Levels of Measurement

• The type of data analysis will depend on what level the measurement is. In Psychology, there are 4 levels of measurement known as Nominal, Ordinal, Interval and Ratio data.
• Nominal data is data that is produced as named categories, think of ‘nom’ meaning ‘name’ i.e. named categories.
• Nominal data is the basic level of measurement, usually displayed in a tally chart.
• Nominal data only tells us how many P’s picked each option or how many were observed in each category, not why.
• Ordinal data is always used with questionnaires, as scores can be placed in order.
• Data which can ranked in order is ordinal.
• Ordinal data is used in most questionnaires and correlational studies.
• If participants have a score on a test or questionnaire, this will be ordinal data.
• If the score on a test or questionnaire is an actual unit of measurement, this will be interval data (like time in seconds/ distance in meters).
• Ordinal data is used when scores can be put into order e.g. 1st 2nd, 3rd.
• Ordinal data cannot tell us what the gap is between positions 1st and 2nd, or between 4th and 5th.
• Interval data is the most complex level of measurement and is not often used in A level Psychology.
• For interval and ratio data there is an equal gap between each unit of measurement. For example, the space between 1cm and 2cms is the same as that between 3cm and 4cm.
• Interval level of measurement has equal intervals between values and a meaningful zero point is absent, while ratio level of measurement has equal intervals between values and a meaningful zero point is present.
• With interval data, zero does not mean nothing, it is just another number on the scale. For example, 0 degrees centigrade does not mean there is no temperature.
• With ratio data, zero does mean nothing. For example, if it took 0 seconds to run a race it took no time.
• Nominal data is usually collected in observations which use categories of behaviour.
• Ordinal data is usually collected in fixed choice questionnaires or interviews or in correlations where numerical scores can be ranked in order.
• Interval data is collected when scores are collected using an apparatus with actual units of measurement.