Research Methods B.1 Flashcards
When planning a histogram, what must we consider?
how many bins to use - increasing bins will give higher resolution, but too many can make the histogram too noisy
What is P-hacking, Publication bias, data dredging and HARKing?
- P-hacking: manipulating analysis to get desired p-value
- Publication bias - outcome of the experiment influences decision to punish or not
- Data dredging - testing many hypotheses and only reporting the significant ones
- HARKing - hypothesising after results are known
What level of data is there no relationship between different possibilities in the scale?
Nominal level
What level of data is there a natural order between possibilities in the scale, but no interpretable magnitude of differences between values of the scale?
Ordinal level
What level of data are the possibilities ordered and have interpretable magnitudes, but zero doesn’t have a special meaning?
Interval level
What is the difference between discrete and continuous data?
Discrete data has clear spaces between values and is countable, continuous data falls in a constant sequence and is measurable
What is a test statistic?
a value that quantifies how close the data is to the null hypothesis
What is a P-value?
a value that shows the probability that we would have observed this same data if the null hypothesis was true
What is the standard error of the mean and how can it be calculated?
- the value that demonstrates the standard deviation of sampling distributions
- calculated by dividing the standard deviation of the data by the square root of the number of samples
if SEM is too difficult to interpret, what is a better, more interpretable metric for the precision of our estimate of the mean?
confidence intervals: for example if we have 95% confidence intervals that mean we have a range of values which have a 95% chance of containing the population mean
In a normal distribution, what percentage of participants lie within one, two and three standard deviations?
- 68.2% lie within one deviation
- 95.4% lie within two deviations
- 99.6% lie within three deviations
What test can be used to test if the data is normally distributed?
Shapiro-Wilk test
What do shapiro wilk W and shapiro wilk P tell us?
-Shapiro-Wilk W is a metric indicating how normal the data is, higher values = more normal data (if the value is greater than 0.05, its normally distributed)
- Shapiro-Wilk P is a probability indicating how significance any difference from normality is
What is ecological validity
the extent to which the variables and conclusions of a study sufficiently reflect the real world context of its population
What does a one-sampled hypothesis discuss?
if the mean of a particular data set is different to a specified value found ahead of time
What are the two reasons that we use a null hypothesis?
- The null should be what we’re willing to assume until the alternate hypothesis is substantially proven (like innocent until proven guilty)
- Its simpler: there are many ways that one thing can affect another, but only one way that there can be no effect
As the difference between the observed data mean and the comparison value gets bigger, what happens to the t-value?
it gets bigger
When reporting t-tests, what are all the values we need to include? (6 points)
Mean, SD, comparison level, t-value (with degrees of freedom in brackets) and p-value
What is the difference between within and between subject designs?
Between subjects: two independent groups: participants change BETWEEN conditions
Within subjects: each participants completes both conditions and contributes two data points
How do we calculate an INDEPENDENT samples t-test?
calculate the difference between the two means of the two groups of data, all divided by the pooled standard error of that difference (this is a single number that represents the variability of both groups, but it does assume that we have HoV because it assumes both groups have the same SD
What do different t-values indicate?
- Large NEGATIVE t-value means mean of group one is less than group 2
- Large POSITIVE t-value means mean of group 2 is less than group 1
- near ZERO t-value means the means are close the the same
What does a significant value from a levene’s test indicate, and what value would mean it was significant?
- p values GREATER than 0.05 suggests there is no significant difference between variances, meaning we DO have homogeneity of variance
If our data fails the levene’s test and we don’t have homogeneity of variance, what alternative to a original t-test do we use?
Welch’s t-test, which uses an unpooled standard error of the difference
How and when do we used a paired sample t-test instead of an independent sample t-test?
- when we use dependent groups
- we calculate the difference between the pair of samples from the same participant in each condition to get a mean of paired differences, then divide that by the standard error of the mean paired difference
What does shapiro-wilk test test for, and if our data fails the test what do we calculate instead?
- tests for normal distribution
- if our data is not normally distributed, (value less than 0,05) we consider are non-parametric alternative such as wilcoxon (one sample test) or mann-whitney U (two sample test)
Why can’t we conduct a t-test on ordinal level data?
Because even though we could use the mean, t-tests also require the SD, which is hard to calculate with ordinal data because we don’t know the exact ‘distance’ between values on the scale
What type of t-test do we use when comparing one sample to a reference
one sample t-test
What is an effect size?
it is a quantitative measure of the difference or relationship between two groups or variables
Why do we use degrees of freedom instead of number of observations?
because we have to account for number of values we’re estimating from the data
- One sample t-test DF = N-1
- Independent sample t-test DF: N1 + N2 - 2
- Paired sample t-test DF = N-1
How do we report p-values?
Specify the degrees of freedom of the test, report exact p values to two or three decimals (but report p values less than 0.01 as < 0.01), specify the significance threshold used