A New View of Statistics 

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Most statistics need either two significant digits (the first two digits), or two decimal places when the number is less than 1.0:
Percentages: 
73%, 7.3%, 0.73% 
Correlations: 
0.97, 0.23, 0.05 
Relative risks or odds ratios: 
12, 2.4, 0.64 
Effect sizes: 
2.6, 0.51, 0.07 
SDs usually need two significant digits. The mean must match the precision of the SD:
23500 ± 1300 (not 23538 ± 1341 etc.)
2350 ± 130
235 ± 13
2.35 ± 0.13
0.235 ± 0.013
The SD in descriptive statistics for height, weight, and age can often be shown with just one significant digit. After all, it doesn't really matter whether your subjects were 67 ± 5 or 67.3 ± 5.4 kg in weight:
height: 178 ± 7 cm
weight: 67 ± 5 kg
age: 23 ± 4 y
Naturally, if weight was an outcome variable, you would need to show two significant figures.
Avoid p values, but if you have to give in to the demands of a journal reviewer or editor who hasn't seen the Light, show no more than two significant digits: p = 0.007, 0.04, 0.35. See later for more about p values and statistical significance.