The standard deviation is 9, but we divide by 1 when comparing means. What changed?

Standard deviation and standard error may look like the same type of 'variability,' but they refer to different things. If ...
TES

A-level Biology Statistics and Maths Skills: AQA-style workbook, practice papers and lessons

A-level Biology Statistics and Maths Skills Complete Pack (AQA and OCR): 162 questions, 2 practice papers and 9 PowerPoint lessons. Standard deviation and error bars ...