data test

• • A research question is a question posed by a researcher, which they then seek to answer by conducting an investigation. Every investigation begins with a research question.
• • A hypothesis is a clear statement predicting how changes in the independent variable will affect the value of the dependent value and is based on the information gathered previously
• The research method determines how the researcher will test the hypothesis.
• Sample – the subset or smaller group of participants that are chosen to take part in the research.
• Participant allocation must be done in a systematic and carefully planned manner to ensure that participants’ individual characteristics are evenly distributed among the groups. 
• Experimental group - the group exposed to the experimental conditions
• Control group the group that receives either no treatment or some kind of placebo treatment.
• Convenience sampling is a type of non-probability sampling in which researchers draw the sample from the people who are easily available at the time.
• Random sampling is a sampling procedure in which every member of the population has an equal chance of being selected in the sample.
• Stratified random sampling is a process by which the effects of a certain variable can be eliminated as a possible confound in an experiment.
• The median is less affected by outliers and skewed data than the mean and is usually the preferred measure of central tendency when the distribution is not symmetrical.
• A high standard deviation shows that the data is widely spread (less reliable) and a low standard deviation shows that the data are clustered closely around the mean (more reliable).
• Non-parametric tests are useful for non-representative populations and/or small samples
• Use non-parametric if data is nominal or ordinal. Use parametric if data is interval or ratio.
• The two-sample t-test is a parametric test that assumes that

  data are normally distributed.
• The unpaired t-test, or t-test for independent groups, compares

  two different sets of subjects, whereas the paired t-test, or

  within-subjects t-test, makes comparisons between the same

  set of subjects exposed to two conditions
• The paired t-test minimises participant variables, and is thus

  theoretically more statistically powerful
• Mann-Whitney U test is the non-parametric equivalent of the unpaired t-test and is typically used for ordinal data to test whether two means are equal or not.
• Nominal data is qualitative, no ranking or order
• Ordinal data has a sequence but irregular gaps between levels.
• Interval- steps in the scale are evenly placed but zero does not mean zero.
• Ratio - Steps in the scale are evenly placed and zero means zero
• The Wilcoxon signed-rank-test is the non-parametric equivalent of the paired t-test. It is used as an alternative to the t-test when the population cannot be assumed to be normally distributed. It compares two sets of scores from the same set of participants when the data is not normally distributed.
• The Pearson correlation coefficient is a parametric statistic that represents the strength of the linear relationship between two normally distributed variables. A change in one variable is associated with a proportional change in the other variable
• The Pearson correlation coefficient (designated by the symbol r) is a parametric statistic that represents the strength of the linear relationship between two normally distributed variables. A change in one variable (variable A) is associated with a proportional change in the other variable (variable B).