I think Johor is closer to 15-20% in 2013.
You would be amazed how rough calculations people have for real estate price increases. They will often do things like median sales price from one year to the next with no allowance for changes in mix of sales. This falls into the Simpson's Paradox data understanding failure
https://en.wikipedia.org/wiki/Simpson's_paradox
Paying attention to price/square foot can help some (as one big factor can be large versus small units) but obviously this is far from complete. Luxury condos v. condos v. bungalows v. link-houses will have different price/square feet. Often you will see price increase at least broken out by condo v. landed housing (but not always) and that is not enough for any but very rough general trends. And if someone says the "market" is up 15% they are not breaking the data that way (it is possible both went up 15% but that is rare - more likely there is a huge issues with Simpson's Paradox (and more data issues) if they quote one figure for a market.
If price comparisons are not market transactions of the
same property (which is not often the case) there are all sorts of issues with the data. To think a difference of 10% v 20% increase in prices is significant the very smallest unit of comparison would have to be something like:
- 3+ bedroom condos with over 1,000 square feet in luxury buildings in JB
- 2,000 square foot+ bungalows in high security areas of Nusajaya
- etc
They also have to adjust the median price due to know factors (such as high floor units selling for more, difference between prices of various developments, etc.). You will almost never find this done. They also have to adjust for non-market pricing (for example if prices are inflated for some purpose with artificial givebacks - say to reach a mandated sales price minimum). And while median is the best measure for various reasons (mainly it is least likely to be thrown off by edge cases) there are often big differences between the most expensive, least expensive and other parts of the market...
You also need to consider non-pricing factors. If many people wishing to sell are forced to hold on because they can't get the price they want it can make the market seem much stronger than it is (I don't think the sales market in JB is much more this way than many markets but the rental market is - there are huge numbers of vacant units in JB which is just increasing as more and more units are completed).
This just means the data is extremely rough. And this is even more true in rapidly changing markets; I would classify the luxury portion of the JB market as firmly within the rapidly changing context.
Bottom line is the difference between 10% and 20% quoted price changes in real estate is likely not supported by data. The data likely does not provide enough clarity to distinguish between 10% and 20% on a short term basis (say one year to another). And most of the time it is much more useful to look at smaller segments of the real estate market where you can get a bit clearer picture (though as you get too small it gets to be less reliable due to the small numbers - so it is tricky).
For some reason even most people in the real estate business don't understand some of the simple ideas explained above. This is true worldwide. It is partially explained by the general poor understanding of data by most of people and that often real estate professionals spend most of their time learning sales tactics rather than learning about the real estate market.