Expressing opposite trends for IELTS WRITING PART 1

Question

Hello,I have been trying think of a way to refer to a relationship between different trends in the sales of coffee etc as given in an IELTS writing table task. In the table the sale of one item increases (over a time period)compared to another and then the opposite happens. I suggested to the student  that I volunteer with to use the word mirrored.e.g The sales of  the sandwiches and pastries mirrored each other throughout . = meaning that as sandwich sales increased, pastries decreased.I am not sure of the use of mirrored because on the one hand it implies similarity, but on the other it also suggests an opposite action ( we see our left hand in the mirror  as being on the right of the image).I can't use correlation because it has a sense that the sale of one item influences the sale of the other. Any suggestions would be welcome.  thanks

CalifJim · Accepted Answer

I believe the expressions you are looking for are "varies directly" and "varies inversely". I don't think the word "varies" necessarily needs to imply strict proportionality or correlation, so I think you're covered on that aspect of the problem.

CarewThe sales of the sandwiches and pastries ~~mirrored each other~~ varied inversely throughout.

As shown above.

Wait for more suggestions. Someone else may have a better idea.

CJ

AlpheccaStars · Answer

CarewI can't use correlation because it has a sense that the sale of one item influences the sale of the other.

Correlation is used for datasets with enough data points to calculate the correlation coefficient. You have made a fallacious assumption that there is an implied cause, influence or any relations whatsoever between two data sets that are positively correlated.

The word "correlation" is a purely mathematical term. Two curves are positively correlated if they tend to move in exactly the same way. They are negatively correlated if they move in opposite ways. The correlation coefficient is a mathematical calculation that ranges from +1 (perfect positive) to -1 (perfect negative.) These two curves have a negative correlation coefficient of -0.96. These two curves are positively correlated. The correlation just is a measure of "sameness of the patterns." It says nothing about A causing B or B causing A.

That statement is a conclusion or inference, which must be determined by other external evidence. For example, this graph shows a near perfect positive correlation between the number of children with autism and the sales of organic food. It is a conclusion to write that eating organic food causes autism! In this second example, the number of people who kill themselves has a positive correlation with the US budget for science and space technologies. It is a conclusion to write that putting more money this category causes people to commit suicide.

In these two examples, the correlation is true, factual and accurate, but the deduction or conclusion is utterly ridiculous. Many people are deceived into making false conclusions from accidental correlations.

On the other hand, some businesses selling seasonal services or products deliberately pick items whose seasons are negatively correlated. For example, a service company maintains home air conditioning and heating systems. The calls for air conditioning are very high in summer and nearly nothing in winters. The opposite is true for heating systems. By combining both services, the business is steady rather than fluctuating wildly.

In this made-up example, a company sells sunscreen, popular in summer, and umbrellas, popular in winter. The fluctuations in each cancel out to make a smoother trend line for sales.

Expressing opposite trends for IELTS WRITING PART 1

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