Statistical Skills Statistic Description Example Type Data,: 3, 4, 4, 4, 6, 6, 9 The mean ( ) is what you know as the x average, and you find it by adding Mean together all the values : 3 + 4 + 4 + 6 + 6 + 9 = 36 = 5.1 x consideration and dividing the total by 7 7 the number of values. The mode is simply the most frequently occurring event. If we are using simple Data: 3, 4, 4, 4, 6, 9 Mode numbers, the mode is the most frequently occurring number. If we are Mode (most frequently occurring looking at data on the nominal scale number) = 4 (grouped into categories), the mode is the most common category The median is the central value in a Data: 3, 4, 4, 4, 6, 9 Median series of ranked values. If there is an Median (central value) = 4 even number of values, the median is the mid-point between the two Data: 3, 4, 4, 6, 6, 9 centrally placed values. Median = 5 The interquartitle range is a measure Monthly average temperatures of the spread of values around their median. The greater the spread the higher the interquartile range. Stage 1 Place the variables in rank order, smallest largest last. Interquartile 2 range Find the upper quartile. This is found Ranked: by taking the 25% highest values and 4 5 5 7 7 9 11 12 15 15 17 17 finding the mid between the l l lower highest of these and the next highest upper value. quartile quartile Stage 3 6 15 Find the lower quartile. This is obtained by taking the 25% lowest Interquartile Range: (15 – 6) = 9 values and finding the mid-point between the highest of these and the next highest value. 4 Find the difference between the upper and lower quartiles. This is the interquartile range, a crude index of the spread of values around the median
Statistical Skills Statistic Type Description Example Mean The mean ( x ) is what you know as the average, and you find it by adding together all the values consideration and dividing the total by the number of values. Data,: 3, 4, 4, 4, 6, 6, 9 x : 3 + 4 + 4 + 6 + 6 + 9 = 36 = 5.1 7 7 Mode The mode is simply the most frequently occurring event. If we are using simple numbers, the mode is the most frequently occurring number. If we are looking at data on the nominal scale (grouped into categories), the mode is the most common category Data: 3, 4, 4, 4, 6, 9 Mode (most frequently occurring number) = 4 Median The median is the central value in a series of ranked values. If there is an even number of values, the median is the mid-point between the two centrally placed values. Data: 3, 4, 4, 4, 6, 9 Median (central value) = 4 Data: 3, 4, 4, 6, 6, 9 Median = 5 Interquartile range The interquartitle range is a measure of the spread of values around their median. The greater the spread the higher the interquartile range. Stage 1 Place the variables in rank order, smallest largest last. 2 Find the upper quartile. This is found by taking the 25% highest values and finding the mid between the highest of these and the next highest value. Stage 3 Find the lower quartile. This is obtained by taking the 25% lowest values and finding the mid-point between the highest of these and the next highest value. 4 Find the difference between the upper and lower quartiles. This is the interquartile range, a crude index of the spread of values around the median Monthly average temperatures Ranked: 4 5 5 7 7 9 11 12 15 15 17 17 l l lower upper quartile quartile 6 15 Interquartile Range: (15 – 6) = 9
Skills-and-definitions-AS-Revision.docx