If you’re studying Abnormal Psychology as one of your options in IB Psychology it’s important that you can explain differences in prevalence rates.

  • In the old syllabus you have to: Discuss cultural and gender variations in the prevalence of (one or more) disorders.
  • In the new syllabus it just states: Prevalence rates and disorders

The key here is much like my advice on how to explain an etiology of a disorder. In fact it’s just the same – explaining differences in prevalence rates is just explaining how a variable influences behaviour.  


What is prevalence?

Prevalence means how common something is. For disorders, a prevalence rate is the % of a population (e.g. country) that has a particular disorder. A lifetime prevalence rate is the % of a population that is expected to be diagnosed with the disorder at some point in their lifetime.

You can find some interesting prevalence statistics here.


Explaining Gender Differences

If you are explaining a gender difference in the prevalence of a disorder, you’re probably explaining why it’s more common in females than males, because the most common disorders studied in IB Psychology (depression, eating disorders and PTSD) generally have higher rates of diagnosis for females. So you can explain why females are more likely to get the disorder (or why males are less likely).

The key to explaining gender differences is to identify the variable that is different between males and females that can then lead to more symptoms. 


PTSD Example: The variables are self-efficacy and sense of threat

Even though males are more likely to be exposed to trauma, females are more likely to develop PTSD (read more). The example we look at to explain this in the textbook (IB Psychology: A Student’s Guide) is the prevalence of PTSD symptoms in Israeli males and females in the early 2000s after the Second Intifada series of terror attacks. This study (Solomon et al, 2005: Is Gender Terror Blind? Link) identifies two important variables that are different in their male and female participants. One of these was self-efficacy: the males had a higher belief in their abilities to overcome and deal with the issues they were facing. We now have to connect this to how it might explain less PTSD symptoms. Alternatively, we could explain why low self-efficacy in this manner could increase the risk of PTSD.

  • High self-efficacy could result in top-down appraisals of situations that reduce anxiety and stress, since the person thinks “I can deal with this.” Over the long-term their stress response is less active, so symptoms associated with high arousal (one key category of PTSD symptoms) are less likely.
  • Low self-efficacy could result in appraisals that are likely to increase anxiety and arousal, since it activates the stress response if we feel we are threatened and can’t deal with the situation. Over a long period of time, this could have negative psychological and physiological effects which could lead to symptoms associated with arousal or avoidance (e.g. females might avoid places they are likely to feel anxiety).

From the explanations above, you can see that all we’re doing is explaining how one variable (self-efficacy) can possibly lead to symptoms of PTSD. All we’re doing is identifying the variable that’s different in males and females.


Exam Tip

If we can do this, now we also have a psychological etiology of PTSD – simply identify the self-efficacy as the psychology (i.e. cognitive) variable that you’re focusing on and you can use the same study to support your argument.

What we can see here is that the two topics in the new abnormal option for etiologies of disorders (prevalence and explanations) are pretty much the same – reduce your content and maximize your chances of writing an excellent exam response!


Example #2: Cultural Differences 

As with gender differences, we should begin by identifying the prevalence difference when discussing social or cultural differences. Numerous studies have shown that PTSD is more likely to develop in racial minorities (read more). This has been shown in war veterans and after natural disasters.

The variable that we identify in the textbook that explains this difference is socioeconomic status. This can explain the different levels of stress that a traumatic event can inflict. For example, if a hurricane hits and you’ve got a lot of money, it’s much easier to rebuild your life and the impact of that hurricane is going to be less stressful than if you don’t have much money. This can be shown in a number of studies, including Garrison’s et al. (pg. 240-241 of the textbook).

Katrina Levee Breach
A natural disaster (like Hurricane Katrina) would be a lot more stressful for poor people than it would be for rich people. This could explain differences in appraisals of the event and thus, differences in prevalence of PTSD as a result.

Once again we see that explaining prevalence and explaining etiologies is the same argument = how does the specific variable increase the likelihood of developing PTSD.


I hope this post can you help you study smarter, not harder.