Large data set Flashcards
In the large data set why do some days have gaps
In the LDS, some days have gaps because the data wasnt recorded
(There are some days with no recorded data)
Explain why you have to clean the data before taking a sample
Trace data needs to be converted to numbers before calculations can be carried out
Daily mean pressure units
Hectopascal
Cloud cover units
Oktas
Daily mean visibility units
Decametres
Daily mean windspeed and direction units
Knots
Daily total rainfall units
Millimetres (mm)
How to write probability distribution for cloud cover
Random variable C can only be between 0 and 8 as cloud average is measured on a scale of 0-8 (oktas)
2 marks
Explain how the data will need to be cleaned before Ben can start to calculate statistics such as the mean and standard deviation
- Need to replace tr with a numerical value
- Value of tr is between 0 and 0.05 suggest using e.g 0.025 , 0 or value 0.05
2 marks
State two variables from the LDS for Beijing that are not suitable to be used to be modelled by a normal distribution. Give a reason for each answer
Daily mean wind speed/Beaufort conversion since it is qualitative
Rainfall since it is not symmetric/lots of days with 0 rainfall
Cloud cover summary
This is a discrete variable in the data set. It is measurement of the fraction of the celestial dome covered
by cloud.
It is measured in eighths. The technical unit used in this case is called oktas.
0 oktas indicates a completely clear sky, while 8 oktas indicates complete overcast.
Daily Maximum Relative Humidity summary
Relative humidity is a measure of how close the air is to being saturated with water vapour.
Values for this are recorded as percentages (%). Relative humidities above 95% are associated with mist
and fog. If a reading is not available, it is listed as ‘n/a’.
Daily Mean Wind Direction summary
Two data processes are used to obtain this. The mean direction of the wind is calculated each hour. The
value for the daily mean wind direction is then recorded in the LDS as the most frequently recorded (i.e.
modal) wind direction of these hourly data captures.
The value is given in degrees relative to the true north. The corresponding cardinal direction is also
given.
Daily Mean Windspeed summary
The daily mean windspeed is given in knots. 1 knot is 1.15 mph. If a reading is not available, it is listed as
‘n/a’.
The windspeeds are also categorised according to the Beaufort scale. This is an empirical and discrete
scale.
Daily Maximum Gust summary
The maximum gust speed is the maximum instantaneous speed that occurred over a 24 hour period.
It is calculated as an average over a 24 hour period. If a reading is not available, it is listed as ‘n/a’.
Pressure summary
This is recorded in hectopascals (hPa).
The previous unit for measuring pressure was the millibar (mb).
1 bar is 1000 millibars and 1 millibar = 1 hectopascal.
