Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
These provide ways in which the researcher can obtain summary descriptions of sets of quantitative data. 2 types are measures of central tendency, which give average values, and measures of dispersion, which look at the variability of scores. These give a single value that summarises a set of data. However, this also produces a loss of individual information. Measures of central tendency These provide a single value that is representative of a set of numbers by indicating the most typical value. This is your set of numbers: 4, 6, 7, 3, 6, 2, 8, 1, 9, 5, 6, 2, 3. Use the information below to complete your notes (p.47,48,49) Under how to calculate, use these numbers to calculate the relevant value, showing your workings. How to calculate Mean Median Mode This is known as the statistical average and all scores are added up and divided by the number of scores The mean of the set of data given is……………….. Scores are put into rank order, and it is the central score – if there is an even number, the median is the mid point between the 2 scores The median score from the example data is……. The most common number in a set of scores The mode is…. Advantages Makes use of all the data and therefore is the most sensitive measure of central tendency Especially useful if the scores represent a normal distribution Not affected by extreme scores Disadvantages It can be misrepresentative if there are extreme values and therefore this is misleading. e.g. if our set of numbers has 57 in it, the mean is actually ….. Not useful for small sets of data especially if these contain widely varying scores e.g. 7 8 9 102 121 Not as sensitive as the mean because not all the values are not reflected Useful when the data is in categories Not useful when there are several modes (multimodal) Does not tell us about the other values in the distribution Measures of dispersion A single value showing the variation/spread of scores in a set of data. How to calculate Range Standard deviation (use this therefore when the mean is used) The interquartile range This is calculated by taking away the lowest value from the highest value in a set of scores The range value for the example data is…….. This is a measure of the spread or variability of a set of scores from the mean. The larger the S.D, the larger the spread of scores from the mean and vice versa Don’t need to calculate This measures the spread of the middle 50% of values when they are placed in numerical order Don’t need to calculate! Advantages Disadvantages Easy to calculate Affected by extreme values Gives a basic measure of the variation within the data. If there are extreme values therefore it is inappropriate It is a sensitive measure of dispersion as it takes all the data into account Harder/more timeconsuming to calculate The top and bottom 25% are ignored, which removes the influence of any outlying values It is inaccurate if there are large intervals between the scores It is less meaningful if data aren’t normally distributed Easy to calculate, more so than the s.d. Exam hint: You may be presented with data and then asked which measure of central tendency/dispersion to use and have to justify your choice. Justify means give reasons for, not describe what it is. So, look at the type of data (is it category-based or not), are there any extreme values? and does the calculation need to be quick and easy?