Statistical Tests

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  • Created by: cleomos
  • Created on: 05-06-18 11:08

t-test

  • Compares means & standard deviation of 2 data sets
  • If more than 30 samples per data set then infinity degrees of freedom
  • If less than 30 samples per data set then use n1 + n2 - 2 (n = number of samples in data set)
  • Null hypothesis is "No significant difference between sets of data"
  • If t > critical value then reject the null hypthesis, there is a signifcant difference

Standard Deviation:

  • Square root of variance
  • Variance: work out mean, subtract mean from each result and square the difference, average all square differences
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Spearman Rank Correlation

  • Looks for correlation or relationship
  • Null hypothesis is "No significant correlation between variables x and y"
  • If calculated value (rs) is bigger or equal to the critical value then reject null hypothesis as there is a significant correlation between the variables
  • Positive rs value indicates positive correlation, negative value indicates negative correlation
  • Values of rs are between -1 and 1
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Chi-Squared Test

  • Used to compare observed and expected values
  • Can only be used on categorical data e.g. genetic ratios
  • Null hypothesis is "There is no significant difference between the observed and the expected values"
  • The number of degrees of freedom is found by using the number of categories minus one
  • If the calculated value of chi squared is greater than or equal to the critical value then reject the null hypothesis as there is a significant difference between the observed and expected
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Lincoln Index

Used to estimate population numbers:

Number marked in 2nd sample ÷ total caught in 2nd sample = 

Number marked in 1st sample ÷ size of whole population (n)

Assume:

  • No immigration
  • No emigrations
  • No births/deaths
  • Random mixing
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Simpson's Diversity Index

Measures species richness

High value of D indicates stable and species rich environment

Low value of D indicates agricultural management

n = number of species

N = total of species

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