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Time Series Mark Scheme
Q1.
Qi. Time Series Mark Scheme (a) | Bl 2014 [e) (b) | B1 2008 and 2009 qd) (c) | Bl for upwards B1 for correct statement qd) interpreting the trend (d) | M1 for 81 —8 or 61-13 M1 implied by 73 or 48 (3) Al 73 and 48 ae ; ; Al for correct interpretation B1 for e.g. the difference in percentage of market of data share is greater in 2009 than in 2011 B1 for correct comparison Q2. Question | Answer _Additional guidance Mark (a) Bl eg sales increase (as time goes on) B1 for a description of trend. Accept qd) rising/upward trend (Condone ‘positive’ but ‘positive correlation’ is BO) ()@ | Bi eg sales are higher in each quarter 3. | B1 for correctly identifying a seasonal qd) OR variation lower in each quarter 1 (ii) | B1 eg it is warmer / it is summer / there | B1 for a sensible corresponding suggestion qd) is more demand for drinks, OR itis | why sales are higher in quarter 3 OR why colder / it is winter / there is less lower in quarter 1 demand for drinks (©@ | M1 (180 +260 + 300 + 240) +4 M1 for selecting the last 4 values from the (2) graph (at least 2 correct) and division by 4 al (=2) = 245 Al cao 4 (ii) | B1 ft Their ‘245° plotted midway between | B1ft for correct horizontal positioning of qd) Q2 & Q3. 2017 their moving average Q3. Al 199 Bl fore.g. B1 for an explanation of a (2) (a) « Apilot study is a small scale version of the | pilot study overall study used to evaluate and improve the design of the overall study Bl fore.g. B1 for any sensible reason « makes sure questionnaire gets relevant for doing a pilot study answers Do not allow: « makes sure questions are understood Checks spelling/proofread « to check response rate/likely responses Checks for bias/leading « identifies ambiguity questions * improvements can be made to questionnaire | Checks not offensive «checks how long it will take Bl for e.g. B1 for a correct statement @ (b) e Easy and quick to answer assessing the appropriateness « Response choice can clarify the question of closed questions meaning « Improves consistency of responses « Easy to compare with other respondents or questionnaires « Easier, quick, and less costly to analyse B1 for e.g. the spreadsheet does not add up non- B1 for a correct statement (63) (c) numeric data/gives the wrong total assessing the reliability of the conclusion 17.2417.24+18.6+26.6 (2) ML (d) 4 Q5. Question | Answer Additional guidance Mark number (a) | B1 ‘(Appropriate) since the data is quarterly/follows | B1 for any correct supporting reason| (1) a pattern every 4 quarters’ stating or implying ‘quarters’ or “seasons” (b) | B1 Point plotted at (middle of Q1 and Q2 2017. (1) 1525) (c) | Bl Trend line drawn from (Q3 2015, [1650 to 1750]) (1) to (Q4 2016, [1500 to 1600]) (d)@| B1 e.g. ‘on average the 4th quarter has 140(thousand)| B1 for a correct interpretation in qd) fewer visitors(o.e.) compared to the trend’ context (4)(ii)] M1 ‘1450°(000) - 140(000) Q) M1 for subtracting 140 from the value Al 1225(000) to 1375(000) read off their trend line at (Q4 2017) Al for an answer in the range 1225 to 1375 inclusive Note: 1690 — 140 is MOAO (e) | B1 for each assumption: B1 for each assumption required to use | (2) + ‘overall trend continues” the method + ‘seasonal trend continues” If BO scored, allow ‘trend continues’ or ‘continues to decrease’ to score B1 Q6. Question | Answer Additional Mark number guidance (a)(i) 11.5418 +22.3+13.4 (3) ML ———. Al 16.3 (a)G@i) | B1ft Point plotted at height °16.3° between Q2 and Q3 2015 (b) B1 Quarter 3 (2015) (1) (c) B1 Upwards BI for a correct (2) B1 The number of visits abroad is increasing as time goes by. | description of the trend Bl fora contextualised interpretation (d) B1 e.g. Seasonal variation is highest in Q3/lowest in Q1 BI for a correct (2) Bl e.g. More visits abroad in Q3/Fewer visits abroad in Q1 comparison of one of the quarters with the others Bl fora contextualised interpretation Q7. four quarters the appropriateness of using 4-point moving averages Question | Answer Additional guidance Mark number (a) B1 for a correct statement identifying any B2 for a correct statement (2) seasonality. e.g. the greatest/least values are identifying and interpreting an in quarter 3/ quarter 1 example of seasonality B1 for a correct interpretation in context for (B1 for one of these features) the identified seasonality, e.g. more/less overseas visitors in summer/winter (b) M1 Correct horizontal plotting. first between | M1 for recognising correct (3) Q2/Q3 of 2012 horizontal position for plotting Al All points correct moving averages (at least five correct) Al for accurately plotting all BI Straight trend line through moving moving averages averages within tolerance (Allow within one small square tolerance) BI Their line should extend horizontally at least from 2012 Q3 to 2013 Q4 and be vertically within one square of 7.8 at 2012 Q3 and one square of 8.4 at 2013 Q4 (c) B1 Upward/nising trend Accept equivalent wording (e5) demonstrating statistical reasoning (d) Bl ft trend line value 8.9 (0.1) B1ft for value which follows from | (3) Mifor 8.9— GSS S25 Feed) HEA 89) their line at 2015 QI Al for 7.35 MI for complete method to find seasonal variation for their trend line Al for answer in range [7.2-7.5] (e) BI for e.g. the pattern in the data repeats after | B1 for a correct statement assessing | (1) Qs. Question | Answer Additional Mark ai) 23430 + 22880 + 27430 + 25710 M1 for summing the correct four quarters and Q) ma dividing by 4 Al 24862.5 Al for 24900, 24860, 24863 or 24862.5 (ii) | B1 ft for correctly plotting their point at qd) height ‘24862.5° between Q2 and Q3 2016 (b) | B1 for reference to the truncated vertical B1 for a correct comment assessing why the @ axis OR reference to the graph only graph is misleading showing houses sold over £40 000 (c) B1 for quarter 3 (05) (d) | B1 Upwards oe B1 for a correct description of the trend. Q) Accept positive but positive correlation is BO B1 The number of houses sold is increasing | B1 for a contextualised interpretation as time goes by ) B1 For a complete interpretation of the B1 for a complete contextualised interpretation | (1) gradient of the trend line in context eg of the gradient of the trend line © The number of houses sold is increasing at an average rate of 325 per quarter [ea B1 for correctly identifying a problem with | B1 for a correct comment on the problems of qd) extrapolation eg extrapolation e the trend may not continue Q10. Question Scheme Marks (a) (b) (a *@i) (d) Quarterly figures were plotted OR four quarters/seasons in the year Spending is higher/highest/goes up in quarter 3 (each year) and lower/lowest/goes down in quarter 1 (each year) (eg. 2100=15) E|e = 140 (per quarter), or 560 (per year) (Answer in range 120~160 or 480~640) Spending/£ . increases , by “140° million per quarter (or by ‘560° million per year) Trend line value = 6800 (million) 1400+1700+1500 3 6800- = 5267 (£ million) (accept 5100~5500) Bl @) Bl Bl M1 Al Blft Q) Blcao M1 Al G) [9] Notes (a) (b) ©@ ()Gi) (@) Any reference to 4 values per year or to quarterly figures. For each comment, reference to ‘each year’ is not required but reference to one year (eg 2013 Q3) scores BO. (Condone ‘summer’ for quarter 3, ‘winter’ for quarter 1, 0.e) IN PARTS (c) AND (d) ALLOW +200 FOR GRAPH VALUES USED M1 Gradient attempted, correct way up. May be from triangle on graph. For x may use quarters or years. Al Allow answer in either range, inclusive, for M1A1. Allow equivalent ranges in millions but units not needed for this mark. Note: If correct gradient is in an equation as final answer. then M1A0 Qwc Blft for Increase and figures in millions, £/spending, and time. Follow though their figures. Ignore statements about correlation. Blcao 6800 must be stated or seen used. (May be seen labelled on graph) M1 for subtracting an attempt at mean seasonal variation (using three Q1 values within tolerance) from their “6800° Al Allow answer in range 5100~5500 inclusive. NB: Answer without working scores MOAO Q12. from graph: 16,—-8,7 M1 (mean seasonal variation = ) ‘ae'H-8' 47 —{ 7&4) Mldep (estimate = ) 208 + ‘5° to 209+ ‘5’ Al =213 Alft (Difference is) 9.9 (thousand) condone + values here) 1st M1 for attempt at mean of 3 seasonal variations. 2nd Mldep for complete method with their 5 + trend line value (read at 2018 Q2) May be implied by their mean seasonal variation + 208 or +209 evaluated 1st Al for answer in range 212 - 214 (or 212000 - 214000) 2nd Al ft for “correct” numerical comparison of their estimate with true value. Accept e.g. estimate is about 10000 too high Question Answer Additional guidance Mark | number (a) Bl Upward (trend). or number |B1 for correct description of trend. Accept increasing or | (1) of visitors is increasing ‘positive’ (but not positive correlation). over time. Accept correct interpretation of trend. (b) B1 (Quarter) 4 (each year) _| Note ‘2015 Quarter 4” scores BO @ (c) B1 Number of visitors increases] B1 for correct interpretation. Must have ‘per quarter’ a) by 1400 per quarter (on o.e. and 1400 average) Allow 1.4 thousand for 1400 (d) B1 e.g. Prediction may not be |B1 for a comment recognising that extrapolation is used @ correct as it relies on or that the trend may not continue. extrapolation (Accept as reason that seasonal variation for Q2 is not consistent) (e) B1 Q2 seasonal variations B1 for attempting 3 seasonal variations for Q2 (each +2. ©) Q13. Question Answer Additional guidance Mark number (a) Bl 4 qd) (b) BIB1 B1 for each correct (2) e Lowest in the Quarter 1 (each year) description of the seasonal e Highest in Quarter 2 (each year) trend ¢ Downward from Q2 to Q4 (each year) ; © Quarters 2 & 3 are above the overall For third bullet point accept trend line (each year) / quarters 1 & 4 are | ‘downward from Q@ toQl below the overall trend line (each year) | Do not accept descriptions of overall trend e.g. ‘there is an upwards trend” © Bl 4 Q) B1 since the data is quarterly/repeats every 4 quarters (d) B1 Not reliable due to extrapolation B1 for not reliable and (lL) cofrect supporting reason 
