Attention, Philadelphians: Your city government is conducting experiments to better understand how to get you to react.

As part of an  effort to use human behavior to inform how City Hall reaches residents, a group led by Mayor Kenney's policy team conducted three studies, the results of which were made available last week.

The team: Director of Policy Anjali Chainani, Assistant Director of Policy Yuan Huang, and Policy Analyst Nandi O'Connor. They run GovLabPHL, which connects volunteer researchers from the University of Pennsylvania and Swarthmore College with various city departments. In its first round of testing, GovLabPHL worked with the city's Revenue Department, Indego bike share, and a summer jobs program.

Some of the experiments may seem simple, but they are shaping how departments go about mail and email campaigns to maximize responses and participation.

"We're doing this because we have a commitment from the policy office to lead with research and evidence," Chainani said. "All these departments really believe in being able to use scientific methods to see if their outcomes work, primarily because we do the best we can with the resources we have, but we can't always know exactly what is working until we test it."

The Revenue Department focused on first-time delinquent taxpayers. The office sent different messages to see which drew the most responses. The first letter appealed to the person's civic duty, citing specific parks and recreation centers in the neighborhood supported by property taxes. A second letter sought to shame recipients by pointing out that nine out of 10 Philadelphians pay taxes and that they were in the tax-dodging minority. The final and most effective message listed all the properties in the neighborhood that had been sold at sheriff's sale because of unpaid taxes.

"The scary letter -- warning of impending consequences -- was by far the most effective," First Deputy Revenue Commissioner Marisa Waxman said. "We've really learned through this work that everything is a choice. Not thinking about how you're structuring or delivering your message is a choice."

The department spent $17,000 on the mailers but collected $615,752 more in delinquent taxes than it did from a control group that received in the mail the standard, less personalized notice of delinquency. If each recipient had received the "scary letter," Waxman said, the city could have reaped $1 million, based on the data.

The Revenue Department also wanted to increase participation in a water bill discount program for senior citizens. In this instance it was the packaging, not the message, that made a difference.

The city found that large envelopes with handwritten addresses received more responses than regular-size envelopes, phone calls or post-cards. Mint- or sage-colored regular-size envelopes also seemed to get people's attention, Waxman said.

In an attempt to find out what motivates children to sign up for summer jobs, Philadelphia Youth Network sent out two types of e-mail reminders -- one that stressed what a job could mean for the young person's career prospects, and another touting the pay.

The city found reminders of any kind helped boost applications, but that teens who received e-mails mentioning money were slightly more likely to submit applications.

The summer jobs program, which Mayor Kenney wants to increase to 16,000 young people by 2020, had 10,600 participants last year.

Indego bike share wanted to increase the rate of renewal among people who sign up for the program. The program e-mailed coupons for 15 percent off to one cohort, coupons for 50 percent off to another, and no coupons to a third. Renewals increased twice as much among coupon recipients as among non-coupon recipients, and the higher discount drew more renewals.

Chainani said the department would work with the Department of Licenses and Inspections on how to get more people to renew licenses online and the school district to increase teacher participation in an annual survey. The city has also applied for a Knight Foundation grant to place two full-time researchers at City Hall.