The graph illustrates information about the results of a poll of theatregoers regarding disturbances during theatre performances. In general the 4 most disturbing problems are coughing, rustling sweet papers, whispering and arriving late. Their percentages stand at above 50%.
Thanks to the context setting at the start of the essay, I can see that 50% means 50% of the theatregoers who took part in the poll. But it’s not immediately obvious and I had to read the opening a second time to make sure I understood what you meant. If a text is difficult to understand then it will receive a low score in IELTS for coherence and cohesion (CC). In the example above it can also affect your score for task achievement (TA), because you don’t really say anything meaningful about ‘50%‘. (See IELTS Task 1 Writing band descriptors)
A good strategy to introduce and develop percentages in IELTS Task 1 can be seen in this extract from an article in The Economist (analysis below):
What is ‘good’ about this reporting of percentages?
 The first percentage is expressed using the following pattern:
x% + of + noun (‘male characters’) + verb (‘were seen dressed..’)
Notice that the reader knows exactly what is meant by ‘male characters‘ thanks to the clear context setting of the opening sentence. Setting a context like this makes your writing coherent. When you use this structure you explicitly state the ‘whole’ – in this case ‘male characters’.
 The second percentage obviously also applies to ‘male characters’, and so there is no need to repeat ‘..of male characters’.
 ‘Those figures’ signals back to the previous two percentages, which we understand refer to ‘male characters’. Notice the structure:
past time expression (‘In 2014’) + subject (‘those figures’) + ‘stood at‘ + x%
 ..follows the structure:
x% + of + noun (‘male characters’)
 ..follows the structure:
x% + of + noun (‘female characters’).
We’re not surprised to read ‘female characters’ because this new context was set in the opening sentence of the paragraph. Again, this context setting makes your writing both cohesive and coherent since you explicitly state the whole (now ‘female characters’).
Whatever you do..
Make sure your first mention of a percentage includes an explicit reference to the whole:
x% + of + noun (the whole)
Would anybody like to try and re-write the text about theatregoers to make the ‘50%’ figure mean what it’s supposed to mean? Answers in comments below! 🙂
PS. Another example of what I’m talking about just came to my attention: