There’s been a lot of talk since the healthcare law passed about the success the supermarket chain Safeway has had in controlling costs by aggressively encouraging employees to participate in healthier lifestyles. There has been a lot of marketing and hype and publicity about their success, as well as the success of other employers in the market.

But does such active engagement really work?

The argument for implementing wellness programs and incentives does inherently make sense. There is significant data to support the fact that unhealthy behaviors do contribute to higher healthcare costs. There’s also no question that employees should be held more accountable for their decisions and the impact those decisions have on costs – not just to themselves, but to the employer.

But while financial incentives can be effective in getting people to change behavior in the short term, the challenge is in insuring that employees are consistent.

It is not uncommon for employers these days to make adjustments to copayments and deductibles, based on employee engagement. But the reality is that most employers seldom have the means to measure the cause and effect relationships. They’ve heard anecdotes, alleged success stories, but have not been given data that truly link the impact of their incentives on medical outcomes.

That’s because it is very complicated to bring together all of the necessary data for an employer to be able to measure whether a certain wellness program has truly had an impact on medical outcomes.

Take the case of Safeway, for instance. There have been many reports about Safeway’s success in reducing the trend of health inflation, but when one looks under the covers, the company has many programs in place, none of which are integrated. In addition, there has yet to be published any substantial data to support the notion that their programs have reduced the incidents of chronic disease or utilization of services.

There are many employers who will make investments in onsite clinics, wellness screenings, fitness devices, and spend enormous amounts of money on these initiatives. Without adequate measurement of how engaged a consumer really is, both at home and at work, and accurately linking this data back to clinical outcomes, any claims of success at cost reduction are guess work.

Sreedhar Potarazu is an ophthalmologist and founder and CEO of Vital Spring Technologies. He blogs at Business and Policy.