer to meeting these criteria. In Table 2 a summary is given of seven factor analyses after varimax rotation. In general four distinct factors could be found: negative affect, concentration, pain, and water retention. The number of items with high loadings on two factors are relatively small (see: confusion and apathy). Items with weak loadings are also found in a limited number (see: cramps, backache, swelling of feet, impulse for activities, change in eating habits). The first factor, in general negative affect, seems to be the most powerful, concentration is the second most important factor, and water retention seems the weakest with a small number of items having salient loadings. The factor solution on Day 26 permitted the easiest interpretation. Combination of Days (12 plus 18, 22 plus 26, all days together) did not give an essentially 'Supporting tables of data, including correlation matrices, are on file in Document NAPS-04763. Remit $7.75 for photocopy or $4.00 for fiche to Microfiche Publications, POB 3513, Grand Central Station, New York, NY 10017.
MENSTRUAL DISTRESS QUESTIONNAIRE: FACTOR STRUCTURE
713
different factor pattern, although the number of items loading on two factors increased.The Dutch version seems to consist of four factors, each factor consisting of eight symptoms, except water retention which is composed of six (see also Table 1). Cronbach alpha reliabilities, as a measure of internal consistency of the factors or symptom groups, are satisfactory or good. The average alpha, based on the measurements on Days 12, 18, 22 and 26, are for negative affect .91, concentration .87, pain .82, and water retention .69. DISCUSSION In this study of Dutch women, who probably suffer from premenstrual syndrome, the original six-factor structure of responses to the questionnaire (Moos, 1968) could not be replicated. However, it is of interest that four of the original factors were replicated: negative affect, concentration, pain and water retention. This four-factor pattern was observed for the original Moos items and also for a smaller number of them together with additional new Dutch items. It should be noted that changing the item composition of the original questionnaire into the adapted Dutch version could have changed the factor structure. Also, the response categories were changed from six-point scales into visual analogue scales. Furthermore, one may suggest that cultural differences in the perception of the menses and menstrual cornplaints could have influenced response patterns. But, psychological and somatic menstrual symptoms can be seen as being of comparable importance in American and in Dutch women. The internal consistency of the four Dutch factors showed that a reliable measurement can be made. These alpha coefficients are more or less alike those reported by Moos (1985), thereby attesting to cross-cultural comparisons. Essential to the concept of premenstrual syndrome is the variability of symptoms. I n the second half of the menstrual cycle, and especially in the week precelng menstruation, a clear increase in symptomatology can be seen. I t became clear that depending upon the day of measurement, for the same group of women a somewhat different factorial structure could be observed. The order of factors may change, the loadings of items on a particular factor changed, and sometimes the number of items belonging to a factor changed. I n general, symptoms on Day 12 and Day 18 were relatively absent, and on Day 26 symptoms were clearly noticeable. The increase in symptom scores, of course, was different for each item and among the women differential responses were also found. Given these sources of variability taken together, it is remarkable that we were able to describe rather consistently four factors for the MDQ-Dutch format as indicative of premenstrual symptomatology. In studying women with high probability of suffering from premenstrual syndrome, one should look for signs and symptoms of a psychological nature (negative affect, difficulties in concentration), and of a somatic nature (pain
714
H . M.
VAN DER
PLOEG
and water retention). These four factors seem to represent the core concepts of the premenstrual syndrome. REFERENCES
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GOUDSMIT, E. M. (1983)
Accepted March 18, 1990.
