One of the first studies on intrusive thoughts in the general population was the 1978 paper published by Rachman and De Silva, titled: “Abnormal and Normal Obsessions”. It was a fairly simple study—they gave a questionnaire about intrusive thoughts to eight patients with OCD and 124 other people (mostly students and university staff). Then they compared the answers.
99 of the 124 people in the non-clinical group reported similar thoughts and images to the clinical patients. Or as the paper puts it: “79.84% of the total sample of normals were positives.” Oh, you normals…
Further studies with larger sample-sets tend to get us into the 90%+ range.
Intrusive thoughts about terrible things are way beyond normal.
What you might be most interested in are the types of thoughts “average”, non-clinical people report. It’s all of the classics!
That 1978 study contained two lists of the thoughts and impulses from the clinical and non-clinical sample groups.
For the non-clinical group, they listed 58 thoughts and impulses. Those include some familiar hits: The impulse to hurt someone, uncertainty about calorie content, worry about harming a loved one, the urge to say inappropriate things, memories of a past failure, fear of harming themselves, etc. You can find the full list of quotes on pages 237 – 238.
In the Radomsky et all study, they used a questionnaire with over 100 questions and seven theme groups of intrusive thoughts: “Contamination, harm/injury/aggression, doubt, religious/immoral, sexual, victimization, and ‘other’ intrusions”. You can find that description on page 3 of the study.
Purdon and Clark categorized intrusions into three categories:
• Aggressive thoughts and behaviors
• Sexual thoughts and behaviors
• Disease/dirt/contamination thoughts
Page 715 describes their 52 item Obsessional Intrusions Inventory and the three categories. The 52 item inventory is a list of intrusive thoughts, such as:
• Driving into window
• Running car off road
• Hitting animals / people
• Swerving into traffic
• Smashing into objects
• Slitting wrist/throat
• Cutting off finger
• Jumping off high place
• Fatally pushing stranger
and so on…
The 2004 study by Belloch et al further researched the OII from Purdon and Clark, interviewing 336 non-clinical participants, of which 99.4% had intrusions “occasionally”.
They defined “non-clinical” as no reported psychiatric illness or accessed psychiatric services in the past year. Based on that criteria, they state: “…we can conclude that all of them were currently healthy.”
Meh. One of the reasons for starting TOOLKIT was precisely because not accessing a diagnosis or mental health services does not mean we’re mentally healthy. We need to proactively be building mental health and fitness if we want to be healthy, just like we need to proactively be building physical fitness.
That definition they used is a reflection of the illness-first approach we take to mental health as a society. But it’s a fairly common approach people would see as “normal”. So “non-clinical” basically means: your average person who probably doesn’t take care of their mental health.
Based on the Radomsky et al study that looked across multiple countries, giving us the broadest scope of all the studies mentioned, over 90% of people experience the types of thoughts we typically label as “intrusive thoughts”.
We conclude two things from this:
1) It is rare to have mental fitness skills. It’s not average to practice non-judgment. If we take it that brains throw up intrusive thoughts so we can control core fears like death and abandonment, then these numbers suggest few people have worked on those big fears. That makes sense. There’s no reason we would have those skills unless we intentionally learn and practice them.
2) It’s not the presence of the thoughts (or their absence) which determines struggles with mental illness. Thoughts about uncertainties and terrible things are far more normal than even just a simple majority. They’re beyond average. They’re just human.
It’s common on mental health forums, especially OCD forums, to see regular posts complaining that people without OCD can’t understand what it’s like to have these terrible horrible worstest intrusive thoughts. However, there’s a long list of research demonstrating that nearly all people have these types of thoughts.
Don’t take that as invalidating. It’s useful to recognize if we want to work on recovery from mental illness. Instead of chasing a magic soap to clean away thoughts, we need to shift our focus to learning healthier ways to interact with the stuff in our heads.
Here is just some of the research studying how common these types of thoughts are in human brains:
Belloch, A., Morillo, C., Lucero, M., Cabedo, E., & Carrió, C. (2004). Intrusive thoughts in non-clinical subjects: The role of frequency and unpleasantness on appraisal ratings and control strategies. Clinical Psychology and Psychotherapy, 11(2), 100-110.
Berry, L. M., & Laskey, B. (2012). A review of obsessive intrusive thoughts in the general population. Journal of Obsessive-Compulsive and Related Disorders, 1(2), 125-132.
Clark, D. A., & Purdon, C. (2009). Mental control of unwanted intrusive thoughts: A phenomenological study. International Journal of Cognitive Therapy, 2(3), 267-281.
England, S. L., & Dickerson, M. (1988). Intrusive thoughts: Unpleasantness not the major cause of uncontrollability. Behaviour Research and Therapy, 26(3), 279-282.
Langlois, F., Freeston, M. H., & Ladouceur, R. (2000). Differences and similarities between obsessive intrusive thoughts and worry in a non-clinical population: Study 1. Behaviour Research and Therapy, 38(2), 157-173.
Purdon, C., & Clark, D. A. (1993). Obsessive intrusive thoughts in nonclinical subjects. Part I. Content and relation with depressive, anxious and obsessional symptoms. Behaviour Research and Therapy, 31(8), 713-720.
Rachman, S. (1997). A cognitive theory of obsessions. Behaviour Research and Therapy, 35(9), 793-802.
Rachman, S., & de Silva, P. (1978). Abnormal and normal obsessions. Behaviour Research and Therapy, 16(4), 233-248.
Radomsky, A. S., Alcolado, G. M., Abramowitz, J. S., Alonso, P., Belloch, A., Bouvard, M., … & Wong, W. (2014). Part 1—You can run but you can’t hide: Intrusive thoughts on six continents. Journal of Obsessive-Compulsive and Related Disorders, 3(1), 269-279.
Salkovskis, P. M., & Harrison, J. (1984). Abnormal and normal obsessions—A replication. Behaviour Research and Therapy, 22(5), 549-552.
Trinder, H., & Salkovskis, P. M. (1994). Personally relevant intrusions outside the laboratory: Long-term suppression increases intrusion. Behaviour Research and Therapy, 32(8), 833-842.
Wells, A., & Morrison, A. P. (1994). Qualitative dimensions of normal worry and normal obsessions: A comparative study. Behaviour Research and Therapy, 32(8), 867-870.
