·

Error bars

State that error bars are a **graphical representation of the variability** of data

- Bars on a graph extending
**above and below the mean value**showing the variability of the data. - Can represent the range of data/standard deviation
**Larger error bars**: less reliable data**Smaller error bars**: more reliable data

Mean and Standard deviation

Calculate the mean and standard deviation of a set of values

In IB Biology curriculum, there are **three types of average:**

**Median:**the middle value of a range of results**Mode:**the value that appears the greatest nos. of times**Mean:**the sum of all the results divided by the nos. of results

If the mean, mode and median are approximately the same we can usually assume that the data shows a ‘

**normal distribution**’: Bell shaped frequency**Standard deviation:**

- Calculator: Menu (2:Stat), List, F2, F1(1VAR), sx(standard deviation)
- Excel

In IB Biology, it is common that the term standard deviation is used to summarize the spread of values around the mean and that **68%** of the values fall within one standard deviation of the mean

Explain how standard deviation is useful for comparing the means and the spread of data between two or more samples.

There are four key points about standard deviation in IB Biology curriculum:

**Small standard deviation**: data is clustered around the mean value, a more reliable mean value**Large standard deviation**: Date is more spread out, mean is less reliable- Can be used to say whether a particular result lies outside the
**normal range of data** - Can’t be used to compare two different samples (t-test)

End of the topic!

Drafted by Gina (Biology)