Probability and significance Flashcards
What does all statistical tests work on the basis of?
Probability rather than certainty. All statistical tests employ a significant level.
Define the term significant level.
The point at which the researcher can claim to have discovered a significant difference or correlation within the data.
Point at which researcher can reject the null hypothesis and accept the alternative hypothesis.
State the usual level of significance in psychology.
0.05 (or 5%).
How can you check for statistical significance?
Calculated value must be compared with a critical value.
Define the term critical value.
A number that tells us whether or not we can reject the null hypothesis and accept the alternative hypothesis.
List the different critical values.
One-tailed or two-tailed.
Degrees of freedom (df).
Level of significance.
When do you use a one-tailed test?
If your hypothesis was directional.
When do you use a two-tailed test?
For a non-directional hypothesis. Probability doubles when two-tailed tests are being used as they are a more conservative prediction.
What’s the stringent level of significance?
0.01 (or 1%).
Why are stringent levels of significance used?
It’s when there may be human costs such as drug trials or ‘one-off’ studies that couldn’t be repeated in the future.
Why are type I and type II errors used?
As the probability level used is never 100%, there is always a chance that the researcher may mistakenly accept on of the hypothesis.
What is a type I error?
Is when the null hypothesis is rejected and the alternative hypothesis is accepted when it should have been the other way around.
False positive
What is a type II error?
Is when the null hypothesis is mistakenly accepted, so the alternative/experimental is mistakenly rejected. We are likey to make a type II error if the significant level is too lenient e.g., 1% (0.01). A 5% level is a good balance of the risk of making a Type I or Type II error.
