Epidemiology/Statistics Flashcards
What are parametric tests?
Parametric tests assume a normal distribution of population data for the variable being tested and are used for testing variables within a population that are interval or ratio.
examples:
Pearson
t-tests
Analysis of variance (ANOVA)
f-test
z-test
What are non-parametric tests?
Non-Parametric tests can be used for data that is not normally distributed within a population or is of nominal or ordinal value.
Examples:
Chi-squared
Spearman
Mann Whitney
Wilcoxin Signed Rank
Fisher Exact Probability
Categorical/Nominal variable
mutually exclusive, but not ordered, categories (e.g. eye color)
Ordinal variable
order matters but not the difference between values (e.g. pain score)
Interval variable
difference between two values is meaningful. The difference between a temperature of 100 degrees and 90 degrees is the same difference as between 90 degrees and 80 degrees (e.g. temperature)
Ratio variable
has all the properties of an interval variable, but also has a clear definition of 0.0. When the variable equals 0.0, there is none of that variable (e.g. height/weight)
What are tests of correlation?
Pearson (parametric)
Spearman (non-parametric)
What is sensitivity?
Sensitivity is the ability of a test to correctly identify disease.
Calculation: true positives / number of people with disease
What is specificity?
Specificity is the ability of a test to correctly exclude a disease
Calculation: true negatives / number of people without disease
What is positive predictive value?
Calculation: True Positives/All positive test results
What is negative predictive value?
Calculation: True negatives / all negative test results
What is positive likelihood ratio?
LR+ = Sensitivity / (1 - Specificity)
If the ratio is more than 10, the test is useful. If the ratio is between 5 and 10, then the test is moderately useful. If the test is less than 1, the test is not useful.
What is negative likelihood ratio?
LR- = (1- Sensitivity) / Specificity
What is the chance of successful delivery with VBAC?
successful VBAC after a single c-section is 72-76%.
If a patient has had a previous successful VBAC the figure is 87-90%
The success rate is lower if any of the following are present:
Induced labour
No previous vaginal birth
Obesity (BMI >30)
Previous C-section for dystocia
What is absolute risk reduction?
ARR = AR in control - AR in experimental
What is relative risk?
Calculation: Probability of an event when exposed/Probability of event in control group
what is relative risk reduction?
Calculations: 1 - RR
What is the number needed to treat?
Calculation: 1 / Absolute risk reduction
What is the odds ratio?
Calculation: (disease present/disease absent in exposed group) / (disease present / disease absent in control group)
What do the OR/RR/HR values mean?
- If the RR, OR, or HR = 1, or the confidence interval (CI) = 1, then there is no statistically significant difference between treatment and control groups.
- If the RR/OR/HR >1, and the CI does not include 1, events are significantly more likely in the treatment than the control group.
- If the RR/OR/HR <1, and the CI does not include 1, events are significantly less likely in the treatment than the control group.
When is the ovarian cancer peak prevalence and incidence?
Peak prevalence = 60-69
Peak incidence = 80+
What is RCT most appropriate to investigate?
Intervention/treatment
What is cross-sectional study most appropriate to investigate?
Diagnostic tests
What is a cohort study most appropriate to investigate?
Assessing prognosis
How do you calculate confidence intervals?
Calculation of 95% CI for mean = (mean - 1.96xSEM) to (mean + 1.96xSEM)
What is the miscarriage rate of women >45?
93%
What is the miscarriage rate of women 40-44?
51%
What is the miscarriage rate of women aged 35-39?
25%
What is the miscarriage rate of women aged 30-34?
15%
The World Health Organisation (WHO) define maternal death as
maternal death to have occurred during pregnancy or within 42 days of termination of pregnancy.
What are the levels of evidence?
Ia - Evidence from Meta-analysis of Randomized Controlled Trials
Ib - Evidence from at least one Randomized Controlled Trial
IIa - Evidence from at least one well designed controlled trial which is not randomized
IIb - Evidence from at least one well designed experimental trial
III - Evidence from case, correlation, and comparative studies.
IV - Evidence from a panel of experts
What factors decrease risk of ovarian cancer?
Oral contraceptive use
Higher Parity
Breast feeding
Hysterectomy
Tubal Ligation
Statins
SLE
Where do most ectopic pregnancies occur?
Ampullary section 70-80%
Isthmus 12%
Fimbrial 5-11%
Cornual and interstitial part of the tube 2%
What percentage of ectopics are non-tubal?
3-5%
What is the additional risk of perinatal death with VBAC?
2-3/10,000 additional risk of birth-related perinatal death
The World Health Organisation define the maternal mortality ratio as
The maternal mortality ratio is the number of maternal deaths per 100,000 live births.
What is the maternal mortality rate associated with ectopic pregnancy in the UK?
0.2%
Which of infection is most commonly associated with an increased risk of ectopic pregnancy?
Neisseria Gonorrhoea
What is the risk of the infant developing hypoxic ischaemic encephalopathy with VBAC?
8/10,000
What happens when a study’s sample size is increased?
Increasing sample size decreases type 2 errors and increases power of the results.
Sensitivity and specificity of the test should remain constant regardless of sample size.
What is the additional risk the baby will have respiratory problems after VBAC compared to elective repeat C-section (ERCS)?
Risk 1-2% greater with ELCS.
What is the commonest prevalence and incidence for endometrial cancer?
Incidence is highest at 70-74 years of age; while prevalence is highest at 60-64.
You are carrying out analysis of a new test for DVTs and decide to plot a ROC curve. What are the axes of the curve?
Sensitivity vs 1-Specificity
What is the risk of uterine rupture after C-section?
25/10,000 or 0.2-0.8%
or 2-8/1000
what condition increases risk of endometrial cancer?
PCOS
WHO defines the perinatal mortality rate as
The number of stillbirths and deaths in the first week of life per 1000 births
What test can be used with a continuous variable?
Mann-Whitney U test
Squamous cell carcinoma accounts for approximately how many cases of vulval cancer?
90%
What are the steps in an audit cycle?
- selection of a topic
- identification of an appropriate standard
- data collection to assess performance against the pre-specified standard
- implementation of changes to improve care if necessary
- data collection for a second, or subsequent, time to determine whether care has improved.
A woman has a routine cervical smear and the results show low-grade abnormality. The HPV test is positive, so she is referred for a colposcopy.
What is the chance of her being diagnosed with cervical cancer with this smear result?
1 in 1000.
What is the approximate chance of a pregnant woman in the UK experiencing a stillbirth?
1 in 200
What is the action of Tranexamic Acid?
Anti-fibrinolytic
Most common inherited bleeding disorder?
von Willebrand disease
Patient homozygous for HbSS - condition called?
Sickle cell disease
A chromosome where the centromere is not central and is instead located near the end of the chromosome?
Afrocentric chromosomes
Atosiban is:
Oxytocin antagonist
