How to calculate CRRA bounds from Holt and Laury (2002) type lottery? Lottery is between:

Option A: a certain choice of £5

Option B: £10 with probability 0.1 and £1 with probability 0.9

The probability of receiving £10 increases in each subsequent choice.

How do I calculate the CRRA bounds of this, using $U(x) = \frac{x^{(1-r)}}{1-r}$?
Let me rewrite your Option B as follows: £10 with probability $p$ and £1 with probability $1-p$ where $p\in[0,1]$ varies across the items in the list of options. 

Let $\bar p$ be the point where the subject's choice switches. For example, subject chooses Option A for all $p&lt;\bar p$ and Option B for all $p&gt;\bar p$. Then we can use the indifference condition
\begin{equation}
U(5)=\bar pU(10)+(1-\bar p)U(1)
\end{equation}
to infer the risk aversion parameter $r$. 

In experiments where $p$ is discretized, we can take $p_0,p_1$ as the values that are immediately before and after the switching point in choice list. For example, subject chooses Option A for all $p\le p_0$ and Option B for all $p&gt;p_1$. Then the bounds on the risk aversion parameter can be inferred from the following inequalities: 
\begin{equation}
U(5)\ge p_0U(10)+(1-p_0)U(1)
\quad\text{and}\quad 
U(5)\le p_1U(10)+(1-p_1)U(1).
\end{equation}