Voortgezette Statistiek en Onderzoeksmethoden (GZW3024)
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Maastricht University (UM)
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Voortgezette Statistiek en Onderzoeksmethoden (GZW3024)
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Seminar 1
HOMEWORK ASSIGNMENTS
Researchers can quantify the occurrence of disease by making use of measures of disease
frequency (MODF), such as
- Prevalence (and variants of this MODF: point, period, and lifetime prevalence)
- Incidence (and variants of this MODF: cumulative incidence and incidence density)
- Mortality
- Case fatality rate (CFR)
1a. Define all these MODF. How should one calculate these measures?
Prevalentie: heeft betrekking op aantal personen dat op bepaald moment ziek is
- Puntprevalentie = deel van populatie dat betreffende ziekte heeft op bepaald moment
Ndisease at Tx / Ntotal at Tx
- Periodeprevalentie = deel van populatie dat betreffende ziekte heeft gehad in bepaalde
periode = totaal aantal zieken in bepaalde periode / gemiddelde van totale populatie aan het
begin en einde van periode
Ndisease in period P/Ntotal in period P
- Lifetimeprevalentie = of een bepaalde toestand bij een individu tot op dat moment ooit
aanwezig was
Never had the disease/Ntotal
Incidentie: heeft betrekking op het aantal personen dat ziek wordt in een bepaalde periode
- Cumulatieve incidentie (CI) = totaal aantal nieuwe zieken in bepaalde periode / totaal aantal
personen in populatie aan begin van deze periode
Nnew cases in period P/Nat risk at T0
- Incidentiedichtheid (ID) = totaal aantal nieuwe zieken in bepaalde periode / totaal aantal
geobserveerde persoonsjaren at risk gedurende deze periode
Nnew cases in period P/total persontime-at-risk within period P
Mortality rate = totaal aantal sterftegevallen in bepaalde periode / totaal aantal personen in
populatie waaruit deze sterfgevallen afkomstig zijn aan het begin van de periode
Case fatality rate (CFR) /letaliteitspercentage = totaal aantal sterfgevallen door bepaalde ziekte /
totaal aantal incidente patiënten met deze ziekte
Ndeaths due to disease D/Total Npatients with disease D
1b. In which of the following designs can these MODF be calculated? (yes/no)
Prevalence Incidence Mortalit CF
Point Period Lifetime Cl ID y R
- - -
Case series No No No No No No Yes
Ecological study Yes Yes Yes Ye Ye Yes Yes
s s
1
, Cross-sectional Yes Yes Yes No No No No
study
Case-control study No No No No No No No
Prospective cohort Yes Yes Yes Ye Ye Yes Yes
s s
Retrospective cohort Yes Yes Yes Ye Ye Yes Yes
s s
RCT Yes Yes Yes Ye Ye Yes Yes
s s
The following table represents the results from a follow-up study over a period of 12 months. In
this study the participants are continuously monitored for disease D during their follow-up. It is
assumed that all participants are at-risk as long as they are present in the study population
(indicated in yellow), except when they have the disease (indicated in blue).
White:
person # is
not present in
study
population
Yellow:
person # is
present in
study
population
Blue: person
# has disease
D
2
, 2a. What
type of population -‘open’ (or dynamic) or ‘closed’ (or cohort)- is under study? (Justify
your answer.)
Dynamische populatie. De participatie is van variabele duur en de participanten beginnen niet
allemaal tegelijk aan het onderzoek (at-risk, geel).
2b. What are the sex-specific point prevalences of disease D on the second day of the 6th
month? (Males are ID-numbers A1-A24, females are ID-numbers B1-B26)
Puntprevalentie mannen: 2/17 x 100 = 11,8%
Puntprevalentie vrouwen: 2/24 x 100 = 8,3%
2c. Calculate the point prevalence of disease D for the total population on the second day of
the 6th month.
Puntprevalentie totale populatie: 4/41 x 100 = 9,8%
2d. Suppose that people could not be cured from disease D. What would then have been the
point prevalence of disease D on the second day of the 6th month?
Puntprevalentie: 7/41 x 100 = 17,1%
2e. What are now the sex-specific point prevalences of disease D on the second day of the
6th month?
Puntprevalentie mannen: 4/17 x 100 = 23,5%
Puntprevalentie vrouwen: 3/24 x 100 = 12,5%
2f. Calculate the incidence of disease D in the total population.
Het is een dynamische populatie dus incidentiedichtheid moet berekend worden.
3
, ID = totaal aantal nieuwe zieken in bepaalde periode / totaal aantal geobserveerde persoonsjaren
at risk gedurende deze periode
Persoonsjaren: 178+187 maanden = 365 maanden
ID = 15/365 = 0,0410
2g. Are males or females more likely to develop disease D? (Males are ID-numbers A1-A24,
females are ID-numbers B1-B26)
Mannen: 8/178 = 0,0449
Vrouwen: 7/187 = 0,0374
Bij mannen is het hoger dus mannen zijn waarschijnlijker om de ziekte te ontwikkelen
2h. Suppose that due to improvements in the treatment of disease D, the disease duration is
reduced to 50%. What happens to incidences calculated in 2e and 2f
De incidentiedichtheid daalt. Dit komt omdat het aantal geobserveerde persoonsjaren at risk stijgt
en omdat de totaal aantal nieuwe zieken gelijk blijft, daalt de incidentiedichtheid.
For this assignment you can use the data from Statistics Netherlands (CBS – Centraal Bureau
voor de Statistiek): https://opendata.cbs.nl/statline/#/CBS/nl/ . Use the search option, for instance
search (on the Dutch version of the page) for "verkeersongeval".
The Minister of Transport and Water Management of the Netherlands is concerned about the
increased use of mobile phones during traffic participation. Last year it was reported that an
alarming 26,300 traffic tickets were issued because of mobile phone-use. In order to find out
whether there has been an increase in fatal traffic accidents since the widespread use of mobile
phones (the beginning of the 21st century) she asks the Department to report the following
figures:
3a. How many fatal traffic accidents occurred in 2018 in the Netherlands?
678 traffic accidents
3b. How many fatal traffic accidents occurred in 2018 in the Netherlands in the age
categories 0>20; 20->30; 30->40; 40->50; 50->60; 60->70; 70->80; 80+ years of age? Which
category has the highest number of fatal traffic accidents? What is your explanation why
this category has the highest number?
0->20 55
20->30 87
30->40 60
40->50 59
50->60 67
60->70 74
70->80 129
80+ years 143
80+ Jaren heeft de hoogste aantal fatale verkeersincidenten (decreased reaction-time,
balance, impaired vision etc.)
4
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