booklet 3 Flashcards
What are the 2 features of descriptive statistics?
Measures of central tendency
Measures of dispersion
What 3 things are included in measures of central tendancy?
Mean
Mode
Median
(averages)
What 2 things are included in measures of dispersion?
Range
Standard deviation
What is the median?
When do you use it?
Strength and weakness?
Value in the central position of a data set
+ very easy to calculate
- does not include all of the values in its calculations, not as representative, compared to the mean
What is the mode?
When do you use it?
Strength and weakness?
Most frequent score in data set
+ not distorted by anomalies
- sometimes there is no mode
What is the mean?
When do you use it?
Strength and weakness?
Mathematical average
+ representative
- anomalies can distort the data
What is the range?
When do you use it?
Strength and weakness
Difference between the highest and lowest value of a data set
+ easy to calculate
- anomalies can distort the data
What is standard deviation?
When do you use it?
Strengths and weaknesses
Calculation using all data points that produce a single value. The smaller the SD=less spread out/consistent the data is
+ representative
- difficult to calculate, *don’t need to know how to calculate :)
What is a normal skewed distribution?
Graph values forming a naturally occurring symmetrical bell-shaped distribution curve.
More ppts are in the middle, few on either side
What are the characteristics of normal distributions, in terms of mean, mode and median
Mode- highest point in a histogram is the most frequent score
Median- equal number of scores on either side (symmetrical)
Mean- equal number of outlier scores on either side
What are the characterisations of normal distributions, in terms of standard deviation (SD?)
What is statistical infrequency?
Data is normally distributed
68% of scores in the data set fall within one SD
95% of scores are within 2 SDs of the mean
How far someones score is from the mean score, way of defining abnormal behaviour e.g. intellectial disability is an IQ 2 SD below the mean (70)
What is a skewed distribution?
What is the difference between a negative and positive skew?
Distribution of scores is asymmetric, most of the scores are on one side
Positive- more scores at the lower end of the graph, outliers at the higher end
Negative- more scores on the higher end of the graph, outliers at the lower end
What are the characteristics of skewed distributions, in terms of mean, mode and median
Mode- mode is more frequent>remains at the highest point
Median- 50% of the graph is either side (between mode and mean)
Mean- shifted towards the outlier scores in the skew
What are levels of measurement?
Nominal, ordinal, and interval levels of measurement
Each is more presciese and provides more information than the previous level
What is nominal data? E.g?
Categorical data, no order!
E.g. country of birth, career choice, music taste
What is ordinal data? E.g?
Categorical data, that has an order
E.g. position in a competition (1st,2nd,3rd), choices on a likert scale, height amongst a group of people
What is interval data? E.g?
What is ratio data? E.g?
Preciece data due to have the same distance (intervals) that is continious
E.g. Weight in grams, temp in Celsius, time in seconds
Interval data with an absolute zero point E.g. crime rate (you can commit 0 crimes)
Example of levels of measurement in a STEM:
There’s an Olympic sprint race image of the finish line, give examples of all levels of measurement from the image
Nominal- nationalities of the runners
Ordinal- order in which runners finish the race
Interval- record the time each runner finished the race
How can you convert interval to ordinal data?
Get ppt interval scores e.g. reaction times, on a standardised test
Each ppt is assigned a rank score to turn the interval measure into an ordinal meausre
This is done by listing each ppt from the highest scoring to the lowest scoring
Ppts with the same scores=share the same rank position
How can you convert ordinal to nominal data?
Separate categories are created e.g. fast and slow reaction times, introvert and extrovert
Highest ranked half of ppts are assigned to one category, and the other half to the other category
What is a statistical test?
Mathmatical tools researchers use to determine if the results are significant
What is a type 1 error? E.g?
‘False positive’
When the null hypothesis is rejected when it shouldn’t have been
E.g. when a test shows a patient to have a disease, they don’t have
What is a type 2 error? E.g?
‘False negative’
When the null hypothesis is accepted and it shouldn’t have been
E.g. blood test failing to detect the disease it was designed to detect in patient who really has the disease
