Generalizability

(External validity)

is defined as the applicability of the obtained results beyond the cohort that was studied.

It answers "how generalizable are the results of a study to other populations?"

Eg, a study in middle-aged women would not be necessarily generalizable to elderly men.

Internal validity

relates to conclusions regarding cause and effect in a study and answers the question, "Are we observing/measuring what we think we are observing/measuring?"

It intends to specific cohort study.

The major threat to internal validity is confounding.

A statistical hypothesis is an assumption about a population parameter, which may or may not be true

Null = Hypothesis of no difference

Alternative hypothesis states that there is a difference (i.e. rejects the null hypothesis)

Incorrect Results or Errors

Type I error (alpha):

Alpha = You sAw a difference that did not actually exist

i.e. False positive error

Type II error (beta):

Beta = you were Blind to the truth

False negative error