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Part 1 MRCOG > Research tools > Flashcards

Research tools Flashcards

1
Q

What is the standard error of the mean/ how to calculate?

A

Measures how much discrepancy is likely in a sample’s mean compared with the population mean

Standard deviation divided by square root of sample size

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2
Q

How do you calculate the chance of making a type 2 error/ what is a type 2 error?

A

Type 2 error = beta (failing to reject the null hypothesis when it is actually false i.e. false negative rate)

Sensitivity = power.
The higher the power/ sensitivity, the lower the chance of a type 2 error

1-power/sensitivity = P(type II error)/ beta
Power/ sensitivity = 1-P(type II error)/ beta

Incorrect acceptance of a null hypothesis

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3
Q

What is a type I error and how is it calculated?

A

Type I error = false positive rate
alpha (type I error) = 1- specificity

Incorrect rejection of a true null hypothesis

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4
Q

How to calculate true positive rate (TPR)

A

TRP = sensitivity = Power = 1- beta (FNR/ type II error)

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5
Q

How to calculate true negative rate (TNR)

A

TNR = specificity = 1-alpha (FPR/ type I error)

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6
Q

What is number needed to treat and how is it calculated?

A

Measure of effectiveness of an intervention: the number of subjects needed to receive an intervention for one event to be prevented/ occur

NNT= 1/AR

AR= absolute risk
AR = risk observed group - risk control group

Risk for each group= number of events occurring in that group divided by the total population.

The lower the NNT, the more effective the intervention.

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7
Q

Odds ratio

A

Odds of an event occurring in one group divided by the odds of it occurring in the other group

OR= odds observed groups/ odds control group (a/b)/(c/d)

a- number of subjects with event occurring in observed group
b- number of subjects without event occurring in observed group
c- number of subjects with event occurring in control group
d- number of subjects without event occurring in the control group

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8
Q

What is an ROC curve and what is on the axes?

A

Receiver operating characteristic curve: illustrates the performance of a binary classifier model at varying threshold values.

X axis: False positive rate (1-specificity)

Y axis: True positive rate (sensitivity)

The larger the area under the curve, the more accurate the test

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9
Q

Negative predictive value calculation

A

TN/ (TN+FN)

TN= true negative
FN = false negative

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10
Q

Term for condition in which statistical difference occurs purely by chance

A

Type 1 error

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11
Q

Relative risk calculation

Odd’s ratio calculation

A

Relative risk is the ratio of risk in an exposed group compared to a non-exposed group

RR = probability of an event when exposed/ probability of even in control group

Exposed & disease = a
Exposed & no disease = b
Control & disease = c
Control & no disease = d

RR = [a/(a+b)]/ [c/(c+d)]
OR = [a/b]/[c/d]

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12
Q

Incidence of ovarian cancer in UK

A

22 per 100,000

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13
Q

Risks associated with VBAC and statistics

A

2-3/10,000 additional risk of birth related perinatal death

8 in 10000 infant developing hypoxic ischaemic encephalopathy

22-74 in 10,000 risk of uterine rupture

1% additional risk of either blood transfusion or endometritis

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14
Q

Difference in risk of baby having breathing problems in VBAC vs repeat ELCS?

A

VBAC reduces the risk

Rates are 2-3% with VBAC compared to 3-4% with ELCS

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15
Q

Parametric vs non-parametric statistical tests

A

Parametric assume a normal distribution of population data. For example:
- Pearson (correlation test)
- T-test
- Analysis of variance (ANOVA)
- f-test
- z-test

Non-parametric can be used for populations that aren’t normally distributed.
For example:
- Spearman (correlation test)
- Mann Whitney
- Chi-squared
- Wilcoxon Signed Rank
- Fisher Exact Probability
- Kruskal Wallis
- Friedman

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16
Q

Levels of evidence

A

Ia- Evidence from meta-analysis of RCT

Ib- Evidence from at least one RCT

IIa- Evidence from at least one well designed controlled trial (not-randomised)

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

17
Q

Risk factors vs protective factors for ovarian ca.

A

Risk:
- Age, obesity, FHx, HRT (oestrogen only)

Protective:
- OCP, higher parity, breast feeding, hysterectomy, tubal ligation, statins, SLE

18
Q

What is the success rate of VBAC following 1x CS

How does this change if she has had 1x successful VBAC

What lowers the success rate?

A

72-76%

87-90%

Induced labour
No previous vaginal birth
Obesity (BMI>30)
Previous CS for dystocia

19
Q

What type of study is the most appropriate to assess treatment/ intervention, diagnostic test and prognosis

A

Treatment/ intervention: RCT

Diagnostic tests: cross sectional study or analysis

Assessing prognosis: Cohort study

20
Q

Average age of diagnosis of uterine cancer in the UK

A

Age 60

Most cases seen in age 60-64

Incidence rate (cases per 100,000) is highest in the 70-74 age group

21
Q

WHO definition of maternal death

A

Death of a woman whilst pregnant or within 42 days of termination of pregnancy

22
Q

Miscarriage rates in relation to age at conception

A

20-24, 9%
25-29, 11%
30-34, 15%
35-39, 25%
40-44, 51%
>45, 93%

23
Q

Maternal mortality rate of ectopic pregnancy in UK

A

2 per 1000 (0.2%)

24
Q

WHO definition of perinatal mortality rate

A

Number of stillbirths and deaths in first week of life per 1000 births

25
Q

Peak incidence for ovarian ca. vs decade with most cases

A

80-84 age group (number per 100,000)

60-69 age group comprises the most cases

26
Q

Increasing sample size decreases what type of errors

A

Type 2

27
Q

WHO definition of maternal mortality ratio

A

Maternal deaths per 100,000 live births

28
Q

Direct vs indirect maternal deaths

Maternal mortality rate (MMBRACE)

A

Direct: those resulting from obstetric complications of pregnancy e.g. VTE

Indirect: deaths resulting from pre-existing disease or disease that developed during pregnancy which was not due to direct obstetric causes, but was aggravated by physiologic effect of pregnancy

Maternal mortality rate: deaths during pregnancy or within first 42 days following end of pregnancy per 100,000 maternities (for any cause related to or aggravated by pregnancy- not including accidental or incidental causes)

ICD-10 includes late maternal deaths occurring between 6 weeks and 1 year after childbirth.

29
Q

Types of data

A
  1. Categorical
  • Nominal: names or categories with no order e.g. eye colour, sex, ethnic group
  • Ordinal: there is ranking within the categories, but not on a scale e.g. APGAR scores
  1. Quantitative
  • Interval: there is ranking of the numbers, but on a scale and values are equally spaced e.g. temperature
  • Ratio: as for interval, but 0 means the variable is absent e.g. length
30
Q

Parametric vs non-parametric statistical tests

A

Parametric= for normally distributed samples
EXAMPLES

  • T-test: independent when comparing 2 unpaired distributions or paired when comparing 2 paired distributions
  • ANOVA (analysis of variance): used when multiple distributions are compared. Also assumes spread of each distribution is the same

Non-parametric = for samples that aren’t normally distributed

  • Mann Whitney U test (equivalent of independent t-test)
  • Wilcoxon’s signed rank test (equivalent of paired t test)
  • Kristal-Wallis one way analysis of variance (equivalent of ANOVA)
  • Friedman two way ANOVA
  • Chi squared (for categorical data)
31
Q

How to calculate variance

A

The average of the squared differences from the mean
(v. long equation)

32
Q

How to calculate standard deviation

A

square root of variance

33
Q

Objectives of phase 0 to IV clinical trials

A

Phase 0: pharmacokinetics: oral availability and half life

Phase I: dose-ranging on healthy volunteers

Phase II: efficacy and side effects

Phase III: Assess efficacy, effectiveness and safety

Phase IV: Post marketing surveillance in public

34
Q

Positive/ negative likelihood ratios that indicate a moderately useful clinical test

A

PLR: 5-10 (higher the value, the better)

NLR: 0.1-0.2 (lower the better)

Part 1 MRCOG (13 decks)

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