Statistics Flashcards
What indicates if a test is reliable?
If it is repeated again and again and gets the same result
What does it mean if a test is valid?
If it meets the requirements of the scientific study
e.g. randomisation, blinding
What type of data is nominal?
categorical, with no ranking
e.g. gender, blood group
What type of data is ordinal?
categorical with ranking
e.g. preference scale
what type of data is discrete?
numerical data which is in whole numbers
e.g. number of people
What is the variance of a sample? How is it calculated?
A measure of dispersion of sample
Average of squared differences from the mean
What is the relationship between variance and SD?
SD = square root of variance
What assumptions must be made with parametric data?
Continuous data
Population data is normally distributed
Sample and source population have same SD/variance e.g. spread
When are non-parametric tests more appropriate than parametric?
When data is not continuous (e.g. ordinal, nominal)
When distribution of population is not known
Small sample size -> less affected by outliers, uses median rather than mean. RANKS data
What is the central limit theorem?
In a skewed population, sample becomes more “normal” in shape as n increases
What is the parametric test used to compare 2 independant groups?
What is the non-parametric equivalent?
T-test
Wilcoxon rank sum test
What is the parametric test used to compare paired observations?
What is the non-parametric equivalent?
T-test for paired
Wilcoxon signed rank test
What is the parametric test used to compare several groups?
What is the non-parametric equivalent?
ANOVA
Kruskal Wallis test
What is the parametric test used to find linear relationship between 2 variables e.g. BP and sleep duration?
What is the non-parametric equivalent?
Pearson’s correlation
Spearman’s Rank correlation
What is the non-parametric test used to test association between 2 qualitative variables e.g. gender, smoking status?
Which one for sample size
>50?
<50?
Chi squared
> 50 -> chi squared
<50 -> Fisher’s exact
What is the difference between t-statistic and z-statistic?
T = sample with unknown SD
Z = known SD
What is a Type 1 error?
How is it minimised?
False positive
i.e. wrongly rejecting null hypothesis
Avoid by setting p-value low enough
What is a Type 2 error?
How is it minimised?
False negative
i.e. wrongly accepting null hypothesis
Avoid by having enough POWER
What is “power” of a study?
i.e. what does 80% power in a study mean?
The ability of a study to demonstrate a statistically significant association
80% power = study has 80% chance of ending with a p-value <0.05
What is “power” of a study?
i.e. what does 80% power in a study mean?
The ability of a study to demonstrate a statistically significant association
80% power = study has 80% chance of ending with a p-value <0.05
What would changing your p-value cut-off from 0.05 to 0.01 do to the power of a study?
Decrease it
Smaller p-value requires more power
How can power be increased in a study design?
Increase sample size
Increase p-value
Increase effect size
What does a 95% confidence interval indicate?
we are 95% confident that true population mean occurs within this interval
What error is more likely with post-hoc analyses?
Type 1 error
