Presentation of quantitative data + Maths skills Flashcards
What does a bar chart represent?
- Type of graph in which the frequency of each variable is represented by the height of the bars
When should bar charts be used?
- data is divided into categories (discrete data)
How should data on bar charts be plotted?
- categories should occupy the x-axis
- the frequency/amount of each category plotted on the y-axis
- bars should be separated to denote that we are dealing with separate conditions ( categories not continuous)
- always have a title, label columns & axis
What does a histogram represent?
- A type of graph which shows frequency, the area of the bars (not just height) represent frequency
When should histograms be used?
- when data is continuous e.g. scores, age
How should data on histograms be plotted?
- x-axis must start at 0
- x axis is made of equal sized intervals of a single category
- y axis represents the frequency within each interval
- if there is a zero frequency for one of the intervals, interval remains the same with no bar
- always have a title, label columns & axis
What type of data is represented on a scatter graph?
- represents the strength & direction of the relationship between co-variables in a correlational analysis
How should data be plotted on a scatter graph?
- co-variables can occupy either axis
- always have a title, label columns & axis
What does a normal distribution represent?
- A symmetrical spread of frequency data that forms a bell shaped pattern
Characteristics of a normal distribution
- most items are located in the middle area of the curve (very few at extreme ends)
- the mean, mode & median all occupy the same midpoint of the
curve, highest peak (same/similar) - tails of the curve never touch the x-axis (never reach zero)
What is a skewed distribution?
- spread of frequency data that is not symmetrical, data clusters to one end
What is a posiitve skew?
- a type of frequency distribution in which the long tail is on the positive (right) side of the peak & most of the distribution is concentrated on the left
- produced when scores are mostly low
How are the measures of central tendency affected by a positive skew?
- The mode remains at the highest point of the peak
- median next
- mean is dragged towards tail to the right (extreme scores affect the mean)
What is a negative skew?
- a type of frequency distribution in which the long tail is on the negative (left) side of the peak and most of the distribution is concentrated on the right
- produced when scores are mostly high
How are the measures of central tendency affected by a negative skew?
- mode is at the highest peak
- median next
- mean pulled to towards tail left of peak (due to lower scores)
How to work out a percentage of something?
- value over total number x100
How to convert a percentage to a decimal?
- divide by 100
converting a decimal to a fraction
- the number of decimal places equals the number of zeros it is over
e.g.0.81 has 2 d.p.
>8 1/100
formula for standard form
(number between 1 an 10) x 10 ^ (to the power of x)
What is a sign test?
- a statistical test used to analyse the difference in scores related items
- data should be nominal
To use the sign test what should occur
- need to be looking for a difference
- need to have a repeated measures design
- need date that is organised into categories (nominal data)
What is the accepted level of significance in psychology?
0.05 = 5%
= level at which researchers decides that the findings are significant (meaningful) & will reject the null hypothesis and accept the alternative hypothesis
Steps for the sign test to work out calculated value
- work out difference between categories
- if answer is positive record + sign
if answer is negative record - sign - ignore if their is the same result in both categories & adjust total number of N
- add number of pluses and minuses
- take the less frequent sign & call s = calculated value
What information is needed to locate critical value on a table?
- significance level (generally 0.05 or 5% unless said otherwise)
- the number of p’s in investigation (N value or sometimes degrees of freedom df)
- whether the hypothesis is directional (one-tailed) or non-directional (two tail)
For results to be significant what does calculated value need to be?
- calculated value has to be EQUAL to or LOWER than the critical value for the results to be significant
