Certainly, social-psycology isn't as certain as hard sciences. One problem, is that in some ways, they are much more complex than the hard sciences. So, to reach the kind of conclusion and laws that you get in hard sciences, they need much more data. Certainly, we can't draw any firm conclusions from this one study, but doing a bunch of similar studies, over several centuries (note that this study took 75 years), might lead to the start of social science becoming a hard science.

Not actively disagreeing, but would you care to elaborate on why you think social-psychology is a psuedo-science?

In his book (http://www.amazon.com/Statistical-Models-Causal-Inference-Di...) Professor Freedman says one of the reasons the social sciences have had virtually no beneficial impact on society (as opposed to the incredible progress in the hard sciences) is that their "studies" have unsupported mathematics. They make too many assumptions, and their methodologies don't support their conclusions. For example, you can do a study on the top reasons teens use drugs, and in a decade those reasons have completely changed because of the shift in culture.

The social sciences don't work well with the scientific method. You can't randomly select people, and you can't get them to make long-term changes to their lifestyle. Without experimental evidence, you are left with observational data, which is a nightmare to find causation instead of just correlation.

You are conflating multiple issues here: whether social science studies are valid, whether the effects of social science are beneficial to society, whether passing some "scientific method test" is a requirement for an approach to be "good."

To take one example (of many), all of consumer marketing is an outgrowth of social science - nowadays consumer marketing, behavioral psychology, and behavioral economics are overlapping fields which happen to go by different names.

We might debate whether marketing has been "beneficial," but I don't think you can reasonably argue that all marketing doesn't work just because the math behind it isn't as rigorous as quantum mechanics. (Not that we completely understand quantum mechanics.)

Consumer marketing would be a good example of something that has no long-term benefit because society changes too often. Marketing techniques that work in one decade won't work in the next. Because of this, marketing isn't cumulative. Our knowledge of the hard sciences is always improving, building on the work of the previous generations.

Yes, there are legitimate fields that don't have rigorous math behind them, but the social sciences try to use studies and numbers as the foundation of their theories. They want to be treated like biology, but their studies are not up to par.

Astronomy is a hard science and it has the same issue. You can't randomly select celestial bodies and experiment on them. However, we seem to have made huge strides in our understanding of the cosmos.

All hard sciences have sufficient evidence to back them up. Whether it is mathematical proofs, experimental evidence, etc. There is no hard evidence for the social sciences. Astronomers can predict orbits with incredible accuracy millions of years into the future. Social sciences haven't been able to create a single useful model.

Also, you said, "However, we seem to have made huge strides in our understanding of the cosmos." That is very different from the social sciences. I don't think we know anything more about human nature today than Shakespeare did in the 1500s.