Stats Flashcards
How is SEM calculated?
Standard Deviation /
square root of ‘n’
n = sample size
Calculate relative risk reduction
100 working women and 110 women who are house wives are followed up through pregnancy. 40 working women had LBW babies and 21 house wives had LBW babies.
Draw table
Top: Behaviour: working/housewife
Left side: Outcome: LBW Y/N
(40/100) / (21/110) = 2.1
2.1
CONTRAST odds ratio of LBW
(40/21) / (60/89) = 2.8
What non-parametric tests can be used to test the induction of labour interval between normal and pre eclamptic women? Name 3
Non parametric is for Names or Not normally distributed
Mann Whitney
Wilcox Rank
Spearman
How is the perinatal mortality rate defined?
The number of stillbirths and the number of neonatal deaths within 7 days of life, per 1000 births
ABO blood grouping is?
Parametric/nonparametric
nominal/ordinal
Non-parametric nominal
What is the risk of uterine rupture during a VBAC after 1 CS?
0.5%
or
1 in 200
The diamond shape Forest graph, lateral angles represents:
95% CI
What is the failure rate of vasectomy
0.5/1000
Null hypothesis is ACCEPTED if
i.e. say the variable is without effect
p > 0.05
Statistical analysis used for data with normal distribution. Name 3
Student t
Pearson (P for parametric)
ANOVA
What is the data type of
‘moderate / mild / severe’
Ordinal
What is an alpha or type 1 error
(with regards to the null hypothesis)
False positive
Incorrectly rejecting the null hypothesis
What gestation is defined as stillbirth rather than miscarriage?
24 weeks
Statistical heterogenicity means
Difference between studies
Calculate maternal mortality ratio
Total number of live births 250,000, early neonatal death 1500, Maternal death 750.
Maternal mortality ratio =
(Maternal deaths /live births) X 100,000
(750/250,000) X 100,000 =
0.003 X 100,000 = 300
Calculate SEM
For a group of 10,000
If the Mean 245 and SD 50.
SEM = SD/√n = 50/√10,000 = 50/100 = 0.5
Which study design would describe the relationship between shoulder dystocia and neonatal birth weight ?
retrospective case-controlled study
Calculation for negative predictive value
TN / TN + FN
What is the mode?
The most frequently occurring number (fashionable!)
Grade B recommendation of RCOG means
well controlled studies but non randomized
Incidence of “RARE” disease when translated into mathematics is?
1:1000 or rarer
Calculate BMI
150cm height and 90 kgs weight
BMI = weight / height in metres squared
90kg / 1.5 x 1.5
90/ 2.25 = 40
<18.5 underweight range.
<25, healthy weight range.
<30, overweight range.
Class 1 Obesity <35
Class 2 Obesity <40
*Class 3 Obesity 40 or higher
Calculate perinatal mortality
stillbirths (>=24) and early neonatal (<7/7) deaths per thousand
(BUT question on paper from 2018 and WHO define perinatal period as from 22 weeks?)
What represent the 2 axis of ROC curve ?
Sensitivity (vertical) over
1-specificity (horizontal)
What do the bottom and top represent on the box-and-whisker plot?
Lower and upper quartile
Odds ratio calculation
Del <34/40 (total 209)
Smokers 31
Non-smokers 178
Del >34/40 total 926
Smokers 58
Non-smokers 659
Behaviour: Smoking
Outcome/risk: Del at <34/40/>34/40
(31/178) / (58 / 659)
17.42/8.8 = 1.98
So odds doesn’t ‘use’ the total it’s e.g.
1 in 9 (out of 10 total)
NNT calculation
1 / ARR
Absolute risk reduction
ARR is % risk decrease from one group to another
e.g. drug reduces chance of bad outcome from 50% to 40% then ARR = 10% or 0.1
1 / 0.1 = 10
Pregnancy rate with COCP if perfectly compliant and non perfectly compliant
0.1 / 5-6
VTE with COCP
6 / 10,000
IUD Pregnancy. What is the risk of Ectopic Pregnancy
1/20
The Probability of sarcomatous change occurring in fibroid is
0.1%
Grade A RCOG recommendation means
At least one randomised controlled trial
What type of variable is BMI ?
ordinal / nominal / continuous / categorical / discrete
Continuous
Incidence of uterine rupture in IUCD insertion
1/5000
What is represented by the equation Sensitivity/(1-specificity)?
Positive likelihood ratio
What is the correct formula to calculate specificity?
TN / TN + FP
Calculate PPV
TP / TP+FP
Calculate sensitivity
TP / TP + FN
A study between soya milk and improvement of menopause symptom. the null hypothesis H0 should state that…
There is no relation/difference between soya milk intake and menopause symptoms
WHO defines perinatal mortality as
number of still births after 22 wks & early neonatal deaths per 1000 births
What kind of variable is ‘gestational age’
interval
named, ordered, with proportionate intervals between variables
How do you calculate the type 2 error?
1 - power
e.g. power is 90%
1 - 0.9 = 0.1 or 10%
Risk of expulsion of IUD
~5% (google)
Risk of ectopic pregnancy with IUD
<1 per 1000 years of use
Risk of malignant transformation of leiomyoma into leiomyosarco
0.01%
When a pregnant person is on carbamazepine and lamotrigine, what percent will have foetal congenital anomalies
> 10%
What is the leading cause of maternal death according to MBBRACE
Overall
direct
indirect
Overall - Cardiac
Thrombosis and thromboembolism is the leading direct cause of death during or up to six weeks after end of pregnancy.
You clot because you are pregnant.
Cardiac disease leading indirect cause of death
You have cardiovascular disease before you are pregnant.
What is the recurrence rate of ectopic pregnancy with a history of salpingectomy
15 - 20%
What % of people with GDM go on to have T2DM
30-40% or more
Calculate the interquartile range
Number top 25%
minus
Number bottom 25%
2,3,4,5,6,6,6,7,7,8
7 - 4 = 3
Calculation for the false negative rate
FN/FN+TP
Or if sensitivity is 90% and specificity is 90%
FNR is 10%
Calculate the absolute risk reduction
Placebo 50% risk
New drug 40% risk
ARR absolute risk reduction of 10%
or 0.1
What is the % of BP injury in cases of shoulder dystocia
16%
Rhesus negative incidence in uk
16%
When does the Odds ratio approximate risk ratio?
When the disease studied is rare
What kind of data does a histogram present
Continuous
What is the % risk of recurrent preeclampsia?
20%
