Data: Data Dirstiributions Flashcards
What does data distribution do
- describes how the data is spread out
What are the key features of a normal distribution graph
- Bell-shaped
- mean, median and mode are all on the centre point
- symmetrical
- 50% of scores are to the left and 50% to the right of the mean
- the end points or ‘tails’ meet the x-axis
When do skewed distribution occur
- When the distribution curve isn’t symmetrical
- meaning that the mean, median and mode all lie in different places
What are the 3 types of distributions
- negatively skewed
- normal (no skew) distribution
- positively skewed
Which is the positive and which is the negative skew
What is a ‘ceiling effect’
- when data plotted from a test that is too easy causes a skewed distribution
- because most people got a high score
What is a ‘floor effect’
- when data plotted from a test that is too difficult causes a skewed distribution
- because most people got a low score
Describe the relationship between the mean, median and mode for a positive skewed distribution
The mode is LESS THAN the median, and the median is LESS THAN the mode
Describe the relationship between the mean, median and mode for a negatively skewed distribution
- The mean is LESS THAN the median, and the median is LESS THAN the mode
What % of scores are found less than ONE standard deviation each side of the mean
68%
What % of scores are found less than TWO standard deviation each side of the mean
95%
What % of scores are found less than THREE standard deviation each side of the mean
IQ is believed to be normally distributed. One standard deviation is 15 IQ points and the mean is 100. What % of the population should have an IQ in the range 85 to 115 IQ points
68%
Fr?
Ong
