Standard Deviations And z Scores Flashcards
Are human and non-human characteristics measured on the same scale?
No they are measured on many different scales
Why do we need Standard Deviation?
In research, things can be measured on so many different scales which causes a problem in terms of comparability. Standard deviation makes a number that can help us easily standardised the results and compare them.
What is standard deviation?
It is a standard unit of measurement in statistics. Conceptually it is the ‘average’ amount by which the scores differ from the mean.
What does the standard deviation give us?
The average amount of deviation from the mean.
What is a z-score (standard score)?
This is the term used for how much a unit differs from the mean using standard deviation. If the standard deviation is 7 and a persons score is 21 points above the mean then they would have a z-score of 3 because 7 goes into 21, 3 times.
How do you calculate the z-score?
Calculated by subtracting the mean from a given value and then dividing this by the SD
What do the +/- signs mean in z-scores?
Whether the z-score is above or below the mean
What is one of the major challenges in statistics?
Standardisation
When all the z-scores are put together what is their mean and SD?
Mean = 0 SD = 1
In a normal distribution, z-scores above +/- 1.645 indicate what?
The extreme 5% of the distribution
What are the percentages for a z score of 1 and 2 and higher?
1 = 34% 2 = 14% Higher = 2%
How do you make inferences from z scores?
If something is normal then their score should reside between1 and 2 z scores, if its not normal then it will be higher
If the p value is less than 5% what do we do with the null hypothesis?
We reject it. Shows that something happened
