Dr. kirch is a psychiatrist and finds that 70% of his patients qualify as having symptoms of sleep disorders, according to the results of a questionnaire. dr. kirch reports that 70% of the population must have the same condition as well. however, this study lacks due to his biased sample.

This study lacks generalizability.
Generalizability is an academic term and describes the process of extending research findings and observations from a study on a sample population to a larger and more diverse population. The larger the sample population, the easier will be to generalize the results to the wider population. In this example, Dr Kirch used a sampling technique called convenience sampling, which involves the selection of the most available and proximate subjects. However, there is sampling bias since the sampling population is not representative of the entire population and therefore the study can not speak for the entire population.

This movement is also referred to as  glacial plucking

Ican't see the images : (