Year 2 Brainscape Qs Flashcards
What is the formula for standard deviation? [1]
Square root of an average of all the individual points’ (distances from the mean)2
What measures of location and spread are used in a data contained in normal distribution? [2]
Mean and standard deviation
What measures of location and spread are used in the presence of outliers in the data? [2]
Median and interquartile range [2]
What change in standard deviation flattens the curve and what makes it taller and thinner? [2]
Flat: Increased SD
Tall and thin: Decreased SD
How many standard deviations from the mean
(+ and -) is 90%, 95% and 99% of population contained? [3]
90%:1.64 SD
95%: 1.96 SD
99%: 2.58 SD
How is standard error calculated and when is it used? [2]
SE = Standard deviation / sq root (sample size)
It is used as a standard deviation of the distribution of all possible sample means (used when dealing with sampling from the population)
How is confidence interval calculated? What does 95% CI = 21.4 to 22.6 mean BMI? [2]
95% CI = sample mean =/- 1.96 x standard error
It means that we are 95% sure that in the population the mean BMI can be as low as 21.4 and as high as 22.6.
What happens to CI if the sample size is increased? [1]
The confidence interval gets narrower
Which variable in the linear regression equation indicates outcome and which is the predictor? [2]
Y – outcome
X – predictor
What test is used to establish p-value while comparing two means? [1]
Two sample t-test
What are different types of clinical trials? [3]
Uncontrolled – everyone gets treatment
Controlled – treated group (‘new treatment’) vs untreated group (placebo or ‘standard treatment’)
Randomized controlled – allocation to groups is determined by chance
What are the types of blinding? [2]
Single blind: patients don’t know what treatment they’re getting
Double blind: both patients and observers (examining doctors) don’t know what treatment each patient is getting
What type of randomized controlled trail is used if the treatment is irreversible and which if it’s reversible? [2]
Irreversible: parallel group
Reversible: crossover
Name two disadvantages of crossover design? [2]
How can we compensate for one of them? [1]
Time consuming
Carry-over effects: washout period before second treatment
What is the difference between intention-to-treat and on-treatment analyses? [2]
Which one is better and why? [2]
TT: compare all subjects in treatment group regardless of whether they complied and acc took the drug
OT: compare subjects who acc took the treatment
ITT is better as it is a better representation of what would happen in real life
When is relative risk statistically significant? [1]
When 95% CI for that relative risk excludes 1
What would be the relative risk if the treatment didn’t have any effect?
RR = 1
What is the type of diagram used in meta-analyses? [1]
Forest plot
What diagram is used to assess publication bias of meta-analyses?
Funnel plot
Give overview of a design of cohort studies? [3]
What is the main question of cohort studies? [1]
Identify cohort
Measure exposure
Follow up over time to identify whether they have disease or not
Is the disease more common in exposed or unexposed?
What are the sources of bias in the cohort studies? [2]
Loss (of people) to follow-up
Measurement of exposure at only one point in time (it can change very rapidly); selection of cohort
How is relative risk measured in cohort studies? [1]
Incident of disease in exposed population / incidence of disease in unexposed population
What curve is used in survival analyses? [1]
What information does it provide? [1]
Kaplan-Meier curve; shows the proportion of people surviving over time