You are correct Richard if you look at the numerical increase. Sure, $1 on $15 is more of a percentage than $1 on $16. But the thing is that if you were negotiating your yearly raise you would not negotiate a numerical increase, you would negotiate a percentage increase.
If you negotiated a 7% increase each year then the actual amount received would increase. If received less then you would start to get a bit miffed as your percentage raise is decreasing.
The same with the WTS. They love to highlight the raw numbers. 8 million publishers, 19 billion hours, 20 million at the memorial, hundreds baptised each day, thousands of congregations.
The fact is however that percentages are important as they tell the real story on things like the efficiency of the preaching work, the conversion rates and so on. The percentages indicate trends that point to the health of the organisation and it's long term viability.
If you are earning $30,000 pa and get a $10,000 pay rise, that's great. It's far less impressive if you are earning $300,000.
The WTS is not an organisation of 1 million bringing in tens of thousands a year. They are an organisation of 8 million, spending almost 20 billion hours preaching yet in the 2014 service year had net increase of 18,000 people. The 2015 service year brought figures like an increase in average publishers of 26 people in the UK.
The WTS hides the reality with the big numbers but the percentages expose the malaise that is infecting the organisation and shows no sign of disappearing.