Statistics Flashcards
What is the population?
The entire group of individuals is called the population
What is a sample?
A sample is a group selected to represent the population in a research study e.g. population is too large to examine all
What is a variable?
A characteristic that can change or take on different values e.g. height, gender
What are the two main types of data?
Categorical (Qualitative)
Numerical (Quantitative)
What are two types of Qualitative data?
Nominal- no particular order e.g. Hair colour
Ordinal- some order e.g. pain threshold
What are the two main types of Quantitative data?
• Discrete - data that consist of indivisible categories/fixed numbers. e.g., number of
teeth, number of children in a family
• Continuous - infinitely divisible into whatever units a researcher may choose, e.g. weight
What are two types of continuous data?
Interval- no.s with known differences between variables, e.g. time
Ratio- no.s that have measurable intervals where difference can be determined, such as height or weight
What are the 3 measures of central tendency?
Mean
Median
Mode
What are three measures of dispersion?
Range
Interquartile range
Standard deviation
What does the mean represent?
Average or arithmetic mean of the data
What does the median represent?
The middle value when the scores are ranked in order
What does the mode represent?
Most often occurring value
What does the range represent?
Highest to lowest values; this fails to give an indication of the spread of observations about the mean.
What does the Interquartile range represent?
Values that capture the middle 50% of the
distribution. The upper and lower quartiles are the 75th and 25th percentiles.
What does the standard deviation represent?
How closely do values cluster around the mean value in a normally distributed population. It describes the spread of observations on either side of the mean.
What is meant by the standard error of the mean?
The standard deviation of a number of means from different samples of the same population.
This gives an indication of the precision of the sample mean as an estimate of the population mean
What is the difference between the standard deviation and the standard error?
Standard deviation shows how individuals within the sample differ from the mean of the sample.
Standard error is an indication of how far the mean of the sample is likely to be from the actual target population mean.
What are confidence intervals?
A way to indicate the probability that the mean for a population lies within a range of values.
The width of the confidence interval indicates the precision of the estimate.
Why is normal distribution important?
Because parametric statistics assume normal
distributions
How can we tell if a variable is normally distributed?
Distribution unlikely to be normal if:
• Mean is very different from the median
• Two SDs below the mean gives an impossible answer (e.g. height <0 cm)
What is the difference between parametric and non-parametric tests?
Parametric tests assume that data are normally distributed.
Whereas, Non-parametric tests make fewer assumptions about the data.
What is the difference between independent and paired samples?
Independent or unpaired data refers to data from two groups with different members.
Paired samples are samples in which natural or matched couplings occur.
Explain what is meant by the null hypothesis?
When we say the difference in observations between two groups is purely due to chance.
When the results of an investigation are not likely due to chance alone; the null hypothesis may be rejected in favour of the alternative hypothesis.
What is a two-tailed test?
A two-tailed test exists where we do not have a direction of difference between groups for the alternative hypothesis
i.e. the results are different but we cannot say if they are better or worse.
What is a one-tailed test?
Where the alternative hypothesis specifies a direction then a one-tailed test can be used.
E.g. This may be used in an experiment comparing a new treatment to a placebo; we would be expecting the new treatment to perform better.
What is the definition of probability
Calculating the likelihood of an event
happening as a proportion of the number of possibilities (from 0 to 1)
What is the simplified meaning of the p-value?
The p-value tells us how likely it is to get a result like this if the Null Hypothesis is true.
What is clinical significance?
The practical importance of a treatment effect - whether it has a real genuine, palpable, noticeable effect on daily life
What is Statistical significance?
It is used in hypothesis testing, whereby the null hypothesis is tested (that there is no relationship between variables)
Describe the parametric test: student’s t test
It is used for the comparison of two groups of data. It can be used for samples which are either independent (unpaired) or dependent (paired).
Describe the chi-squared test
It is a non-parametric test (for non-normally distributed data) used for either the comparison of a single group to a hypothetical group (paired), two groups of data (unpaired) or more than two groups of data (unpaired)
Describe post hoc tests
They are used to determine where the differences between groups are, following a statistically significant result from ANOVA.
ANOVA can say there is a difference, Post-hoc tests can say where the difference is.
Describe ANOVA tests
ANOVA is used for comparing 3 or more independent sample means.
Describe the importance of randomisation
• Ensures that all the subjects entering the study have an equal chance of being allocated to any group in the study
• Allocation cannot be predicted in advance
• Minimises some types of bias
- controls for confounding factors
• Random sampling is essential for statistical testing (it is assumed for even simple tests)
Give 2 methods of randomisation
Fixed- Methods of allocation and randomisation are determined at the outset of the trial.
Adaptive- Is used to balance characteristics and maintain similarity as a trial progresses
What are 4 methods of fixed randomisation?
Random numbers
Simple randomisation
Block randomisation
Stratified randomisation
