1. ARA0103 Aðferðafræði Rannsókna
TFV0103
ARA0103 Aðferðafræði Rannsókna
Fyrirlestur 18 Statistical tests and article quality Tölfræðipróf og greinargæði
decision tree/ákvörðunartré
21/09/2018
Dr Andy Brooks

2. (c) Thomson Learning, Inc.
Central Limit Theorem/Markgildissetningin
Distribution of x: n = 2 30
Population/Þýði 30
non-normal
Distribution of x: n = 10
Distribution of x: n = 30
~normal
21/09/2018
(c) Thomson Learning, Inc.

3. Parametric and non-parametric tests
parametric test/stikapróf
non-parametric test/stikalaust próf
Parametric and non-parametric tests
If the distribution is non-normal and you use small sample sizes...
Then you should not use a t-test or ANOVA.
Ekki geta.
Teikna stöplarit og kíkja á sjálf.
Ef n < 10, greina varlega...
21/09/2018
Dr Andy Brooks

4. Which statistical test?/Hvaða tölfræðipróf?
var kí-kvaðrat próf
Which statistical test?/Hvaða tölfræðipróf?
námkvæmt próf Fisher
krosstöflur
frequency data
Fisher´s Exact Test
gögn af tegund
type of data
normal data
non-normal data
dreifing er ósamhverf
21/09/2018
Dr Andy Brooks

5. Which statistical test. /Hvaða tölfræðipróf
Which statistical test?/Hvaða tölfræðipróf? normal data: 2 variables/2 groups
fylgni
correlation
Pearson´s r
                                                
tilgáta af tegund
dreifni
type of hypothesis
variance
F test
meðaltöl
means
independent samples
independent t-test
paired samples
óparað t-próf
dependent/related/paired t-test
parað t-próf
21/09/2018
Dr Andy Brooks

6. Which statistical test. /Hvaða tölfræðipróf
Which statistical test?/Hvaða tölfræðipróf? non-normal data: 2 variables/2 groups
fylgni
correlation
Spearman´s rho
tilgáta af tegund
type of hypothesis
meðaltöl
means
independent samples
Mann-Whitney test
Viðvörun:
Non-parametric tests have less power.
paired samples
Wilcoxon signed test
21/09/2018
Dr Andy Brooks

7. Which statistical test. / Hvaða tölfræðipróf
Which statistical test?/ Hvaða tölfræðipróf? normal data: more than 2 groups, 1 or more factors 1
ANOVA
fjöldi háðbreyta
number of
dependent variables
> 1
MANOVA
(not available in Excel)
21/09/2018
Dr Andy Brooks

8. Article quality/Greinargæði er tilraunartegund tilgreint?
cross-sectional/þversniðsrannsókn
longitudinal study/langtímarannsókn
Article quality/Greinargæði er tilraunartegund tilgreint?
True experiment ?
PEDro scale
Quasi-experiment ?
Preexperimental ?
Nonexperimental ?
Prospective ?
Retrospective ?
Cross-sectional ?
Data collected at the same point in time.
Longitudinal ?
Data collected at several points in time, maybe over years.
I was forced to read the first two pages to find out what kind of experiment it was. They could have said all this in the abstract.
21/09/2018
Dr Andy Brooks

9. Article quality/Greinargæði Eru núll og hin tilgátur tilgreindar?
Það er ekki auðvelt að skrifa vel núlltilgötu og hin tilgötu.
It is bad to describe the aim of an experiment informally/óformlega.
“We expect the new drug to be better.”
Faster acting?
More long lasting?
Fewer side effects?
Fewer adverse reactions when used with other drugs?
Cheaper to produce?
óviss
21/09/2018
Dr Andy Brooks

10. Article quality/Greinargæði Has the data been checked for normality?
Parametric tests/stikapróf are often applied without first checking that the data is normal.
If the group sample sizes are large (n >30), this is acceptable.
If the group sample sizes are small (n <10), then the results of parametric tests will be wrong (the p value will be wrong) if the data is non-normal.
Sometimes the results of both parametric and non-parametric tests are reported when there are doubts about the data.
Some researchers find this acceptable, especially when group sample sizes are below 30.
Other researchers argue you should make a decision and use the correct test.
21/09/2018
Dr Andy Brooks

11. Article quality/Greinargæði Are the results of statistical tests reported?
Is the statistical test named?
paired t-test, independent t-test (unequal variances), ...
Er tölfræðipróf nefnt?
Is the statistical significance level reached stated?
“reject at the 0,05 level” (p < 0,05)
“reject, as our p was 0,03”
Er p-gildi tilgreint?
21/09/2018
Dr Andy Brooks

12. Article quality/Greinargæði Are descriptive statistics reported and are graphs used ?
For each variable:
mean (meðaltal)
standard deviation (staðalfrávik)
standard error (staðalvilla)
minimum (lágmark)
maximum (hámark)
Are pie-charts or boxplots or line graphs used to explain the statistical results ?
Það hjálpar mikið að teikna gögnin.
An article missing descriptive statistics and graphs can be very difficult to understand.
Afar erfitt að skilja grein án lýsandi tölfræði og gröf.
one or the other
21/09/2018
Dr Andy Brooks