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22 Cards in this Set
- Front
- Back
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What is correlation? |
A measure of linear association between two variables |
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What type of data do you have if you make one observation per individual? |
Independent data |
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What type of data do you have if you make more than one observation per individual, of the same variable? |
Paired data |
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What is a monotonic relationship? |
A positive, non-linear association between two variables |
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How is Pearsons correlation coefficient reported? |
As a value between 1 and - 1 |
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What are the assumptions made when calculating a Pearsons CC? |
- That the two variables are continuous and normally distributed - a linear relationship is present |
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What is a perfect correlation? |
PCC = 1/-1, all data points lie perfectly on line of best fit |
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Write out the formula for PCC |
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What is Cov(X, Y)? |
The covariance of X and Y, a measure of how they change together |
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Write the formula for covariance between X and Y |
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How would you use a table to help calculate a PCC? |
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Why is it always important to graph the data and not just rely on the PCC as a measure of correlation? |
Because many non-linear associations or outliers can influence the PCC to make it appear linear |
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What is a spurious correlation? |
A correlation that seems high but is the result of two unrelated groups that have been combined, each of which have a different correlation |
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Why is a Spearmans Rank Correlation often used in place of a PCC? |
Because it relaxes the assumption of PCC and can be used to show correlations of non-linear data |
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How do you calculate a SRC? |
Rank the data in order from lowest to highest. Then carry out a PCC on the ranks instead of the raw data values |
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What does a p value tell us about the strength of a correlation? |
Nothing - it only tells us whether a correlation is present |
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What else aside from a PCC can be used to estimate correlation? |
A 95CI |
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What is clinical importance? |
The measure of whether a drug produces a large enough effect to be worth using in clinical practice. Is more stringent than statistical significance |
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What is an MCID? |
Minimum clinically important difference |
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What factors influence the value of an MCID? |
The cost effectiveness of a drug, its potential side effects, patient preferences, drug interactions, etc |
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How do you know if a treatment is statistically significant by looking at its 95CI? |
If it crosses 0, it is insignificant |
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How do you know if a treatment is clinically important? |
If its mean difference is above the clinical importance threshold |
