RM - Probability Flashcards
What are statistical tests based on?
Probabilities.
Alternative hypothesis
A testable statement about the relationship (difference, association etc.) between two or more variables.
Null hypothesis
An assumption that there is no relationship (difference, association, etc.) in the population from which a sample is taken with respect to the variables being studied.
Probability (p)
A numerical measure of the likelihood or chance that certain events will occur. A statistical test gives the probability that a particular sample did not occur if the null hypothesis for the population was true, i.e. there was no real effect.
Type I error
Occurs when a researcher rejects a null hypothesis that is true.
False positive.
Type II error
Occurs when a researcher accepts a null hypothesis that was not true.
False negative.
What does chance refer to?
Something with no cause. It just happens.
What level of probability is used in psychology?
0.05
What does it mean that in psychology we use a probability level of 0.05?
This expresses the degree of uncertainty. It means that there is a 5% chance of the results occurring if the null hypothesis is true (i.e. there is nothing going on). In other words, a 5% chance that the results would occur even if there was no real difference/correlation between the populations from which the samples were drawn. This 5% chance is recorded as a probability (p) = 0.05. In fact the chance is 5% or less which is written as p ≤ 0.05.
What is the symbol for probability?
Probability (p)
What does the level of probability express?
The degree of uncertainty.
What is the chosen level of p called?
The significance level.
What level of significance is used in some studies where psychologists want to be more certain?
p ≤ 0.01
1% or less
Why do psychologists generally use the 5% probability level?
Because this is a good compromise between being too strict or too lenient about accepting the null hypothesis - or, more formally, a good compromise between a Type I error and a Type II error.
