# Data Techniques Revision

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Null Hypothesis: This hypothesis states that the relationship is by chance and not by a non-random cause. You use these statistical analysis to prove that actually the relationship is not down to luck.

Spearman's Rank

How?

Formulate a null hypothesis.

Individually rank the values of each variable. 1 = highest value.

Find the difference between the two.

Square the differences and sum the values.

Input into the formula.

Appropriateness:

Appropriate for data with 10-30 values with 2 variables that are believed to be related.

Pros:

Indicates the statistical significance of a result - rules out chance.

Gives numerical value to the strength and direction of a correlation.

Cons:

Does not show if there is a casual link

Too many tied ranks affect the validity of the test.

Mann Whitney-U

How:

Select null hypothesis.

Rank the data sets across the two columns. 1 = lowest value.

Treat as two separate columns. Add ranks in first column to get your R1 value then add ranks in the second column to get your R2 value.

Input into the formula.

Choose the smaller U value of either U1 or U2.

Compare to the critical values table: less than the critical value means you should reject the null hypothesis at 95…