# Statistical Analysis Biology

- Created by: rosie061
- Created on: 16-09-13 04:24

First 397 words of the document:

1.1 Statistical Analysis

1.1.1 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

1.1.2 Calculate the mean and standard deviation of a set of values

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

1.1.3 State 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

1.1.4 Explain how standard deviation is useful for comparing the means and the

spread of data between two or more samples.

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 (ttest)

1.1.5 Deduce the significance of the difference between two sets of data using

calculated values for t and appropriate tables

Any significant difference between two data sets

Calculate a "pvalue": The probability that there is no difference between the

two samples

High P values: Small differences (high probability there is no significant

differences between results)

P>0.05: There is no significant difference between the two samples

P<0.05: There is a significant difference between the results

Converting a ttest result (tvalue) to a pvalue:

"Table of tValues" Pg. 7 of textbook

1. Work out the nos of degrees of freedom (DF)

o DF=total nos. of results 2

o E.g. Sample 1 (9,5,4,3,2) Sample 2 (6,9,12,14,5): DF=102=8

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