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

(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.

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

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

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

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

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

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

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

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

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

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