Statistics Flashcards
What are the characteristics of an interval variable?
it has order and equal spacing (intervals) between items
eg. temperature
What is statistics?
the process of representing or analyzing numerical data
What are the characteristics of a ratio variable?
order, equal intervals, and a real zero
eg age
What is the name for a graph with plotted points connected by lines?
a frequency polygon
What category do the mean, median, and mode belong to?
measures of central tendency
What is another term for the range of data?
the spread of the data
How is the standard deviation calculated?
- subtract each value from the mean
- square each of these (to remove negatives)
- add up the sum of the squared values
- divide the sum of squares by number of values (n)
- take the square root
How are the variance and standard deviation related to each other?
the STDEV is the square root of the variance
What is a unimodal distribution?
a distribution with only one peak
What is a z-score?
a representation of how many STDEVs a value is from the mean
In a standard normal distribution, what are the mean and standard deviation?
mean = 0
standard dev = 1
What percentage of a population will fall within 1 standard deviation of the mean in a normal distribution?
34.13% above + 34.13% below = 68.26%
What percentage of a population will fall within 2 standard deviations of the mean in a normal distribution?
95.44%
What is a bimodal distribution?
a distribution with two peaks, with a valley in between
What is the characteristic of a negatively skewed distribution?
the low tail trails off for a long time, with the peak pushed to the right/positive end
What is the characteristic of a positively skewed distribution?
the high tail trails off for a long time, with the peak pushed to the left/low end
What is an example curvilinear correlation?
arousal and performance, which has a inverted U relationship
When can the Spearman r correlation coefficient be used?
when the values are ranked/ordinal values
What are the minimum and maximum values of a Pearson’s r correlation?
-1 and +1
How do the terms statistics and parameters relate to each other?
statistics refer to numbers that describe a sample
parameters refer to numbers that describe populations
statistics are used to estimate parameters
What is a Type I error?
the 1 in 20 error that you found sig results when in fact it was such random sampling variation
What is a Type II error?
not finding sig (for example, sample too small) even though there is a real difference between groups
What can a Chi-square test tell us about two groups?
whether the two groups differ in size or proportions
What are linear regressions used for?
going from correlation coefficients to predictions
eg can now predict dependent variable from score on independent variable
