Observational techniques are the ways in which observations can be made. Observations can be anecdotal. Usually, no matter what technique you use, to report the time and length of the observation. Anecdotal information is nominal and is usually just preliminary in research methods. People use it to define behaviors and develop hypotheses. Once these are defined, the person develops classes of behaviors and might indicate time intervals in which these behaviors can be observed. More can be learned of these methods by exploring observation techniques used in applied behavior analysis. These methods of observation allow a person to use other levels of measure and analysis, such as interval measures or ordinal measures, maybe even random measures, allowing the use of descriptive and inferential statistics.
Descriptive methods refers to actually writing and defining what techniques and their procedures were used to collect the data, who collected the data, and how they were trained to collect the data.