Recap…

We need to take spread into account when we give an interval for the population parameter

So far…

Population

Sample

Sample statistics

Population

parameterWhat we’re trying

to estimate

Remember our kiwis…

So far…

Population

Sample

Sample statistics

What is the median

weights of kiwis?

What we’re trying to estimate

Take your sample of kiwis•Dot plot•Box plot•Sample statistics…

So far…

Population

Sample

Sample statistics

Population

parameterWhat we’re trying

to estimate

Median weight of kiwis is somewhere between ___ and ___

Samples of size ___ were reliable enough

The median weight of kiwis was somewhere between ___ and ___(90% ish of our sample medians)

Distribution of sample medians…

2.2 2.4 2.6 2.8 3.0 3.2median

Measures from Sample of Kiw ipop Dot Plot

We don’t get to take multiple samples so this process WON’T work We need to find an informal confidence interval for the population median based ON A SINGLE SAMPLE

However in real life …

To take into account both•Sample size and•spread

Our informal interval needs…

For your sample of kiwis:•Dot plot•Box plot•Median

More kiwis…

Add your SAMPLE MEDIANS TO THE SHEET

Then

Add your IQR (box) TO THE SHEET

Student worksheet

Complete Q3 – Q5 on the worksheet

Student worksheet

Q3: I notice that the width of the IQR for sample medians when the sample size is 30 is approximately of the width of the population IQR

WIDTH 0.507 kg-ish(67 mm)

WIDTH 0.095 kg-ish(11 mm)

1/5

Q4: I notice that the width of the IQR for sample medians when the sample size is 400 is approximately __________ of the width of the population IQR

WIDTH 0.025 kg-ish(3.5 mm)

WIDTH 0.507 kg-ish(67 mm)

1/20

Q5: Relationship between the width of the IQR for sample medians of sample size n and the population IR and the sample size… IQR for sample medians (sample size = n) is

approximately of the population IQR

When n = 400 the IQR of the sample medians is approximately ________________ of population IQR

When n = 30 the IQR of the sample medians is approximately ________________ of population IQR

n1