The government is being urged to change the way it measures changes in health inequalities to give a truer picture.
People on lower incomes have lower life expectancies
Death rates from diseases like cancer and heart disease are used to show the gap between the health of the richest and the poorest in society.
The government has pledged to improve the health of the most deprived fastest in order to narrow the gap.
But health officials have refuted the British Medical Journal study claims figures are currently misleading.
Study author Dr Allan Low, a health economist at the University of Newcastle, says the Department of Health sets targets, and measures gaps in indicators of health equality, in several different ways which can be confusing.
But where they measure these in absolute terms - ie the gap in rates between two groups in the population, a misleading picture can be given.
Dr Low says health officials should instead consistently measure how one rate has changed relative to the other to accurately reflect the situation.
Dr Low said: "The government are using this narrowing to say we have improved health inequalities when we haven't.
"Relative gaps deal with whether one group has improved compared to the other.
"We have to use relative gaps to get a true picture."
The study highlights Department of Health figures measuring changes in death rates from cancer and circulatory disease that suggests progress is being made in reducing health inequalities.
Official figures suggest the gap between the poorest and the national average had narrowed for cancer and heart disease death rates.
Dr Low also argues that unless the correct measurement of difference is used, the real situation will not be apparent.
"The Department of Health is hoping that most people won't grasp this," he said.
"They've set some really silly targets using absolute gaps. If you translate them into relative terms the targets show the poorest are improving slower."
He added: "It is only if the relative gap narrows that you can say that the health of the disadvantaged has improved faster than everybody else."
But a Department of Health spokeswoman denied there was confusion and said progress against the 12 national headline health inequalities indicators was set out in both relative and absolute terms.
It also said it was clear about the mixture of absolute and relative target measures and that it was determined to reduce health inequalities.
"A report published last year on health inequalities showed that we are moving in the right direction and highlighted the further work that needs to be done," she added
Dr Richard Cookson, health economist at the University of East Anglia, said the paper made a valid point but that different results could always be achieved by cutting the cake in different ways.
"Of course the Department of Health will want to present the most favourable statistic they can find.
"It would be wonderful if we could just meet any of these targets but what tends to happen is that the rich zoom ahead."