NWhat is the range
Tells us how dispersed the data is
A large range indicates the data is very spread out
How do you calculate the range
Subtract lowest from the highest and add 1
What is the variance
Tell us about the spread of scores around the mean
Small variance says scores are all similar and close to mean
A large variance would mean very different and far from the mean
How do you calculate population variance
How do you calculate sample varaince
What are the steps for calculating the population variance
- Calculate mean of scores
- Find the variance by subtracting the mean from each
- Square the resukts
- Add squared numbers
- Divide sum of squares by n
What is standard deviation
The square root of the variance so tells us the average amount a number differs from the mean
A small tells us that the score are very similar and consitent
A large tells us very different and inconsistent
How do you calculate the standard deviation
Square the variance
What are the strengths of both
They take all scores into account, so are more representative measure of dispersion
What is an advantage of SD
Returns the units to the same figure as the mean, easier to make direct judgements about data seats
What is nominal data
Weakest level of measurement
Results are in 2 or more named behaviour categories
Likely to be collected form closed questions
What is ordinal data
Results are placed in rank order eg. 1st, 2nd
The difference between the ranking is not known and does not have to be equal
What is interval data
Most precise level of data
Resukts are made up of numbers that come from a scale of equal or known units with equal distances between the points
It uses precise math units eg weigjt
What level of data do you use when measuring the mode
Nominal then ordinal then interval
What level of data do you use when using the median
Ordinal then interval
What level of data do you use when using the mean
Interval
What is a strength and weakness of nominal level of measurement
+ can conduct statistical analysis and present it in bar charts and pie charts, allowing us to generate conclusions about most commonly occurring category
- without a linear scale pp may be unable to express degrees of response, lowers the insight and so lacks validity
What I’d a strength and weakness of ordinal level of measurement
+ indicates relative values on a linear scale instead of just totals, degree of response so much more informative
- do now know how large the gap is between 1st and 2nd and 2nd and 3rd or if gaps are equal,difficult to make direct comparison as don’t k it differences between value
What is a strengthof interval level of measurement
+ data points can be directly compared as they are each if equal value, allowing us to make scientific conclusions abour data
What is a normal distribution
A bell shaped curve, mean median and mode in centre, 50% scores right 50% scores left
What are the percentages of scores in a normal distribution
-68% of scores fall -1 & +1 SD
- 95% of scores fall -2 & +2 SD
- 99.7% of scores fall -3 &+3 SD
What is a skewed distirbutiom
The spread of data is skewed and is more on one side
The m,m,m will be at different points
What is a positive skew
It is skewed by positvw/high scores
The mean is on the right
Mode is always in at the top
The mean is pulled to the right by extreme high score
What is a negative skew
It is skewed by low scores
The mean is pulled to the left by extreme low scores
