Statistical tests

How is the standard deviation better than the mean?

It uses all the observations, and it is less affected by outliers

What does a low standard deviation show?

Most values remain close to the average, small standard deviation

What does a high standard deviation show?

There is a wider spread of values about the mean, standard deviation is large

What happens if standard deviations of different data sets overlap?

The 2 sets of results are not significantly different

What happens if there is no overlap?

2 sets of results are significantly different

When do you use standard deviation?

It is useful when comparing consistency between different data sets

What does chi squared look at?

Frequencies obtained compared with the frequencies expected to get, in order to determine whether the difference is significant or not

What is the null hypothesis always as?

There is no significant difference between the observed and expected frequencies

What does it mean if x2 is small?

Small difference between the observed and expected data - null hypothesis is accepted

What does it mean if x2 is large?

Huge difference between observed and expected data. Null hypothesis is rejected

What is spearman’s rank used for?

Assesses the degree of association between different measurements from the same sample, if you are looking for a positive/negative correlation between 2 variables. Clarifies the confidence in which a correlation exists

What happens if an answer is positive/negative?

Positive/negatively correlated

What do paired t tests measure?

Compares means from the same group at different times

What does an unpaired t test measure?

Compares means of 2 distinct, unrelated groups

What is accuracy?

How close a measured value is to the true or accepted value

What is precision?

How close repeated measurements are to each other (consistency) - standard deviation measures precision

What is repeatability?

When the same person gets similar results using the same method and equipment

What is reproducibility?

When different people or labs get similar results using the same method

What is uncertainty?

The range within which the true value is expected to lie (often ± value)