Probability and significance Flashcards
How do researchers begin their investigations?
By writing a hypothesis
Hypotheses may be what depending on how confident the researcher is in the outcome of the investigation?
Directional or non-directional
What is the alternative to a null hypothesis called?
Alternative hypothesis
What does the null hypothesis state?
There is ‘no difference’ between the conditions
Statistical tests work on the basis of ___________ rather than certainty
probability
All statistical tests employ a ____________ level - the point at which the researcher can claim to have discovered a large enough difference or correlation within the data to claim an effect has been found.
significance
Significance level
The point at which the researcher can claim to have discovered a large enough difference or correlation within the data to claim an effect has been found
The point at which the researcher can reject the null hypothesis and accept the alternative hypothesis is known as…
the significance level
What is the usual significance level in psychology?
0.05 (or 5%)
How is the usual significance level in psychology properly written?
p ≤ 0.05 (where p stands for probability)
The usual level of significance in psychology is 0.05 (or 5%). What does this mean?
Even when a researcher claims to have found a significant difference/correlation, there is still up to 5% chance that it isn’t true for the target population from which the sample was drawn
True/False: Psychologists can never be 100% certain about a particular result
True
Why can psychologists never be 100% certain about a particular result?
They have not tested all members of the population under all possible circumstances
Psychologists have settled upon a conventional level of probability where they are prepared to accept that results may have…
occurred by chance
Once a statistical test has been calculated, the result is a number. What is this called?
The calculated value / observed value
To check for statistical significance, what must the calculated value be compared with?
A critical value
|Critical value
A number that tells us whether or not we can reject the null hypothesis and accept the alternative hypothesis
Each statistical test has its own table of ________ ______, developed by statisticians
critical values
What are the three criteria needed to know which critical value to use?
Whether its a one or two-tailed test, the number of participants in the study or degrees of freedom and the level of significance/p value
When do you use a one-tailed test?
If your hypothesis was directional
When do you use a two-tailed test?
If your hypothesis was non-directional
Why do probability levels double when two-tailed tests are being used?
They are a more conservative prediction
The number of participants in a study usually appears as which value on a table of critical values?
The N value
When may a more stringent level of significance such as 0.01 be used?
In studies where there may be a human cost, such as drug trials or ‘one-off’ studies that could not, for practical reasons, be repeated in future
If there is a large difference between the calculated and critical values in the preferred direction, what is a researcher likely to do?
Check more stringent levels, as the lower the p value is, the more statistically significant the result
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 because, in reality, the null hypothesis is ‘true’
What are Type I errors often referred to as?
An optimistic error or false positive
A Type II error is when…
the null hypothesis is accepted but it should have been the alternative hypothesis because, in reality, the alternative hypothesis is true
What are Type II errors often referred to as?
Pessimistic errors or false positives
When are we more likely to make a Type I error?
If the significance level is too lenient (too high)
When are we more likely to make a Type II error?
If the significance level is too stringent (too low)
Psychologist favour the 5% level of significance as it best balances the risk of making what?
Type I and Type II errors
