Why is it so hard to buy a home? Prices have far outpaced middle-class incomes. Mortgage rates are still above 6%. And 3 out of 10 homes are sold above listing price.But none of those factors fully captures the variety of challenges buyers nationwide face in the current market. The conditions on the ground can vary widely across state and even county lines.To better capture how housing market conditions shift at the local level — as comprehensively and in as close to real time as possible — we’re introducing a monthly gauge: the NBC News Home Buyer Index.The Home Buyer Index, which NBC News developed with the guidance of a real estate industry analyst, a real estate expert from the Federal Reserve Bank of Atlanta and other experts, is a number on a scale of 0 to 100 representing the difficulty a potential buyer faces trying to buy a home. The higher the index value, the higher the difficulty. A low index value, of 10 for example, suggests better purchasing conditions for a buyer — low interest rates, ample homes for sale. 02:26A high value closer to 90 suggests extremely tough conditions, which can result from intense bidding, high insurance costs or steep jumps in home prices relative to income.The index measures difficulty nationwide, as well as on the county level, in the counties where there’s enough homebuying data to make informed assessments.The national index, presented below, captures the big-picture market and economic conditions that affect homebuying across the United States.The index consists of four factors: Cost: How much a home costs relative to incomes and inflation — as well as how related expenses, such as insurance costs, are changing. Competition: How many people are vying for a home — and how aggressive the demand is. This is measured through observations including the percentage of homes sold above list price and the number that went under contract within two weeks of being listed. Scarcity: The number of homes that are on the market — and how many more are expected to enter the market in the coming month.Economic instability: Market volatility, unemployment and interest rates — reflecting the broader climate in which home shoppers are weighing their decisions. For March, the national Home Buyer Index was 72, up from February and down 7 points from where it was this time one year ago.The index typically updates monthly on the last Thursday of the month. The next update is May 28.