### Video Transcript

The time series graph gives the number of members of a judo club between 2010, the
year it was founded by a judo teacher, and 2018. Describe the trend in the number of members of the judo club between 2010 and
2018.

A time series graph shows how a quantity changes over time. The time, which in this case is the year, is on the horizontal axis. And the quantity, the number of members, is on the vertical axis. Each point then represents the number of members in that particular year.

A trend is the overall pattern shown in the data, ignoring any minor
fluctuations. Looking at the graph, we can see that the number of members in this judo club
initially increased between 2010 and 2014, as new members are joining the club. The graph then levels off, which means that the number of members remains fairly
constant for the rest of the time period, between 2014 and 2018.

Using the graph, give a prediction of the number of members of this judo club in the
year 2020. We’re being asked to make a prediction for what will happen two years into the
future. As the number of members has remained fairly constant for the last four years, we can
assume it will stay around this level in the future. The value on the vertical axis that the graph has leveled off at is approximately
40. So this is our prediction for the number of members of the judo club in 2020.

Is your prediction reliable? Give a reason for your answer. The point here is that we don’t know what will happen in the future. We’ve assumed that the number of members will remain fairly constant. But it could go up or down. We’ve extrapolated the pattern that we’ve seen so far two years into the future. But we’ve no guarantee that this pattern will continue. This means that our prediction is not reliable. And as we’ve discussed, it’s because we don’t know for certain what will happen in
the future.