Deterministic effects are best described as:

Deterministic effects are defined as biological responses that occur predictably and with a certain threshold depending on the level of dose received. Unlike stochastic effects that have a probabilistic nature and can occur without a discernible dose threshold, deterministic effects become more severe as the dose increases and have a clear relationship between dose and severity of the effect.

For example, effects such as skin burns, radiation sickness, and damage to tissues are directly correlated with dose levels; a higher exposure leads to greater severity in symptoms after surpassing a specified threshold. This clarity in outcomes helps in anticipating the consequences of radiation exposure in clinical settings.

In the context of the other options, unpredictability, randomness, and difficulty in measurement do not align with the nature of deterministic effects, which are well-defined and quantifiable based on established dose-response relationships. Thus, these effects allow for reliable predictions about the biological outcomes following exposure to radiation.