Scientists must exercise faith in order to gain knowledge. Here's why....

Evidence is anything that comes to your attention, whether it's something out of a lab experiment or simply a personal experience that you have. Human experience is essentially the evidence we use to develop our beliefs.

You start with evidence, then you build up some belief based on that evidence. Belief, itself, is not faith. Faith is when you act on your belief. Once you act on your belief, you get some sort of feedback as to whether that action (ie faith) was reasonable or unreasonable. That feedback becomes part of your knowledge. Once you get to this point, once you gain knowledge based on your action, you will have additional evidence to support future actions.

Science operates the same way.

Scientists use statistics to build up evidence. They start with a statistical analysis (X is 95% likely to be true) and they analyze those stats to develop a belief hypothesis. Scientists then test the hypothesis, which is the equivalent of a theist acting on his/her belief. Where the Christian might exercise faith in acting on his beliefs, the scientist exercises his faith in carrying out experiments to see if his hypothesis is true. When we collect evidence from that test, we can add the data to our broader range of knowledge and develop a theory.
The theory then becomes the basis for additional experience and evidence, where we can go back into the cycle, refine our understanding, enhance our beliefs and continue to develop increasing knowledge that builds up the scientific enterprise.

Whether it's a Christian acting on a belief or a scientist testing a hypothesis, the process is essentially the same. Both have faith.