00:01
For this exercise, we consider a random sample of 141 people who received hip replacements.
00:08
And of these 141, eight of the hips developed squeaking.
00:14
So we are asked to calculate a 95 % lower bound confidence interval for the proportion of all hip replacements that develop squeaking.
00:25
Now, when we have a large sample like this, a lower bound for the population proportion is given by this formula.
00:36
It's a critical value z sub alpha, sorry, it's the sample proportion minus the critical value z sub alpha times the standard error, which is the square root of the sample proportion, times one minus the sample proportion over the sample size.
00:59
Now the sample proportion for this sample is calculated as 0 .0567 approximately.
01:11
Also, since we want 95 % confidence, this means that alpha is, 1 minus 0 .95, which is 0 .05...