Author information from the last article
E-post: stian.lydersen@ntnu.no
Stian Lydersen er dr.ing. og professor i medisinsk statistikk ved Regionalt kunnskapssenter for barn og unge – psykisk helse og barnevern (RKBU Midt-Norge) ved Institutt for psykisk helse, NTNU.
Articles by Stian Lydersen
26.03.2020:
In a randomised controlled trial there should be no systematic differences in background variables between the groups before treatment. But sometimes it can be sensible to adjust for some pre-defined variables in the statistical analyses. In some studies there are background variables which are...
09.03.2020:
In a randomised controlled trial there should be no systematic differences between the groups before treatment. Still, some researchers choose to significance test for possible differences in background variables. This is superfluous, and can be misleading. An important strength of randomised...
Is the effect small or large?
- Stian Lydersen
17.02.2020:
How do we quantify the results of a study? Is the effect measured on the original scale or a standardised effect size most relevant? Reindal and colleagues (1) studied age for onset of independent walking. For children diagnosed with autism spectrum disorder, the mean age (standard deviation) was 14...
Last observation carried forward
- Stian Lydersen
23.05.2019:
In a longitudinal study, data on one or more time points may be missing for some participants. 'Last observation carried forward' is a simple method for imputing missing values, but it has serious weaknesses. Missing data may arise from participants dropping out of the study, or temporarily failing...
Use of botulinum toxin A in children with cerebral palsy
- Anne Elisabeth Ross Raftemo,
- Arani Mahendran,
- Sandra Julsen Hollung,
- Reidun Birgitta Jahnsen,
- Stian Lydersen,
- Torstein Vik,
- Guro Lillemoen Andersen
24.04.2019:
Cerebral palsy is a collective designation for a group of conditions caused by a brain injury that occurs during pregnancy or in the course of the two first years of life (1). Each year, 2–3 children per 1 000 live births are given this diagnosis (2). Based on the dominant symptoms, cerebral palsy...
Statistical power: Before, but not after!
- Stian Lydersen
28.01.2019:
Some journals, and some reviewers, request a calculation of statistical power based on the observed effect size after a study has been carried out. This is fundamentally flawed. Statistical power is the probability of rejecting the null hypothesis in a future study. After the study has been carried...
Balanced or imbalanced samples?
- Stian Lydersen
17.09.2018:
When comparing two groups, the groups are usually planned to be equally large. But moderate imbalance need not cause a notable reduction in statistical power. And in some settings, imbalance can give increased statistical power. In randomised controlled trials, the groups are usually planned to be...
Stroke - a study of clinical handling and progress
- Jan Hysing*,
- Marjut Sarjomaa*,
- Karina Skog,
- Stian Lydersen
17.05.2007:
During the last 20 years, there has been an ever-increasing development of acute treatment, rehabilitation and secondary stroke prophylaxis. Diagnosis of the condition has improved with routine use of CT caput and establishment of separate stroke units in many places (1, 2). New medicines have been...