Stats Flashcards
Graphical methods of presentation(x5)
- scatter plot
- bar chart
- histogram
- mean +/- s/d
- box plot
When would the median and mode be different to the mean value?
Small samples and skewed distributions (non-normal)
When can the t-test be employed?
When the data (raw/transformed) follow a normal distribution
Response if P
Difference is significant – reject null hypothesis
Response if P>critical value
Cannot reject null hypothesis
Box and whisker plot: what are the values represented within the box?
Values between the 25th and 75th percentile
Box and whisker plot: what do the whiskers represent?
Whiskers show the range of data
What is the type I error?
False positive result; rejection of the null hypothesis when it is true
In what instances is it likely to cause a type I error?
Rejection of null hypothesis when p-value is close to 0.05
What is type II error?
Not rejecting the null hypothesis when it is false; might erroneously conclude that no effect is present when there actually is
Factors affecting the power of a stats test (x4)
- sample size
- variability of observations
- effect of interest
- significance level desired
Which test is used to avoid the problem of multiple corrections?
Global test - ANOVA (analysis of variance)
What do you do if the ANOVA test yields a significant result (ie if P
Move to other tests e.g. Post-hoc tests - bonferroni, scheffe
When is non-parametric stats used? (X2)
- when normality cannot be assumed
- categorical data
How is the Mann Whitney test used?
The individual data scores are converted into ranks for any subsequent analysis
What is the non-parametric alternative to the paired t test
Wilcoxon signed rank test
What is the global test used in non-parametric stats?
Kruskal-Wallis
What is the correlation analysis?
The degree of association between two variables
How is data presented in correlation analysis?
Scatter plot
What’s on the x and y-axis of the scatter plot?
X-axis: independent variable
Y-axis: dependent variable
What does pearson’s correlation coefficient measure?
The degree of linear association between two variables
Range of values of the pearson’s correlation coefficient
-1 to +1 (sign indicates the direction of association)
In what cases will Pearson’s ‘r’ value be misleading? (X3)
- non-linear r/s
- presence of outliers
- presence of subgroups
When do you not use pearson’s? (X3)
- if one variable is on the ordinal scale
- if x or y are not normally distributed
- if the sample size is too small
What should be used in cases when pearson’s correlation coefficient is not used?
Spearman’s rank of correlation
What is the coefficient of determination?
It determines how well the regression line accounts for variability in the dependant variable
Ways of presenting data (x2)
Table
Graph
