Version 2 (modified by lxwang, 7 years ago) (diff)




The concept of relational concurrency appears frequently in the literature on HIV epidemiology, and is believed by some researchers to represent a key factor in understanding large disparities in the prevalence of HIV or other sexually transmitted infections (STIs) among populations. On the one hand, the basic logic behind the hypothesis is straightforward; on the other hand, it entails some subtleties that can run counter to many people’s intuition. Thus, it can be somewhat tricky to understand, which has caused some confusion among both researchers and the general public.

The aim of this website is to provide intuitive, easy-to-use tools to help researchers and the general public to understand the concept of relational concurrency and the ways in which it can affect the spread of sexually transmitted infections like HIV. The site contains some introductory overviews, followed by a series of four exercises. The four exercises focus on relational concurrency at the local level and the population level; each level is first explored through a conceptual exercise, and then by a more complex numerical exercise.

The conceptual exercises do not require any special mathematical background, and are geared at providing a basic but powerful understanding of relational concurrency. Some readers may wish to explore only the conceptual exercises. The numerical exercises require some additional background. Specifically, exercise 3 requires an ability to calculate basic probabilities. Exercise 4 requires familiarity with the R programming language. We thus provide a tutorial for each of these components. Readers may wish to try the exercises first, to see if they are able to follow them; if not, they can switch over to the tutorials.

Throughout the exercises, we will use the term “concurrency” as short-hand for “relational concurrency” or “sexual relationship concurrency.” One may see all of these terms in the literature; they mean the same thing.

Introductory Overview

  • What concurrency is (and is not)
  • How concurrency works (and does not)
  • What this website is (and is not)


  • Exercise 1: Thinking conceptually about concurrency at the local level
  • Exercise 2: Thinking conceptually about concurrency at the population level
  • Summary of conceptual exercises
  • Exercise 3: Thinking numerically about concurrency at the local level
  • Exercise 4: Thinking numerically about concurrency at the population level
  • Summary of exercises


  • Tutorial 1: An introduction to the rules of probability
  • Tutorial 2: An introduction to R

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