The cost of living on Martha's Vineyard is about 60 per cent above the national average, and housing costs are almost double, according to a study carried out by the Martha's Vineyard Commission.

Across all indices, or categories measured, from groceries to health care to transport and utilities, the Island was far more expensive than the national average. The standout figure was housing, which scored 196, or 96 per cent above the average.

The survey, carried out last summer using the model of the American Chamber of Commerce Researchers Association (ACCRA), amended in some areas to fit the unique circumstances of the Island, compares relative costs of consumer goods and services "appropriate for professional and managerial households" in the top quarter of the income scale in urban areas across the country. In each of the component indices, the national average cost was set at 100.

Even compared with the inflated costs in Boston - which scored 140 on average across all indices - the Island was an expensive place to live. Housing cost 12 per cent more than Boston.

While the survey methodology relates to the top 25 per cent of incomes, Christine Flynn, the affordable housing and economic development planner, said results in most categories were equally applicable - and even more worrying - for people earning less. Ms. Flynn noted the median household income on the Island is about 20 per cent below that for Boston.

Apart from the housing numbers, which were more specifically applicable to those earning higher incomes, all the indices provided a reasonable approximation of living costs for people of all income levels, she said.

Grocery prices, for example, which affect all income groups more or less equally, were 37 per cent above the national average and 13 per cent above Boston. Utility costs were 52 per cent higher than the national average and 16 per cent above Boston.

Transportation costs were 39 per cent above the national average and 22 per cent above Boston. The cost of miscellaneous goods and services was 44 per cent above the nation as a whole and 10 per cent more than Boston.

The only index on which the Island compared favorably with Boston was health care, which was seven per cent less here, but still 38 per cent above the national average.

The commission cautioned that while the survey gave an approximation of the cost of living on the Vineyard, the number of items surveyed and the number of samples for each item was relatively small and in some cases quite different from those used elsewhere in the country and therefore "not as precise as a [cost of living index] prepared using a more exhaustive methodology."

The report notes a number of limitations of the ACCRA model, including the fact that it focuses on goods and services suitable for managerial and professional households in urban areas, rather than considering consumer goods and services that might be used by a wide segment of the population.

Also, it does not include child care, taxes and some other costs.

Exact comparisons could not be made for some items because they did not exist on the Vineyard - certain categories of housing, for example, and fast food.

"In some cases, the closest possible approximation was provided, such as substituting items that specified a Pizza Hut or McDonald's with local restaurants," the report says.

Some other items, like bowling and Kentucky Fried Chicken, were zero-rated because there were no such establishments on Martha's Vineyard. This caused the cost of living to appear lower on the Vineyard than it actually was, commission executive director Mark London said.

"Zero essentially doesn't say that we don't have KFC, it says we have a KFC, and they give away their chicken for free," Mr. London explained.

Had these items not been zero-rated, the miscellaneous goods and services category would have been 16 points higher, at 160, and the composite index six points higher, at 163.

Even worse, Mr. London said, was the fact that the high prices were not offset by high incomes,

"If we were going to do an affordability gap - if there were some measure of the difference between median incomes and the cost of living across the nation - it would be even more dramatic," he said.

On the positive side, though, there were some offsetting factors relating to the Island lifestyle.

"Some people have commented that it doesn't reflect the fact that there are certain things we don't need here - a suit and tie and so many changes of clothes, for example, that you would need if you were working in downtown Boston," Mr. London said.

And notwithstanding the difficulties of applying the chamber of commerce model to the Vineyard, he said, the survey provided a reasonable guide to the high costs of existing on the Vineyard.

"With each updated index survey, it should be possible to reduce the overall margin of error by enlarging the sample size, making more accurate estimates and dealing more efficiently with the various special circumstances [of the Island]," the report concluded.