Charts can tell the truth and still leave you with the wrong idea. Every picture of a building’s prices shows some facts and hides others. Here are four common pictures, what each one shows, what it hides, and how to read them with care.
The line chart
One line runs from left to right, usually joining the average or median price for each month. It shows the direction of prices quickly. It hides the number of deals at each point, so a month with one sale looks the same as a month with twenty. It hides spread too, because a line has no width. Ask how the line was drawn: a median ignores one odd sale, and an average follows it. Some charts also smooth the line, which removes sharp turns that did happen. A line depends on its source as well. dataHabibi, for one, draws each building’s history from registered sales rather than listings, so every point comes from a deal that closed.
The scatter of individual deals
Each dot is one sale, placed by date and price. A scatter shows spread, odd deals and quiet stretches with few sales. It hides the trend when dots are few, and the eye tends to fix on one high dot. A high dot may be a penthouse, not a rise in the market. Dots also mix flat types, so a studio and a three-bedroom flat can sit side by side. Colour or shape can separate them, and price per square foot reduces the effect of size. A gap with no dots means no sales, not a steady price.
The range band
A shaded band runs between a low and a high value for each period. Some bands cover every sale, and others cover only the middle half. A band shows how wide prices spread and whether the spread narrows or widens over time. It hides the count and the exact deals. Check which kind of band you are looking at, because one odd sale stretches the first kind and leaves the second kind alone. For example, in an imaginary building the March band may run from AED 900,000 to AED 1,100,000 and the April band from AED 950,000 to AED 1,000,000. The narrower April band may mean that prices came closer together, or only that fewer flats sold.
The simple table
A table lists, for each month or quarter, the number of deals and the low, middle and high price. A sample row reads: March, 12 deals, low AED 900,000, middle AED 1,000,000, high AED 1,100,000. A table hides the shape, since turns and trends are hard to see in a column of numbers. It shows what charts often leave out: exact figures and counts. Read the count column first, then the prices. Keep the same columns each month, so you can read every month against the last. Use the table to check any chart you doubt.
How axes can mislead
Whatever the picture, read the axes first. For example, if the vertical axis starts at AED 2,000,000 instead of zero, a rise from AED 2,000,000 to AED 2,100,000 fills the whole chart. A time axis that squeezes five years into a narrow chart makes a slow rise look steep. A chart with two vertical axes brings another trap: when one line uses the left axis and another uses the right, the point where the lines cross means nothing. You cannot compare two charts with different scales by eye. Ask three things: where the vertical axis starts, what one step on each axis means, and whether the price shown is the total or per square foot.
No single picture is enough. A line shows direction, a scatter shows deals, a band shows spread and a table shows counts. A platform can place the line above, the individual deals below it and a small count under each month, so one screen covers direction, deals and the number behind each point. The cost is clutter, so look for clear labels and few colours. To judge these pictures on real data, pick a building at datahabibi.ae.
