Psychology Research And Statistics

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Descriptive Statistics

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Numerical and pictorial information about variables.
Mean, mode, median, St.dev and range
Statistics which describe the sample data without drawing inferences about the larger population.

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external validity

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characteristics of a study that refers to the extent to which findings can be generalised to individuals, settings and conditions beyond the scope of the specific experiment

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Co-variance

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A measure of how much 2 variables change together

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Correaltion

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Shows the relationship between two variables. NOT causation!

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Internal Validity

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Changes to dependent variable are due to independent variable. Ensures an unambiguous interpretation for the outcome of the experiment.

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Effect Size

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A measure that indicates the strength of the relationship between the independent variable and the dependent variable

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Meta- Analysis

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Summary of results of more than one experiment on an important research problem

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Type I error

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Rejecting the null hypothesis when the null is true. (Saying something is meaningful when it is not)

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Type II error

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Accepting the null hypothesis when it is not true. (Saying something is not meaningful when it is)

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Statistical inference

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The process of estimates and conclusions carefully based on data from a sample.

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Sample

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A sub-group that is representative of the population

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Population

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The entire group of interest for a statistical conclusion

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Extraneous variables

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potential variables that are not of interest to the researcher.

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Demand Characteristics

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Participants interpret the experiment's purpose and unconsciously change their behaviour

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Within Groups

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Repeated measures: one group tested twice to see if there is a difference between conditions
Use dependent t-test

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When to use dependent t-test

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Data is normally distributed
When there are 2 levels to the independent variable
Within groups design

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Sig > .05

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Probability that there is no difference
Stick with null hypothesis
The assumption of normality/homogenity was not violated

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Sig < .05

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Probability that there is a difference
Enough evidence to reject null hypothesis
The assumption of normality/homogenity was violated

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Confidence interval depends on

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sample size, sample mean and confidence level

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A very small sig value allows...

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the researcher to conclude that there is enough evidence to reject the null

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Anova

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Comparing the means. An expansion of t-test to more than 2 groups

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Test of Homogenity

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statistical test checking the assumption of equal SD in both groups

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Post hoc test

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Looking at data after experiment has concluded
Only use if there is a significant difference

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Causation

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two variables are causally related if changes in the value of one cause the other to change.

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Confidence Interval

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An interval, with limits at either end, with a specified probability of including the parameter being estimated.

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Point Estimate

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Single value that represents the best estimate of the population value

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Interval estimate

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Builds on the point estimate to produce a range of values

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Confirmation bias

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A tendency to favour information that is consistent with pre-existing beliefs

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Operational defintion

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Defining a term for research accuracy

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Alpha

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the probability of Type I error

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Boxplot

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The graphical representation of the dispersion of a sampel

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Categorical data

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Data representing counts or number of observations in each category.

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Chi-Square test

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A statistical test often used for analysing categorical data.

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Critical Value

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The value of a test statistic at or beyond which we will reject H0 .

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Inferential statistics

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That branch of statistics that involves drawing inferences about parameters of the population(s) that have been sampled.

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Interquartile range

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The range of the middle 50% of the observations.

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Kurtosis

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A measure of the peakedness of a distribution.

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Measures of central tendency

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Numerical values referring to the centre of the distribution.

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Mutually exclusive

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Two events are mutually exclusive when the occurrence of one precludes the occurrence of the other.

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Negative relationship

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A relationship in which increases in one variable are associated with decreases in the other.

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Negatively skewed

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A distribution that trails off to the left.

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One-Way Anova

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An analysis of variance where the groups are defined on only one independent variable.

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Outlier

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An extreme point that stands out from the rest of the distribution.

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Parametric tests

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Statistical tests that involve assumptions about, or estimation of, population parameters.

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Positively skewed

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A distribution that trails off to the right.

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Variance

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The sum of the squared deviations from the mean, divided by the degrees of freedom (N- 1).

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Dependent t-test

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compares the means between 2 related groups on the same continuous variables

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Assumptions of a dependent t-test

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1. DV is measured on ratio/interval level
2. IV consists of 2 categorical related groups
3. No significant outliers in the difference between the two related groups
4. Distribution of the differences in the DV between the two groups in approx normally distributed

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One Way Anova Between Groups

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stands for one way analysis of variance
used to determine whether there are any significant differences between the means of 2 or more independent groups

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Assumptions of One Way ANOVA

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1. DV is measured on interval/ratio level
2. IV consists of 2 or more categorical independent groups
3. Independence of observation (no pp in more than one group)
4. No significant outliers
5. DV should be approx normally distributed for each category of the IV (Shapiro Wilk test)
6. Homeogenity of Variance (Levene's)