Statistical Tests + Maths in biology

What is the standard deviation?

• A measure of how spread out all your repeats are from the mean.

What are the advantages of using the SD instead of the range?

• SD shows the spread of data around the mean whereas the range only shows the difference between the highest and lowest values.

• SD reduces the effect of anomalies, whereas the range includes it.

• SD can be used to indicate whether a difference between results is significant.

Why would the standard deviation be more useful for a conclusion?

• No overlap indicates that it is likely to be a significant difference (can’t be 95% confidence without the use of statistics).

• If there is an overlap, that indicates that there is likely not to be a significant difference between these means.

How to decide which stats test should be used?

Chi squared

• Justify choice of hypothesis

• Write a null hypothesis

• Write a conclusion

Formula for Chi-squared

What is the p value?

• 0.05

• Refers to the less than 5% probability that the results are due to chance.

How to calculate degrees of freedom?

• n-1

• n is number of categories

• look at critical value associated with this and see if calculated value exceeds this.

• If it does then there is less than 5% probability that the differences are due to chance → reject null hypothesis.

• If not, then there is more than 95% probability that differences are due to chance → accept null hypothesis.

Student T test

• Justify a choice of statistic: Compare 2 mean averages

• Write a conclusion: less than 0.05= likely to not be due to chance as it shows significant change.

Interpret information risk factors and lung disease

What’s the point of a dilution?

• Enables you to make solutions with very low concentrations, without having to measure out very small volumes, this improves accuracy.

Dilution series calculation

Standard Deviation Question

Correlation coefficient Question

T-test Question

P values question

Another standard deviation question

Why are logarithms/log scales used?

• To help compare values that have a large range- comparing very small values to very large.

• Calculate log 10s

• 10 to power of log for opposite

How to reduce uncertainty?

• Multiple instances of measurement e.g. pile 10 leaves on top of each other and divide by 10 rather than doing 10 times. Divides uncertainty by 10.

Uncertainty=

Range/2

Percentage uncertainty