Statistical Tests: How to Choose a Statistical Test: Consolidation Page 1/3
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Q1. If we wished to test whether there was any association between Gender and uptake of Flu vaccination which would be the best test to choose?
The answer is c). Both variables are categorical so the Chi square test is used.
Q2. If we wished to test if there was a difference between the gestational age of babies at birth and the use of a nutritional supplement by their mothers during pregnancy which would be the best test to choose?
The answer is d). We have two independent groups defined by a categorical and a continuous variable. The decision to be made is whether the continuous variable is Normally distributed. Gestational age is likely to be negatively skewed because pregnancies rarely go beyond 42 weeks. So a non-parametric test is required for independent samples which is the Mann-Whitney U. If the data followed a Normal distribution or could be transformed to follow one then an Independent Samples t-test could be used.
Q3. The cotinine level was measured in women at the beginning and end of their pregnancy. The change in cotinine was presented on a Log scale. Which would be the best test to use to see if there had been a change in cotinine level during pregnancy?
The answer is g). We have paired observations from the same subject taken on different occasions. When data is presented on a Log scale it is usually because the transformation results in the data following a Normal distribution, so a parametric test can be used. In this case the Paired Samples t-test. A Mann-Whitney U test would be used when the data does not follow a Normal distribution.
Q4. If we wished to estimate the strength of the linear relationship between the weight of a mother and the weight of her baby at birth which would be the best test to choose?
The answer is b). Pearson Correlation estimates the strength of a linear relationship. Linear Regression estimates the nature of the relationship and assumes that one of the variables, the independent variable can be used to predict the nature of the dependent or outcome variable. If the relationship was not linear then Spearman Rank Correlation could be used.
Q5. The pre-operative and post-operative anxiety levels of adolescent patients undergoing orthopaedic surgery were measured using the State-Trait Anxiety Inventory STAI scale. The authors reported the pre-operative anxiety levels as mean = 33.8 (SD = 5.1) and post-operative anxiety levels as mean = 38.8 (SD = 7.2). Which would have been the most appropriate test to assess the relationship between pre and post operative anxiety?
The answer is g). We have paired data from the same subjects so a Paired Samples t-test is appropriate assuming the differences in the data followed a Normal distribution which is implied by the presentation of the means and standard deviations. The authors of this study did not present the mean difference of the pre - post values which should be quoted together with 95% confidence intervals.
Q6. Which test would you choose to compare two groups with skewed unpaired continuous data?
The answer is d.
Q7. Which test would you choose to compare the relationship between two continuous variables which had skewed distributions?
The answer is a). The Spearman Rank Correlation coefficient is used. Pearson correlation assumes that at least one of the variables follows a Normal distribution.
Q8. Which test would you choose to compare a single sample of non-parametric values with a published value?
The answer is e). You would use the Wilcoxon Signed-Ranks test to compare the data values from your sample with the published value where the data does not follow a Normal distribution. You pair each sample value with the published value. If the data was Normally distributed you could use the one sample t-test.
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