Describing Graphs Using your knowledge to describe the
Describing Graphs Using your knowledge to describe the features of graphs
For each sample make descriptive statements about- Spread - Shape - IQR Describing
�You should ask yourself about how the data is spread out: ◦ What is the range? ◦ What is the IQR? ◦ How big is the IQR compared to the range? ◦ Are the quarters even? �You should be able to describe the situation using correct terminology. Spread
�Generally we compare the data to a normal distribution (pictured below) Shape
�To get an idea of shape you can sketch a rough outline of your distribution. �Is the data grouped in certain locations? �Is the data unimodal (is there one clear peak)? �Is the data skewed? Shape
�Skew- always describe the tail! Shape
BOYS 1 Spread? Shape?
BOYS 2 Shape? Spread?
BOYS 3 Spread? Shape?
�IQR is the middle 50% of the data◦ Its the box in the box and whisker plot! �When we compare two subsets we need to compare the IQR’s to make a decision about differences in the population. �If there is a significant separation we can infer a difference in populations. Inter-Quartile Range
�Shift ◦ Is one IQR shifted further up/down the scale than the other? �Overlap ◦ Is there any overlap of IQR’s? ◦ Quantify the overlap Inter-Quartile Range
�Overall Visible Spread is a VISUAL tool designed to help make decisions: ◦ Estimate the OVS ◦ You should sketch the OVS and cut it into sections depending on the size of the sample. ◦ If sample ≈ 30 then estimate thirds ◦ If sample ≈ 100 then estimate fifths ◦ If sample ≈ 1000 then estimate tenths. �This can then be compared to the distance between the medians (DBM). Overall Visible Spread
�Estimate OVS. the DMB just as you estimate the ◦ Sketch the distance between medians. ◦ Compare the DBM to the OVS visually- this is not a calculation. The calculation should only ever be used in extremely close situations. �Make the call based on: ◦ If sample size ≈ 30 then DBM > 1/3 ◦ If sample size ≈ 100 then DMB > 1/5 ◦ If sample size ≈ 1000 then DBM > 1/10 DBM vs OVS
IQR? ?
IQR?
IQR?
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