10.6 representing variation graphically

discontinuous variation

• a characteristic that can only result in certain values

• often variation determined purely by genetic factors

• eg. sex, shape of bacteria, human blood groups

• may be shown by a bar chart or pie chart

continuous variation

• characteristic that can take any value within a range

• there is a graduation between one extreme to another of a characteristic - this is known as a continuum

• eg. height and mass

• characteristics that show continuous variation are often controlled by many genes as well as environmental factors

• data with continuous variation can be collected in a frequency table and plotted in a histrogram

normal distribution curve

• the mean, mode and median are the same

• the distribution has a characteristic ‘bell shape’ which is symmetrical around the mean

• 50% of values are less than the mean and 50% of values are over the mean

• most values lie extremely close to the mean value - the number of individuals at the extremes is very low

standard deviation

• a measure of how spread out the data is

• the greater the standard deviation is, the greater the spread of data

• in terms of variation, a characteristics which has a high standard of deviation has a large amount of variation

spearmans rank correlation coefficient

• no correlation - no relationship between the data

• positive correlation - as one set of data increases in value, the other set of data decreases in value

• negative correlation - as one set of data increases in value - the other set of data decreases in value

students t test

• used to compare the mean values of two sets of data

• to use this test the data must be normally distributed and enough data must be collected to give a reliable mean