Statistics

What is standard deviation?

A measure of how spread out the repeats are from the mean value.

What are the advantages of using standard deviation instead of the range?

• Standard deviation excludes anomalies whereas the range includes anomalies.

• Standard deviation can be used to determine whether a difference in results is statistically significant whereas the range cannot.

• Standard deviation shows the spread of data around the mean whereas the range is only the difference between the highest and lowest value.

True or false? If there is an overlap in standard deviations, the difference between the results is likely to be significant.

False. IF THERE IS NO OVERLAP IN STANDARD DEVIATIONS, THE DIFFERENCE BETWEEN THE RESULTS IS LIKELY TO BE SIGNIFICANT.

What type of data is correlation coefficient used for?

Continuous data.

When is the correlation coefficient statistical test used?

When there are two continuous variables and you are investigating an association between these two measurements (to see if there is a significant correlation between them or not).

What is the null hypothesis when working with the correlation coefficient?

There is no significant correlation between the two variables.

What does 0 mean in a Spearman’s rank correlation coefficient?

There is no correlation.

What does -1 mean in a Spearman’s rank correlation coefficient?

There is a perfect negative correlation.

What does +1 mean in a Spearman’s rank correlation coefficient?

There is a perfect positive correlation.

How do you work out the difference in ranks (D) when working out the Spearman’s rank correlation coefficient?

Rank one variable from smallest to largest, the the other variable from smallest to largest, calculate the difference between these ranks for each column of variables.

True or false? The Spearman’s rank correlation coefficient has to exceed to critical value for the probability of the correlation being due to chance to be less than 5%.

True.

What type of data is the student t-test involved in?

Continuous data.

What is the student t-test used?

When investigating a difference between two means.

What is the null hypothesis for a student T test?

There is no significant difference between the two means.

What does a paired student T test mean?

Both sets of data were obtained by the same individual, results are paired, both groups have similar sample sizes.

What does an unpaired student T test mean?

The sets of data were obtained by two different individuals.

Give the formula for working out degrees of freedom with a paired student T test.

n - 1

(n = number of samples)

Give the formula for working out degrees of freedom with an unpaired student T test.

(n1 + n2) - 2

True or false? You reject the null hypothesis if the student T test value is lower than the critical value.

False. YOU REJECT THE NULL HYPOTHESIS IF THE STUDENT T TEST VALUE IS GREATER THAN THE CRITICAL VALUE.

What type of data do you used chi-squared tests for?

Frequencies (counting individuals in categories).

When is a chi-squared test used?

When investigating a difference between frequencies (observed and expected results).

What is the null hypothesis for a chi-squared test?

There is no significant difference between the observed and expected results.

True or false? The chi-squared value must be greater than the critical value for the difference to be significant.

True.