Quantitative - data expressed in numbers or values (e.g. number of pupils with brown hair in a sample = 8 out of 10)
Qualitative - data expressed on a quality scale or observed
Sample - a known proportion of a population that is to be studied
Normal Distribution
Special type of frequency distribution; plotted graph is symmetrical called ‘a bell shaped curve’ and the mean (average), mode (most common) and median (middle) values are the same
True normal distribution is symmetrical: 50% of the values are above the mean and 50% are below and 95% of the values are within 2 standard deviations of the mean
Low SD = data has a narrow range and grouped around the mean (greater reliability), produces a narrow curve and High SD = data has a larger range and is less well grouped (lower reliability), produces a wide curved and SD is large
Spread of measurements about the mean in a normal distribution reduces effect of anomalies and indicates if difference between results is significant; it is the distance from the mean to the point of inflexion on the curve
68% of all measurements lie within 1 standard deviation of the mean, 95% of all measurements lie within 1.96 standard deviations of the mean
Standard deviation formula
Range
Largest value - smallest value
To measure spread, however severely affected by outliers which may skew calculation
If the investigtions involved finding the number of individuals in specific categories - use chi-squared test
If the investigation involved takingmeasurements and looking for associations between different measurements from the same sample - use spearman correlation
If the investigation involved takingmeasurements and looking for associations between measurements from diffferent samples - use two sample t-test (standard error and 95% confidence limits)
