STATS EXAMPLE Flashcards
A random selection of 1200 adults agree to participate in a study of the possible effects of drug X.
They are followed prospectively for a period of five years to see if there is an association between the incidence of cataract and the use of drug X.
Which type of study is this?
A Case-control study B Cohort study C Cross-over study D Cross-sectional study E Randomised controlled clinical trial
B Cohort study This is the correct answer
Cohort studies or longitudinal studies involve the follow up of individuals.
A cohort study may be prospective in which individuals who are exposed and non-exposed to a putative risk factor are followed up over a defined period of time and the disease experience of the exposed group at the end of follow up is compared with that of the non-exposed group.
A cohort study may also be historical (retrospective or non-concurrent). A cohort is identified, for whom records of exposure status are available from the past, and whose disease experience can now be measured, a substantial period of time having already elapsed since exposure.
An example of a famous cohort study in medicine is the Framingham study.
• Sensitivity is the ratio of all those truly positive to all those who have the
disease: A/A+C
• Specificity is the ratio of all those truly negative to all those without the
disease D/D+B
• The positive predictive value is the probability that a positive test
indicates presence of disease: A/A+B
• The negative predictive value is the probability that a normal value
indicates absence of disease: D/D+C
• Sensitivity is simply the percentage of sick people who are identified as
having the condition).
• Specificity the percentage of healthy people who are identified as not
having the condition or healthy).
• relative risk (RR) is the risk of an event (or of developing a disease)
relative to exposure.
Relative risk is a ratio of the probability of the event
occurring in the exposed group versus a non-exposed group.
P<0.05 leads to rejection of the null hypothesis – the occurrence is not by chance
Significance allows assumption to be made that effect is real and not by chance
Type I (α): rejects the null hypothesis when the null hypothesis is true
For example telling a man that his urine pregnancy test is positive so he is
pregnant
• Sensitivity is the ratio of all those truly positive to all those who have the
disease: A/A+C
• Specificity is the ratio of all those truly negative to all those without the
disease D/D+B
• The positive predictive value is the probability that a positive test
indicates presence of disease: A/A+B
• The negative predictive value is the probability that a normal value
indicates absence of disease: D/D+C
• Sensitivity is simply the percentage of sick people who are identified as
having the condition).
• Specificity the percentage of healthy people who are identified as not
having the condition or healthy).
• relative risk (RR) is the risk of an event (or of developing a disease)
relative to exposure.
Relative risk is a ratio of the probability of the event
occurring in the exposed group versus a non-exposed group.
P<0.05 leads to rejection of the null hypothesis – the occurrence is not by chance
Significance allows assumption to be made that effect is real and not by chance
Type I (α): rejects the null hypothesis when the null hypothesis is true
For example telling a man that his urine pregnancy test is positive so he is
pregnant
The obstetric team are conducting a study to evaluate whether there has been any effect on patient satisfaction following the establishment of an outpatient IOL programme. Women undergoing inpatient IOL and women undergoing outpatient IOL were asked to rate their overall satisfaction with the process using a visual analogue scale from 1 (least satisfied) to 10 (most satisfied). What is the most appropriate statistical test to assess whether there is a significant difference in satisfaction between the two groups?
Chi squared test Kruskal Wallis test Mann Whitney U test Student’s t test Wilcoxon matched pairs signed rank test
Mann Whitney U test
