External validity

External validity

External validity

8.1. External validity I
8.1. A) What is external validity?
8.1. B) How is external validity established in a study?

8.2. External validity II
Randomised, cluster, controlled trial investigated whether a comprehensive warm up
programme prevented injuries in football players. Control treatment was the standard
warm up programme. Football clubs were randomised to the intervention or control
group. At each club, young female players aged 13 to 17 years followed the club’s
allocated programme for one season. The number of overall injuries was statistically
significantly reduced by the comprehensive warm up programme when compared with
standard warm up. However, there was no difference between treatment groups in the
number of injuries to the lower extremities (foot, ankle, lower leg, knee, thigh, groin, and
hip).Would you be able to conclude about the comprehensive warm up programme
(compared with standard warm up) that:
8.2. A) It reduces the number of overall injuries in young male footballers
8.2. B) It reduces the number of overall injuries in female footballers aged over 17 years
8.2. C) It reduces the number of overall injuries in young female footballers if continued
for more than one season. Why or why not?
8.3. External validity III
A randomised controlled trial assessed the efficacy of a psychological intervention in
improving the mother-infant relationship and security of infant attachment postpartum. A
consecutive series of 452 women in their last trimester of pregnancy who were living in
poverty in a crowded South African settlement were identified. All the women were
invited to take part in the study, 100 of whom refused. The remaining women were
randomly assigned to receive the intervention (n=170) or to a control group (n=182) that
received no therapeutic input. An analysis was conducted with data from 18 months
postpartum. A total of 55 women in the intervention group and 52 in the control group
were excluded from the analysis because no information was available—the women
had a miscarriage or stillbirth, moved away, disappeared, or withdrew consent.
Select one option below and explain why it is true or false and how it may impact on
external validity.(Think about table 8.2: A conceptual framework to assess external
validity beyond eligibility criteria)

8.3. A) Before randomisation, the trial participants were representative of the population
8.3. B) At baseline, the two treatment groups were each representative of the population
8.3. C) The treatment groups had similar baseline characteristics following
randomisation
8.3. D) The treatment groups were similar in composition at 18 months postpartum

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