To know which descriptive and inferential statistics are appropriate for your data you need to be able to work out the level of measurement that has been used. Counting/tallying the number of behaviours or people who fall into different categories is known as nominal data. Data points that are ranked are known as ordinal data and data which is measured in standardised units is known as interval data. When Ainsworth categorised the babies in her studies as Type A, B or C, the data she collected was nominal. Rating the babies’ distress when their mothers left the room on a scale from 1 to 7 would be ordinal data as the babies or order from least to most distressed so this data is ordinal. If she recorded the mother’s heart rate in beats per minute while she listened to her baby crying this would be interval data. NB Ainsworth did not do this but it might have been interesting data to collect!