Boys and girls are different heights.
As opposed to:
Boys are taller than girls.
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Give 3 example of cause and effect
Increased levels of atmospheric carbon dioxide might cause global warming.
No. The null hypothesis is not considered correct. It is an assumption, and hypothesis testing is a consistent meand of determining whether the data is sufficiently strong to say that it may be untrue. The data either supports the alternative hypothesis or it fails to reject it. See examples in links. Also note this quote from Wikipedia: "Statistical hypothesis testing is used to make a decision about whether the data contradicts the null hypothesis: this is called significance testing. A null hypothesis is never proven by such methods, as the absence of evidence against the null hypothesis does not establish it."
This would be an hypothesis (an educated guess).
When we've proven that the hypothesis is false !