Making decisions - L8

What are the uses of Z scores?

• To compare a subgroup sample characteristic with a known population parameter, e.g. does a participant in the study have a different height to that of the whole study

• To compare a sample characteristic with a known population parameter, e.g. do underweight women have a different mean haemoglobin level to that of all women in the study

What is the z score boundary for the 5% critical value?

± 1.96

What is the z score boundary for the 1% critical value?

± 2.58

What is an alpha level?

A significance level

Why is a significance level of 0.1% not used?

Because it would increase the number of times that H_o is accepted when it should be rejected

What is a type 1 (alpha) error?

The null hypothesis is wrongly rejected and the alternative hypothesis is wrongly accepted

What is a type 2 (beta) error?

The alternative hypothesis is wrongly rejected and the null hypothesis is wrongly accepted

What is a z test?

Attempting to reject the null hypothesis by comparing a z score to a critical value

What is a two-tailed test?

A non-directional test where the x% risk of error is allocated to both sides of the distribution

When is the null hypothesis rejected in a two-tailed test?

When the sample statistic is equal to or greater than the critical value at either tail

What is a one-tailed test?

A directional test where the x% risk of error is allocated to only one side of the distribution

When is a one-tailed test used?

In cases where any association can only be in one direction

When is the null hypothesis rejected in a one-tailed test?

When the sample statistic is equal to or greater than the critical value at only one end of the distribution

What are the 5 parametric assumptions?

• Normality - the data is normally distributed

• Independence - data points are independent to each other

• Homogeneity - the variability in the groups being compared is similar

• Randomness - random sample

• Absence of outliers and linearity - no extreme scores and no linear relationship

When is a z test used?

• The population standard deviation is known

• The population standard deviation is unknown and there is a sample size greater than 30

When is a t test used?

When the population standard deviation is unknown, the sample size is less than 30 and the data is normally distributed

When is a sign test used?

When the population standard deviation is unknown, the sample size is less than 30 and the data is skewed

Whet is kurtosis?

A measure of how peaked or flat the distribution is

What is platykurtic?

A flat distribution

What is leptokurtic?

A very peaked distribution

What type of test is a t test?

Parametric

What type of test is the sign test?

Nonparametric