measures of central tendacy and graphs and standard dev

measures of central tendency

mean median or mode

measures of dispersion

to what extent is the data spread out e.g. range or standard deviation

graphical representations

• bar chart

• histogram

• tables 

mean advantages

• most sensitive measurement because it uses all data 

mean disadvantages

can be effected by extreme scores and distort the value 

median advantages

• not affected by extreme scores

median disadvantages

not as sensitive as the mean because not all data is used in its calculation

mode advantage

not affected by extreme values

mode disadvantage

not as sensitive because it only shows the most frequent score 

which measure of central tendency do you use 

• mean is normally the most accurate 

• avoid using mode if the data is bimodal 

• do not use median if the data is wide ranging because it wont give a true reflection

range advantage

easier to calculate and understand than other measures e.g. standard deviation

range disadvantage

gives no information about whether the scores are clustered around the mean or spread out

standard deviation

this measures how far each score was away from the mean

• larger standard deviation = scores are very spread out away from the mean 

standard deviation advantage

all scores are used so its a very sensitive measure of dispersion - better than range 

standard deviation disadvantage

more time consuming to calculate than the range

bar chart

• represents categories = discrete data 

• not continuous data on the X axis 

histogram 

• bars touch each other 

• data on X axis is continuous 

scattergram 

only used for correlations 

tables 

show the raw data before any analysis 

normal/symmetrical curve of standard deviation

• the distribution and frequency of scores on the left side matches those on the right 

• height, weight, IQ, blood pressure 

what type of data skew is this 

positive skew

what type of data skew is this

negative skew 

negative skew in a distribution curve

the mode is a higher number than the median and the mean because extremely low scores have distorted the mean