As epidemiology seems to be taking over the news I thought I’d provide a little glossary of phrases that are appearing in the media in the context of the #COVID-19 pandemic but that you might not have a good working definition for. #COVI19 @ConversationUK https://theconversation.com/how-to-model-a-pandemic-134187

Lets start with MODEL – This is perhaps the most important phrase to understand even though it seems like the simplest. Models, mathematical or otherwise, are a good (but never perfect) representation of reality.

Models are simplified versions of reality and consequently will not get everything exactly right. The hope is that they get the important things right. Part of the scientific process is that models get updated in light of new evidence.

Changing your predictions based on new data is not a sign of weakness, but a sign of strength. This is how science moves forwards. There is nothing to be gained from sticking your flag in the sand and trying to defend your position as the tide of evidence washes in around you.

S-I-R (pronounced as initials not ‘sir’) MODEL - One of the simplest mathematical models of disease spread splits the population into three basic categories. People who have not yet had the disease are “susceptibles”. Those who have contracted the disease are the “infectives”.

The third group are “removed” class - people who have had the disease and recovered and are now immune, or those who have died. The “Oxford” modelling paper used an SIR model to come to it's conclusions, but the "Imperial" model used a more complex variety.

THE BASIC REPRODUCTION NUMBER. Often written R₀ (pronounced R-nought or R-zero) - The average number of previously unexposed individuals infected by a single, freshly introduced disease carrier during their infectious period.

If a disease has an R₀ less than one, then the infection will die out quickly as each infectious person passes on the disease, on average, to less than one other. The outbreak cannot sustain its own spread. If R₀ is larger than one then the outbreak will grow exponentially.

EXPONENTIAL GROWTH – When a quantity grows in proportion to its current size it is said to be growing exponentially. Exponential growth is characteristic of the initial phase of the infection because the more infected people there are the more they create.

Things can change extremely rapidly under exponential growth. We are seeing the implications of this rapid change in the lock-down measures enforced around the world, that even a couple of months ago, no-one saw coming.

HERD IMMUNITY - the concept that a large population of immune individuals can slow or even halt the spread of the disease. The immune individuals are in the removed class and no longer run the risk of contracting the disease if they meet infective individuals.

CASE FATALITY RATE - The proportion of infected people who ultimately die from a disease is known as the case fatality rate. This tells us, on average, how serious a disease for those that contract it.

There are probably many more important terms I have missed off the list, but I hope these ones are useful. If you have more you want me to add then please let me know. You can find more detail in this article if you're interested in How to Model a Pandemic https://theconversation.com/how-to-model-a-pandemic-134187