  We study the correlation between the non-thermal velocity dispersion
($\sigma_{\rm nth}$) and the length-scale (L) in the neutral interstellar
medium (ISM) using a large number of Hi gas components taken from various
published Hi surveys and previous Hi studies. We notice that above the
length-scale ($L$) of 0.40 pc, there is a power-law relationship between
$\sigma_{\rm nth}$ and $L$. However, below 0.40 pc, there is a break in the
power-law, where $\sigma_{\rm nth}$ is not significantly correlated with $L$.
It has been observed from the Markov chain Monte Carlo (MCMC) method that for
the dataset of $L > 0.40$ pc, the most probable values of intensity ($A$) and
power-law index ($p$) are 1.14 and 0.55 respectively. Result of $p$ suggests
that the power-law is steeper than the standard Kolmogorov law of turbulence.
This is due to the dominance of clouds in the cold neutral medium. This is even
more clear when we separate the clouds into two categories: one for $L$ is >
0.40 pc and the kinetic temperature ($T_k$ ) is < 250 K, which are in the cold
neutral medium (CNM) and for other one where L is > 0.40 pc and T k is between
250 K and 5000 K, which are in the thermally unstable phase (UNM). Most
probable values of $A$ and $p$ are 1.14 and 0.67 respectively in the CNM phase
and 1.01 and 0.52 respectively in the UNM phase. A greater number of data
points is effective for the UNM phase in constructing a more accurate estimate
of $A$ and $p$, since most of the clouds in the UNM phase lie below 500 K.
However, from the value of $p$ in the CNM phase, it appears that there is a
significant difference from the Kolmogorov scaling, which can be attributed to
a shock-dominated medium.
