Why is it that studies often seem to contradict each other?

When reading the newspaper, browsing the Internet, or watching the news, we are often told about a new study that found X,Y and Z. A while later, it seems that another story is saying the opposite and that the second group of researchers really found A, B, and C instead.

It can be frustrating to read these seemingly opposite findings, but there are many issues that come into play in a study. First, we have to look at the size of the study group. A small study, of 15 or 20 people, for example, can have a higher false finding rate than a study of 1500 people. The parameters used can also make a big difference. Were the researchers really looking for the same thing, or did they stumble upon a finding and think that it would make interesting news?

If we have a study that says eating chocolate caused cancer in 20 out of 30 people, a much larger study done a year later may find that only 20 of their 1000 people got cancer. So, which study is right? The one with the fewer people that included the 20 unlucky people or the larger study in which there were only 20 unlucky people.

The only way to back up this type of information is to have repeat trials, mimicking the same type of surroundings and issues. This is why it often seems that too many researchers are looking at the same things. This is to back up previously learned information to see if it can be duplicated. If it can be duplicated, we're closer to learning what is right.