Many studies have tried and failed to determine the cause of this.

Several economic studies have tried to measure just how much a good school is worth on the real estate market.

What do think all these studies are trying to do?

Several studies have tried to confirm the claim but found no effect.

The current study did not try to estimate total error rates.

The study did not try to measure the number of people using the Internet.

The study did not try to measure improvements in health care because of better access to patient information.

However, only rare studies have tried to prove the point.

Recently, several studies have tried to see such medieval sites in context.

The study does not try to guess where these people might go.