What does 'causal experiment' or 'causal link' mean?

Question

College science course...I stink at science and need all the help I can get!

Answer 1

This is probably making the distinction between causality and correlation.  A causal relationship is where one thing directly causes something else to happen.  Such an experiment would demonstrate this cause and effect.

Correlation is where you observe two things which seem to correspond, but there is no causal link.  There's an old expression, "Correlation does not imply causality."  As scientific principles go, this is a *very* good thing to remember.  Very often, a researcher will claim a causal relationship when the correlation is due to a momentary coincidence or poor controls.  Sometimes it's due to outright manipulation or fraud.

Example: a nurse-turned-witchdoctor takes a one-day class and spends the rest of her career in cancer wards, waving her hands over people's bodies.  They want the data.  Sure enough, while 40% of the patients treated in the clinic over a periood of a year died during that time, only 20% of the ones she "treated" died.  Looks like an impressive cause and effect.  This hand waving thing must really work.  Then you dig closer and see that she only used stage I and II patients in her study, while skipping all the stage III and IV patients.

That's why, in any study where statistics are being used, you have to look VERY carefully at the controls and procedures, especially if someone is making an extraordinary claim.

Note: Despite its increasing popularity, this therapeutic hand waving is superstitious BS.  Why they allow these quacks within 100 yards of a hospital, I'll never know.  They might as well institute Voodoo.

Oh, causal link.  For thousands of years, people noticed that most plants grew better when they had more sunlight.  The correlation was very strong.  But until modern chemistry came about, the causal link was missing.  We have now learned how a plant converts the sun's energy (and carbon dioxide and water), into simple sugars which give the plant energy for growth.  The causal link was established.  It is photosynthesis.