Question 3: Find the minimum, maximum, median, first and third quartiles, and the 5th, 10th, 90th, and 95th centiles. Report these to two decimal places.
We can do this using Descriptive statistics, Frequencies. Note that SPSS uses the term 'Percentiles' rather than 'centiles'. If you click Percentiles, type the number in the box, then click Add, SPSS will include each centile you add into the output.
Here is the SPSS output:
Statistics
Triglyceride
N 
Valid 
282 
Missing 
0 

Minimum 
.15 

Maximum 
1.66 

Percentiles 
5 
.2700 
10 
.2900 

25 
.3500 

50 
.4600 

75 
.6000 

90 
.7940 

95 
.9395 
We must report these to two decimal places.
The minimum = 0.15 mmol/L.
The maximum = 1.66 mmol/L.
The median = 0.46 mmol/L.
The first quartile = 0.35 mmol/L.
The third quartile = 0.60 mmol/L.
The 5th centile = 0.27 mmol/L.
The 10th centile = 0.29 mmol/L.
The 90th centile = 0.79 mmol/L.
The 95th centile = 0.94 mmol/L.
For most of these, we had only to remove the zeros in the third and fourth decimal places. For the 90th centile, 0.7940, we have to round the number. If the digit to be removed is 0, 1, 2, 3, or 4, we round down and leave the last digit to remain untouched. If the digit to be removed is 5, 6, 7, 8, or 9, we round up and increase the last digit to remain by one. Here the digit to be removed is 4, so we round down to 0.79. We also have to round the number for the 95th centile, 0.9395, The digit to be removed is 9, so we round up to 0.94.
If they exist, we should always include units in reports of analysis. Here the unit in which serum triglyceride is measured is mmol/L.
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Last updated: 17 October, 2006.