Early work by Wegner et al. (
1987) and Wegner (
1992,
1994) showed that attempts to suppress thoughts may have the paradoxical effect of increasing the number of intrusive thoughts one is having (rebound effect). This increase in intrusive thoughts may persist after suppression is no longer actively pursued and is even thought to cause undesirable outcomes such as obsessions (Lane and Wegner
1995). Although this ironic consequence of unsuccessful thought suppression has repeatedly been documented in experimental settings using predominantly neutral stimuli (such as the infamous white bear), empirical support for a ubiquitous negative role of suppression and its rebound effect in the persistence of thoughts has been mixed. For example, several factors have been identified that may limit the generalizability of suppression research such as whether the material to be suppressed is positive, negative, or neutral and self-relevant (Salkovkis and Campbell
1994). In addition, unsuccessful suppression of obsessive thoughts in particular may lead to an increase in intrusive thoughts, and unsuccessful suppression of neutral or positive thoughts are considerably less affected by Wegner’s (
1994) thought suppression paradox (Purdon and Clark
2001). Finally, successful thought suppression has also been documented (e.g., Brewin and Beaton
2002), in particular when one has positive beliefs about having control over one’s thoughts (Wenzlaff and Wegner
2000). Given this unresolved debate on whether thought suppression is a successful or unsuccessful mechanism of thought control, it is important that instruments that aim to assess thought suppression distinguish successful from unsuccessful thought suppression in order to better understand the dynamics of thought suppression as thought control mechanism.
Wegner and Zanakos (
1994) developed a unidimensional thought suppression measure to identify individuals that use thought suppression as the default thought control strategy and are therefore more susceptible to experience intrusive thoughts. This measure, the White Bear Suppression Inventory (WBSI), is since its development the most widely used instrument to assess thought suppression. However, several authors suggest the WBSI also measures the experience of intrusive thoughts (e.g., Höping and De Jong-Meyer
2003). Rassin (
2003) points out the importance to distinguish thought suppression and thought intrusion as the frequency of thought intrusions that one experiences may not only be the result of unsuccessful thought suppression but also the
cause for thought suppression in the first place. In other words, it is unclear how to interpret a high WBSI score: as a measure of thought suppression or of the number of intrusive thoughts.
To address these limitations of the WBSI, Rassin (
2003) developed the Thought Suppression Inventory (TSI) to assess thought suppression attempts as well as thought intrusion and successful thought suppression. The TSI is a brief self-report measure that consists of 15 items that contribute to three 5-item subscales measuring thought intrusion (Int), thought suppression (Sup) and successful (effective) thought suppression (in this study abbreviated as “Eff” to better distinguish from Sup). Table
1 (first column) shows the items and how they are distributed among the three scales. In addition to its dimensionality, Rassin also reported satisfactory test-retest reliability for Int and Eff (a lower than desired test-retest reliability was found for Sup, given its supposed trait-like character) and external validity in two student samples. Given the earlier mentioned importance to adequately disentangle Int, Sup, and Eff, the aim of this study is to investigate the factorial structure of the TSI using PAF, CFA and the less well-known but more sophisticated Mokken scale analysis (MSA). To avoid on one side the significantly distorted frequency distribution and skew often present in data sampled from a clinical population and the low generalizability to clinical populations of student data on the other side, a senior citizen sample was used for this study. Epidemiological studies show that community-dwelling elderly experience substantial rates of relatively common mental disorders related to the occurrence of intrusive thoughts such as depression, obsessive-compulsive disorder, and generalized anxiety disorder (Kessler et al.
2005). Hence, where the occurrence of thought intrusion is concerned, senior citizen data (in comparison with student data) may be more representative for a clinical population, without being subject to significantly distorted answering tendencies that are indicative of a clinical population.
Table 1
Item content, pattern coefficients of the 2-factor model and the 3-factor model after oblimin rotation using principal axis factoring, and results of the automated item selection procedure in exploratory factor analysis
1.I have many unpleasant thoughts (I) | .76 | -.08 | .72 | -.14 | -.02 | .38 | | .46 | | | .52 | | | .55 | | |
4. I experience many emotions that are too intense to control (I) | .55 | -.13 | .54 | -.12 | .06 | .27 | | .33 | | | us | us | us | us | us | us |
7.I have thoughts which I would rather not have(I) | .75 | .06 | .75 | -.01 | -.05 | .43 | | .50 | | | .54 | | | .56 | | |
10.I regularly ‘hear’ unexplainable things inside my head, such as my own voice, or the voices of people who are not present(I) | .39 | -.08 | .44 | .01 | .12 | .25 | | .32 | | | us | us | us | us | us | us |
13.I am unable to concentrate(I) | .53 | -.01 | .45 | -.15 | -.13 | .30 | | .34 | | | .41 | | | us | us | us |
2.I always try to forget unpleasant events as fast as possible(S) | .27 | .54 | .08 | .06 | -.63 | .25 | | | .41 | | | .53 | | | .57 | |
5.I always try to put problems out of mind(S) | .14 | .57 | -.13 | .01 | -.77 | | .25 | | .45 | | | .49 | | | .57 | |
8.If I have an unpleasant thought, I try to think about something else(S) | .33 | .59 | .34 | .36 | -.31 | .32 | | .29 | | | | .44 | | us | us | us |
11.Sometimes I stay busy just to prevent having certain thoughts(S) | .64 | .25 | .70 | .18 | -.08 | .41 | | .45 | | | .49 | | | .53 | | |
14.I try to avoid certain thoughts(S) | .62 | .36 | .47 | -.02 | -.44 | .42 | | .43 | | | .47 | | | .50 | | |
3.I am able to keep a problem out of mind until I have time to deal with it(E) | -.27 | .50 | .01 | .72 | .14 | | .36 | | | .45 | | | .51 | | | .57 |
6.I am able to suppress unpleasant thoughts(E) | -.24 | .75 | -.07 | .69 | -.17 | | .46 | | .37 | | | | .53 | | | .57 |
9.I am able to put aside problems and worries(E) | -.43 | .50 | -.23 | .59 | .02 | | .36 | | | .45 | | | .47 | us | us | us |
12-I am able to suppress unpleasant experiences to the point that I hardly remember them(E) | .11 | .46 | .12 | .29 | -.25 | .16 | | | .35 | | us | us | us | us | us | us |
15.I can keep the lid on my feelings if letting them out would interfere with what I am doing(E) | -.12 | .39 | -.04 | .35 | -.10 | | .28 | us | us | us | us | us | us | us | us | us |
Scale H | | | | | .32 | .34 | .39 | .40 | .45 | .40 | .49 | .50 | .54 | .57 | .57 | |
Discussion
The aim of this study was to examine the dimensionality of the Thought Suppression Inventory, developed by Rassin (
2003). Opposed to EFA (PAF, but MAP and PA in particular), it was suggested by exploratory and confirmatory MSA and CFA that the original 3-factor model as proposed by Rassin is to be preferred. These three factors are Intrusion, Suppression and Successful Suppression.
Although the three-dimensional structure is suggested, the analysis showed that several items turned out to have unsatisfactory psychometric properties. First, the pattern matrix following Oblimin rotation showed that item 14Sup had almost similar loadings on Int and Sup and that item 8Sup had almost similar loadings on all three scales. In addition, item 12Eff also loaded on all three factors with minimum differences between factorloadings of .10 and .13, insufficient to clearly discriminate between the factors. Second, exploratory and confirmatory MSA suggested that item 15Eff was unscalable even at the smallest lowerbound c. In addition, it suggested that Int consisted of a strong core around items 1, 4 and 7, that Sup consisted of a strong core of items 8, 11, and 14 and, finally, that Eff had a strong core of items 3, 6, and 9. This suggests that the weaker items 2, 5, 10, and 13 should at least be rephrased or even removed. Finally, Items 12 and 15 had H < .3 which indicates the items are unscalable. CFA showed that item 8Sup loaded on both Sup and Eff. Hence, from 15 items, 8 items were marked as unsound and should either be rephrased or removed.
It is important to consider whether low scalability means that the item is a weak indicator of the latent trait one aims to measure or that it is the result of poor wording of the items (Emons et al.
2010). Indeed, several items of the TSI might improve by rewording the items. For example, the wording of item 10Int,
“I regularly ‘hear’ unexplainable things inside my head, such as my own voice, or the voices of people who are not present” may be too strong and disturbing (also evidenced by the lowest item mean of all TSI items) and in addition may assess the experience of intrusive perceptions rather than intrusive thoughts. Rewording the item by, for example, using a more daily life example of having intrusive thoughts (such as not being able to put the errands one must run that day out of mind), may benefit its scalability.
MSA provided a detailed analysis of the items’ scalability and the dimensional structure of the TSI. By progressively increasing the lower bound
c for scalability and thus placing stronger demands on the data structure, MSA provided alternating ways of forming scales. Studying this pattern of alternating cluster outcomes provides detailed information on the most appropriate conclusion with respect to scalability and dimensionality (Wismeijer et al.
2008). Various small differences between men and women with respect to how items were clustered were detected. However, in both genders the same conclusion was reached that a three-dimensional structure best fitted the TSI data, and that these three dimensions consisted of the same content. This is an asset that brings additional validity to the main finding of this study that the TSI indeed can be best regarded as a three-dimensional instrument.
The finding that the Suppression and Successful Suppression factors should be distinguished and can best be treated as two separate dimensions corroborates the literature that found that both may have separate dynamics and consequences for the number of subsequent thought intrusions (Blumberg
2000; Höping and de Jong-Meyer
2003; Muris et al.
1996; Rassin
2003). The controversy on whether unsuccessful thought suppression indeed leads to a rebound effect partially focuses on the potential determinants of the rebound effect such as unfocused distraction (Wegner et al.
1991), asymmetry of associate priming in suppression (Najmi and Wegner
2009), metacognitive beliefs about thought processes (Clark and Purdon
1993,
1995) and different types of intrusive thoughts such as neutral, positive or negative thoughts (Salkovkis and Campbell
1994), ego-dystonic thoughts and so forth. However, few studies have explicitly investigated both successful and unsuccessful suppression simultaneously and most research on thought suppression used the WBSI that implicitly assessed unsuccessful thought suppression instead of thought suppression (Rassin
2003). Including a measure of successful suppression in future investigations is desirable to better understand under what circumstances and why successful suppression is indeed possible and when it leads to the rebound effect.
In light of the above discussion it is relevant to note that the Suppression factor may benefit from being renamed. First, it is rather odd that Effective Suppression, which one intuitively would assume is subsumed under the broader label ‘Suppression’, contains entirely different items and hence measures something else than Suppression. Second, scrutiny of the Suppression items suggests that the items do not assess thought suppression per se, but rather one’s intention or efforts to suppress one’s thoughts. This is caused by the words ‘try to’ (e.g. “I try to avoid certain thoughts”) that is present in 4 of the 5 Suppression items. Renaming the Suppression factor into, for example, ‘Thought Suppression Efforts’ or ‘Intention to Suppress Thoughts’ may solve this somewhat confusing situation.
Most noticeably, clinical populations such as OCD patients may benefit from a nuanced understanding of the relation between thought suppression techniques and intrusive thoughts as the current debate and inconsistent findings on what causes the rebound effect may inadvertently downplay the importance of the thought suppression paradox in the maintenance of obsessional thoughts (Purdon and Clark
2000). Using a scale that explicitly distinguishes thought suppression attempts from successful thought suppression in clinical research on risk factors for experiencing obsessive intrusive thoughts may show if individuals who are at higher risk for obsessive intrusive thoughts are indeed less successful at thought suppression and more vulnerable to the rebound effect (Purdon and Clark
2001). To date this is an unresolved matter that lies at the heart of understanding the obsessive nature of OCD patients.
This study has some limitations. First, a sample of community-dwelling senior citizens was used, which limits generalizing to other populations. However, this particular sample was deemed appropriate to assess relatively active thought suppression processes without the disadvantages inherent of investigating a clinical sample. In addition, having replicated Rassin’s (
2003) findings that used undergraduate students and less advanced statistical techniques, brings additional validity to the three-dimensional solution of the TSI and suggests the solution may be unsensitive to age differences. A second limitation is that the external validity of the present study is limited because only a self-report assessment was employed.
More replication studies are needed to confirm the dimensionality of the TSI, using samples drawn from multiple populations and clinical populations in particular, as the TSI may be of special importance to clinical psychological research. In addition, research on patient populations that are characterized by experiencing uncontrollable thoughts or inadequate thought control in general should use the TSI to be able to differentiate between thought suppression and successful thought suppression. This may shed light on when thought suppression may lead to the rebound effect, who is most at risk to experience the rebound effect and what role (unsuccessful) thought suppression plays in disorders related to intrusive thoughts and obsessions.
It is concluded that the TSI indeed consists of the three dimensions suggested by Rassin (
2003). However, as several items appeared to have some shortcomings, it is advised that future research critically evaluates the weaker items in order to either reword, replace or remove them. In addition, the predictive validity of the three dimensions must be studied prior to considering adopting the TSI in clinical practice.