Mean, standard deviation & error bars
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Question
What is the formula for the mean?
Answer
$\bar{x} = \dfrac{\sum x}{n}$ — **add all the values and divide by how many there are** ($n$). The mean keeps the same units as the data.
Question
Mean vs median vs mode?
Answer
**Mean** = add-up-and-divide average. **Median** = the **middle** value in order. **Mode** = the **most common** value (tallest bar on a frequency graph).
Question
What does standard deviation (s) measure?
Answer
How **spread out** the data are around the mean. **Small s** = tightly clustered; **large s** = widely scattered. You find it on your GDC, not by hand.
Question
What does an error bar represent?
Answer
The **spread** of the data — usually **± one standard deviation** about the mean. Its total height = 2s; a longer bar means more spread (less reliable).
Question
State the overlap rule for error bars.
Answer
Error bars **OVERLAP → difference NOT significant**. Error bars with a **clear gap (no overlap) → difference IS significant**.
Question
On a box-and-whisker plot, what are the key features?
Answer
**Median** = line inside the box; **box** = lower quartile (Q1) to upper quartile (Q3) = middle 50%; **whiskers** = min and max; a **separate point** = an **outlier**.
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Topic 5.1 hub
Experimental and data skills
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